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  • 151.
    Ferrari, Arnaud
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Högenergifysik.
    Ziemann, Volker
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Högenergifysik.
    Appleby, Robert B.
    Salt, Michael D.
    Conceptual design of a beam line for post-collision extraction and diagnostics at the multi-TeV Compact Linear Collider2009Inngår i: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402, Vol. 12, nr 2, s. 021001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strong beam-beam effects at the interaction point of a high-energy e(+)e(-) linear collider such as the Compact Linear Collider (CLIC) lead to an emittance growth for the outgoing beams, as well as to the production of beamstrahlung photons and e(+)e(-) coherent pairs. In this paper, we present a conceptual design of a 150 m long post-collision extraction line for the CLIC machine at 3 TeV, which separates the various components of the outgoing beam using a vertical magnetic chicane, before transporting them to their respective dump. In addition, detailed studies are performed in order to compute the power losses along the CLIC post-collision line. For the vacuum window at the exit of the post-collision line, we propose a thick (1.5 cm) layer of carbon-carbon composite, with a thin (0.2 mm) aluminum leak-tight foil. The stress levels in this exit window are estimated. Finally, we discuss the use of diagnostics along the post-collision line for monitoring and improving the quality of the e(+)e(-) collisions and, in turn, the luminosity of the CLIC machine.

  • 152.
    Flechl, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Looking for the Charged Higgs Boson: Simulation Studies for the ATLAS Experiment2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The discovery of a charged Higgs boson (H+) would be an unambiguous sign of physics beyond the Standard Model. This thesis describes preparations for the H+ search with the ATLAS experiment at the Large Hadron Collider at CERN. The H+ discovery potential is evaluated, and tools for H+ searches are developed and refined.

    The H+→τν decay mode has been known as the most promising H+ discovery channel. Within this thesis, first studies of this channel with realistic detector simulation, trigger simulation and consideration of all dominant systematic uncertainties have been performed. Although, as shown by these studies, the discovery sensitivity is significantly degraded compared to studies using a parametrized detector simulation, this channel remains the most powerful ATLAS H+ discovery mode. Future searches will rely on multivariate analysis techniques like the Iterative Discriminant Analysis (IDA) method. First studies indicate that a significant sensitivity increase can be achieved compared to studies based on sequential cuts. The largest uncertainty in H+ searches is the expected $t\bar{t}$ background contribution. It is shown that numbers obtained from simulated events could be off by a factor of two, decreasing the discovery sensitivity dramatically. In this thesis, the Embedding Method for data-driven background estimation is presented. By replacing the muon signature in $t\bar{t}$ events with a simulated τ, events which allow an estimation of the background contribution at the 10% level are obtained.

    The ATLAS τ identification focuses on comparably clean environments like Z and W decays. To optimize the performance in high-multiplicity events like H+→τν, tau leptons are studied in $t\bar{t}$ and pile-up events. Variables which do not show discrimination power in high-multiplicity events are identified, and in some cases similar, more powerful variables are found. This allows to recover some of the performance loss and to increase the robustness of the τ identification.

    For the analysis of large amounts of data produced by the ATLAS detector, seamless interoperability of the various Grid flavors is required. This thesis introduces translators to overcome differences in the information system between a number of Grid projects,and highlights important areas for future standardization.

    Delarbeid
    1. ATLAS discovery potential for the Charged Higgs Boson in H+  decays
    Åpne denne publikasjonen i ny fane eller vindu >>ATLAS discovery potential for the Charged Higgs Boson in H+  decays
    2007 (engelsk)Inngår i: CDSArtikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The \textsc{Atlas} discovery potential for the hadronic decay of a heavy charged Higgs boson, H , is presented. A new matched production algorithm for the processes ggtbH and gbtH is used allowing to span the investigated mass range from mHmt up to mHmt with a consistent treatment of the transition region. For the considered charged Higgs boson masses from 165 to 600 GeV, H is the most relevant decay channel together with Htb . Whereas the latter suffers from large irreducible backgrounds, the decay channel offers a decisively cleaner signature. This is the first \textsc{Atlas} Full Simulation study of the H channel. For the background, \textsc{Atlas} Fast Simulation is used for the investigation of a greater variety of channels than in previous studies, emphasizing the need for new selection cuts with additional discriminating power between signal and background. Such cuts are introduced and it is shown that current limits from direct charged Higgs boson searches can be substantially extended already with a few years of LHC data.

    Emneord
    ATLAS Charged Higgs
    Identifikatorer
    urn:nbn:se:uu:diva-110659 (URN)
    Tilgjengelig fra: 2009-11-21 Laget: 2009-11-21 Sist oppdatert: 2011-03-04bibliografisk kontrollert
    2. Charged Higgs Boson Searches
    Åpne denne publikasjonen i ny fane eller vindu >>Charged Higgs Boson Searches
    2008 (engelsk)Inngår i: Expected Performance of the ATLAS Experiment: Detector, Trigger and Physics, Geneva: CERN , 2008Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The discovery of a charged Higgs boson would be tangible proof of physics beyond the Standard Model. This note presents the ATLAS potential for discovering a charged Higgs boson, utilizing five different final states of the signal arising from the three dominating fermionic decay modes of the charged Higgs boson. The search covers the region below the top quark mass, taking into account the present experimental constraints, the transition region with a charged Higgs boson mass of the order of the top quark mass, and the high-mass region with a charged Higgs boson mass up to 600 GeV. All studies are performed with a realistic simulation of the detector response including all three trigger levels and taking into account all dominant systematic uncertainties. Results are given in terms of discovery and exclusion contours for each channel individually and for all channels combined, showing that the ATLAS experiment is capable of detecting the charged Higgs boson in a significant fraction of the (tanb, mH±) parameter space with its first 10 fb−1 of data. The so-called intermediate tanb region (around tanb = 7) is experimentally hard to reach but exclusion sensitivity is given in this area.

    sted, utgiver, år, opplag, sider
    Geneva: CERN, 2008
    Emneord
    ATLAS Charged Higgs Boson Searches
    Identifikatorer
    urn:nbn:se:uu:diva-110660 (URN)978-92-9083-321-5 (ISBN)
    Tilgjengelig fra: 2009-11-21 Laget: 2009-11-21 Sist oppdatert: 2011-03-04
    3. An Investigation of the ATLAS Discovery Potential for Charged Higgs Bosons in the Tau Decay Mode Applying an Iterative Discriminant Analysis Method
    Åpne denne publikasjonen i ny fane eller vindu >>An Investigation of the ATLAS Discovery Potential for Charged Higgs Bosons in the Tau Decay Mode Applying an Iterative Discriminant Analysis Method
    2008 (engelsk)Rapport (Annet vitenskapelig)
    Abstract [en]

    Charged Higgs bosons are predicted in models beyond the Standard Model, for example in two-Higgs-doublet models and specifically in Minimal Supersymmetric extensions of the Standard Model (MSSM). We have applied an Iterative Discriminant Analysis (IDA) method with the aim to study how the use of this multivariate method can improve on the sequential-cut-based method. The IDA method has been used to optimize the signal efficiency and background rejection in a charged Higgs boson discovery analysis for Higgs masses in the range 165 GeV to 600 GeV. The analysis is based on high-statistics Monte Carlo data and a fast detector simulation. The performance of the IDA results is compared with that of a recent sequential-cut-based analysis.

    Publisher
    s. 21
    Serie
    CDS
    Emneord
    ATLAS Charged Higgs Boson IDA
    Identifikatorer
    urn:nbn:se:uu:diva-110661 (URN)
    Tilgjengelig fra: 2009-11-21 Laget: 2009-11-21 Sist oppdatert: 2011-03-04bibliografisk kontrollert
    4. ATLAS Tau Identification in High-Multiplicity Environments
    Åpne denne publikasjonen i ny fane eller vindu >>ATLAS Tau Identification in High-Multiplicity Environments
    2009 (engelsk)Rapport (Annet vitenskapelig)
    Abstract [en]

    The tau identification in two distinct high-multiplicity environments, pile-up and ttbar events, is investigated. The tau ID performance in such environments is known to be degraded. It is shown that it is necessary to adjust the tau ID quality cut in order to reach a working point in terms of tau efficiency versus jet rejection comparable to more frequently investigated and cleaner types of events like Z->tautau and W->taunu. Three different ways of recovering performance and robustness are investigated: Firstly, the usage of dedicated probability density functions as input to the tau likelihood method is tested, obtained from Z->tautau events with pile-up and ttbar events. Effects are generally small, except for high-pT tau jets in ttbar events. Secondly, it is investigated whether likelihood input variables can be removed without reducing performance (to increase robustness and reduce systematic uncertainties), and thirdly, whether adding new variables or replacing existing variables with new variables can lead to increased performance in terms of jet rejection at fixed tau efficiency. It is shown that several variables are redundant for tau identification in high-multiplicity environments. At least one variable is identified which can efficiently replace one of the existing variables in high-multiplicity events, namely the fraction of energy deposited in a wider isolation cone than used by the default tau identification.

    Publisher
    s. 31
    Emneord
    ATLAS Tau Identification
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-110770 (URN)
    Tilgjengelig fra: 2009-11-24 Laget: 2009-11-24 Sist oppdatert: 2012-10-10bibliografisk kontrollert
    5. Embedding Technique for the ttbar Background Estimation in Charged Higgs Boson Searches
    Åpne denne publikasjonen i ny fane eller vindu >>Embedding Technique for the ttbar Background Estimation in Charged Higgs Boson Searches
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Standard Model-like decays of a top quark pair with tau leptons are the dominant background for most charged Higgs boson searches. It is shown that the background can be emulated starting from a pure ttbar->bmunu bW sample by replacing tracks and calorimeter cells on an ESD (Event Summary Data) level in close vicinity to the muon with those of a simulated tau lepton. ATLAS reconstruction algorithms are then re-run to provide higher-level objects, eliminating the need of ad-hoc corrections to the missing energy. Relevant distributions like top quark invariant masses, tau jet properties and missing transverse energy can be reproduced within a 10% level.

    Emneord
    ATLAS Embedding Charged Higgs ttbar tau
    Identifikatorer
    urn:nbn:se:uu:diva-110771 (URN)
    Tilgjengelig fra: 2009-11-24 Laget: 2009-11-24 Sist oppdatert: 2012-10-10
    6. Grid interoperability: joining grid information systems
    Åpne denne publikasjonen i ny fane eller vindu >>Grid interoperability: joining grid information systems
    2007 (engelsk)Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 119, nr 6, s. 062030-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A grid is defined as being 'coordinated resource sharing and problem solving in dynamic, multi-institutional virtual organizations'. Over recent years a number of grid projects, many of which have a strong regional presence, have emerged to help coordinate institutions and enable grids. Today, we face a situation where a number of grid projects exist, most of which are using slightly different middleware. Grid interoperation is trying to bridge these differences and enable Virtual Organizations to access resources at the institutions independent of their grid project affiliation. Grid interoperation is usually a bilateral activity between two grid infrastructures. Recently within the Open Grid Forum, the Grid Interoperability Now (GIN) Community Group is trying to build upon these bilateral activities. The GIN group is a focal point where all the infrastructures can come together to share ideas and experiences on grid interoperation. It is hoped that each bilateral activity will bring us one step closer to the overall goal of a uniform grid landscape. A fundamental aspect of a grid is the information system, which is used to find available grid services. As different grids use different information systems, interoperation between these systems is crucial for grid interoperability. This paper describes the work carried out to overcome these differences between a number of grid projects and the experiences gained. It focuses on the different techniques used and highlights the important areas for future standardization.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-110772 (URN)10.1088/1742-6596/119/6/062030 (DOI)
    Konferanse
    CHEP07
    Merknad
    Proceedings of CHEP07Tilgjengelig fra: 2009-11-24 Laget: 2009-11-24 Sist oppdatert: 2017-12-12bibliografisk kontrollert
  • 153. Folsom, C. P.
    et al.
    Wade, G. A.
    Kochukhov, Oleg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Alecian, E.
    Catala, C.
    Bagnulo, S.
    Landstreet, J. D.
    Hanes, D. A.
    Magnetic, chemical and rotational properties of the Herbig Ae/Be binary system HD 721062008Inngår i: Contributions of the Astronomical Observatory Skalnaté Pleso, ISSN 1335-1842, Vol. 38, nr 2, s. 245-250Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recently, strong, globally-ordered magnetic fields have been detected in some Herbig Ae and Be (HAeBe) stars, suggesting a possible evolutionary connection to main sequence magnetic chemically peculiar Ap and Bp stars. We have undertaken a detailed study of the binary system HD 72106, which contains a B9 magnetic primary and a HAeBe secondary, using the ESPaDOnS spectropolarimeter mounted on the CFHT. A careful analysis of the very young primary reveals that it has an approximately dipolar magnetic field geometry, strong chemical peculiarities, and strong surface chemical abundance inhomogeneities. Thus the primary is very similar to an Ap/Bp star despite having completed less then 1.5% of its main sequence life, and possible still being on the pre-main sequence. In contrast, a similar analysis of the secondary reveals solar chemical abundances and no magnetic field.

  • 154. Fossati, L.
    et al.
    Bagnulo, S.
    Landstreet, J.
    Wade, G.
    Kochukhov, Oleg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Monier, R.
    Weiss, W.
    Gebran, M.
    The effect of rotation on the abundances of the chemical elements of the A-type stars in the Praesepe cluster2008Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 483, nr 3, s. 891-902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims. We study how chemical abundances of late B-, A-, and early F-type stars evolve with time, and we search for correlations between the abundance of chemical elements and other stellar parameters, such as effective temperature and upsilon sin i.

    Methods. We observed a large number of B-, A-, and F-type stars belonging to open clusters of different ages. In this paper we concentrate on the Praesepe cluster (log t = 8.85), for which we have obtained high-resolution, high signal-to-noise ratio spectra of sixteen normal A- and F-type stars and one Am star, using the SOPHIE spectrograph of the Observatoire de Haute-Provence. For all the observed stars, we derived fundamental parameters and chemical abundances. In addition, we discuss another eight Am stars belonging to the same cluster, for which the abundance analysis had been presented in a previous paper. Results. We find a strong correlation between the peculiarity of Am stars and upsilon sin i. The abundance of the elements underabundant in Am stars increases with upsilon sin i, while it decreases for the overabundant elements. Chemical abundances of various elements appear correlated with the iron abundance.

  • 155. Fossati, L.
    et al.
    Bagnulo, S.
    Monier, R.
    Khan, S. A.
    Kochukhov, Oleg
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Landstreet, J. D.
    Wade, G. A.
    Weiss, W. W.
    Chemical evolution of A- and B-type stars in open clusters: observed abundances vs. diffusion models2008Inngår i: Contributions of the Astronomical Observatory Skalnaté Pleso, ISSN 1335-1842, Vol. 38, nr 2, s. 123-128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have decided to address the problem of how abundances and peculiarities change during main sequence evolution. We have setup a program to measure the atmospheric abundance patterns from tens of A-type star members of clusters of different ages, and compare the results with theory predictions. In this paper we present the overall project and we focus on the results obtained for a sample of Am stars of the Praesepe cluster (log t = 8.85 +/- 0.15; Gonzalez-Garcia et al., 2006). We have obtained spectra for eight Am stars, two normal A-type stars and one blue straggler, that are probable members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements. For seven stars we also obtained spectra in circular polarisation and applied the LSD technique to measure the mean longitudinal magnetic field. We have found good agreement between abundance predictions of diffusion models and measured abundances, except for Na and S. Li appears to be overabundant in three stars of our sample. No magnetic field was detected in any of the analysed stars.

  • 156.
    Freyhult, Lisa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Kruczenski, Martin
    Purdue University.
    Tirziu, Alin
    Purdue University.
    Spiky strings in the SL(2) Bethe Ansatz at strong coupling from AdS/CFT2009Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 7, s. 038-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study spiky strings in the context of the SL(2) Bethe ansatz equations. We find an asymmetric distribution of Bethe roots along one cut that determines the all loop anomalous dimension at leading and subleading orders in a large S expansion. At leading order in strong coupling (large lambda) we obtain that the energy of such states is given, in terms of the spin S and the number of spikes n by E-S=n sqrt{lambda}/(2 pi) (ln 16 pi S/(n sqrt{lambda})+ ln sin (pi/n) - 1)+ O(ln S/S). This result matches perfectly the same expansion obtained from the known spiky string classical solution. We then discuss a two cut spiky string Bethe root distribution at one-loop in the SL(2) Bethe ansatz. In this case we find a limit where n goes to infinity, keeping (E+S)/n^2, (E-S)/n, J/n fixed. This is the one loop version of a limit previously considered in the context of the string classical solutions in AdS5 x S5. In that case it was related to a string solution in the AdS pp-wave background.

  • 157.
    Freyhult, Lisa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Rej, Adam
    Staudacher, Matthias
    A generalized scaling function for AdS/CFT2008Inngår i: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, E-ISSN 1742-5468, s. P07015-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study a refined large spin limit for twist operators in the sl(2) sector of AdS/CFT. We derive a novel non-perturbative equation for the generalized two-parameter scaling function associated with this limit, and analyze it for weak coupling. It is expected to smoothly interpolate between weakly coupled gauge theory and string theory for strong coupling.

  • 158.
    Freyhult, Lisa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Zieme, Stefan
    AEI, Potsdam.
    The virtual scaling function of AdS/CFT2009Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 79, nr 10, s. 105009-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We write an integral equation that incorporates finite corrections to the large spin asymptotics of N=4 SYM twist operators from the non-linear integral equation. We show that these corrections are an all-loop result, not affected by wrapping effects, and agree, after determining the strong coupling expansion, with string theory predictions.

  • 159.
    Freytag, Bernd
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Höfner, Susanne
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Astronomi och rymdfysik.
    Three-dimensional simulations of the atmosphere of an AGB star2008Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 483, nr 2, s. 571-583Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Winds of asymptotic giant branch stars are assumed to be driven by radiation pressure on dust. Previously, this process has been modeled with detailed time-dependent simulations of atmospheres and winds assuming spherically symmetric flows. In such models kinetic energy is injected by a variable inner boundary ("piston") simulating the effects of stellar pulsation. However, the dynamical processes in these atmospheres - convection and pulsations - are actually three-dimensional. Aims. We present and analyze first 3D radiation hydrodynamics simulations of the convective interior and the atmosphere of a typical AGB star. In particular, we check whether the piston description in the 1D wind models is compatible with the 3D results. Methods. We used two different RHD codes, one (CO5BOLD) to produce 3D models of the outer convective envelope and the inner atmosphere of an AGB star, the other to describe the atmosphere and the wind acceleration region, including dust formation and non-grey radiative transfer, but assuming spherically symmetric flows. From the movements of stellar surface layers in the 3D models, we derived a description for the variable inner boundary in the 1D models. Results. The 3D models show large convection cells and pulsations that give rise to roughly spherically expanding shock waves in the atmosphere, levitating material into regions which are cool enough to allow for dust formation. The atmospheric velocity fields have amplitudes and time scales close to the values that are necessary to start dust formation in the 1D wind models. Conclusions. The convection cells in the 3D simulations are so large that the associated shock fronts appear almost spherical, justifying the assumption of spherical symmetry and the use of a piston boundary condition in the context of wind models. Nevertheless, certain non-radial structures exist in the dust shell developing in the 3D simulations which should be detectable with current interferometric techniques.

  • 160.
    Fäldt, Göran
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Tengblad, Ulla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Coulomb-nuclear interference in pion-nucleus bremsstrahlung2009Inngår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 79, nr 1, s. 014607-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pion-nucleus bremsstrahlung offers a possibility of measuring the structure functions of pion-Compton scattering from a study of the small-momentum-transfer region where the bremsstrahlung reaction is dominated by the single-photon-exchange mechanism. The corresponding cross-section distribution is characterized by a sharp peak at small momentum transfers. But there is also a hadronic contribution that is smooth and constitutes an undesired background. In this article the modification of the single-photon-exchange amplitude by multiple Coulomb scattering is investigated as well as the Coulomb-nuclear interference term.

  • 161.
    Fäldt, Göran
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Tengblad, Ulla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Pion Compton scattering and bremsstrahlung2008Inngår i: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 78, nr 1, s. 014606-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pion polarizability functions are structure functions of pion Compton scattering. They can be assessed in high-energy pion-nucleus bremsstrahlung reactions, pi(-)+A -> ;pi(-)+gamma+A. We present numerical expectations for pion-nucleus bremsstrahlung cross sections in the Coulomb region, i.e., the small-angle region where the nuclear scattering is dominated by the Coulomb interaction. We investigate the prospects of measuring the polarizability functions for pion-Compton center-of-momentum energies from threshold up to 1 GeV. A meson-exchange model is used for the pion Compton amplitude.

  • 162.
    Gabrielli, Emidio
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Institutionen för kärn- och partikelfysik, Högenergifysik.
    Mele, Barbara
    Institutionen för kärn- och partikelfysik, Högenergifysik.
    Rathsman, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Institutionen för kärn- och partikelfysik, Högenergifysik.
    Higgs boson plus photon production at the LHC: a clean probe of the b-quark parton densities2008Inngår i: Physical Review D, Vol. 77, s. 0105007-Artikkel i tidsskrift (Fagfellevurdert)
  • 163. Gabrielli, Emidio
    et al.
    Mele, Barbara
    Rathsman, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Higgs-boson-plus-photon production at the CERN Large Hadron Collider: A clean probe of the b-quark parton densities2008Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 77, nr 1, s. 015007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Higgs boson production in association with a high p(T) photon at the CERN Large Hadron Collider is analyzed, in the framework of the MSSM model, for the heavier neutral Higgs bosons. The request of an additional photon in the exclusive Higgs boson final state selects b-quark pairs among the possible initial partonic states, since gluon-gluon initial states are not allowed by C-parity conservation. Hence, the measurement of cross sections for neutral Higgs boson plus photon production can provide a clean probe of the b-quark density in the proton as well as of the b-quark Yukawa coupling. The suppression of the production rates by the b-quark electromagnetic coupling can be compensated by the enhanced Higgs boson Yukawa coupling to b's in the large tan beta regime. The Higgs boson decay into a tau-lepton pair is considered, and irreducible backgrounds with corresponding signal significances are evaluated.

  • 164.
    Gatu Johnson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Conroy, Sean
    Andersson Sundén, Erik
    Cecconello, Marco
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ericsson, Göran
    Hellesen, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Gherendi, Mihaela
    Association EURATOM-MEdC, National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania.
    Hjalmarsson, Anders
    Murari, Andrea
    Consorzio RFX-Associazione EURATOM ENEA per la Fusione, I-35127 Padova, Italy.
    Popovichev, Sergei
    EURATOM/CCFE Association, Culham Science Centre, Abingdon, United Kingdom.
    Ronchi, Emanuele
    Weiszflog, Matthias
    Zoita, Liviu Vasile
    Association EURATOM-MEdC, National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania.
    Modeling and TOFOR measurements of scattered neutrons at JETManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this paper, the scattered and direct neutron fluxes in the line-of-sight of the TOFOR neutron spectrometer at JET are simulated and the simulations compared with measurement results. The Monte Carlo code MCNPX is used in the simulations, with a vessel material composition obtained from the JET drawing office and neutron emission profiles calculated from TRANSP simulations of beam ion density profiles. The MCNPX simulations show that the material composition of the scattering wall has a large effect on the shape of the scattered neutron spectrum. Neutron source profile shapes as well as radial and vertical source displacements in the TOFOR line-of-sight are shown to only marginally affect the scatter, while having a larger impact on the direct neutron flux. A matrix of simulated scatter spectra for mono-energetic source neutrons is created which is folded with an approximation of the source spectrum for each JET pulse studied to obtain a scatter component for use in the data analysis. The scatter components thus obtained are shown to describe the measured data. It is also demonstrated that the scattered flux is approximately constant relative to the total neutron yield as measured with the JET fission chambers, while there is a larger spread in the direct flux, consistent with simulations. The simulated effect on the integrated scattered/direct ratio of an increase with movements outward along the radial direction and a drop at higher values of the vertical plasma position is also reproduced in the measurements. Finally, the quantitative agreement found in scatter/direct ratios between simulations (0.185±0.005) and measurements (0.187±0.050) serves as a solid benchmark of the MCNPX model used.

  • 165.
    Gatu Johnson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Giacomelli, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hjalmarsson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Källne, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Weiszflog, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Andersson Sundén, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Conroy, Sean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ericsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hellesen, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ronchi, Emanuele
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Sjöstrand, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Gorini, G
    Tardocchi, M
    Combo, A
    Cruz, N
    Sousa, J
    Popovichev, S
    The 2.5-MeV neutron time-of-flight spectrometer TOFOR for experiments at JET2008Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 591, nr 2, s. 417-430Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A time-of-flight (TOF) spectrometer for measurement of the 2.5-MeV neutron emission from fusion plasmas has been developed and put into use at the JET tokamak. It has been optimized for operation at high rates (TOFOR) for the purpose of performing advanced neutron emission spectroscopy (NES) diagnosis of deuterium plasmas with a focus on the fuel ion motional states for different auxiliary heating scenarios. This requires operation over a large dynamic range, including high rates of > 100 kHz with a maximum value of 0.5 MHz for the TOFOR design. This paper describes the design principles and their technical realization. The performance is illustrated with recent neutron TOF spectra recorded for plasmas subjected to different heating scenarios. A true event count rate of 39 kHz has been achieved at about a tenth of the expected neutron yield limit of JET, giving a projected maximum of 400 kHz at peak JET plasma yield. This means that the count rate capability for NES diagnosis of D plasmas has been improved more than an order of magnitude. Another important performance factor is the spectrometer bandwidth, where data have been acquired and analyzed successfully with a response function for neutrons over the energy range 1 to > 5 MeV. The implications of instrumental advancement represented by TOFOR are discussed.

  • 166.
    Gatu Johnson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Giacomelli, Luca
    Hjalmarsson, Anders
    Weiszflog, Matthias
    Andersson Sundén, Erik
    Conroy, Sean
    Ericsson, Göran
    Hellesen, Carl
    Källne, Jan
    Ronchi, Emanuele
    Gorini, Giuseppe
    EURATOM-ENEA-CNR Association, Instituto di Fisica del Plasma, I-20126 Milan, Italy.
    Tardocchi, Marco
    Murari, Andrea
    EURATOM-ENEA-CNR Association, Consorzio RFX, I.35127 Padua, Italy.
    Popovichev, Sergei
    EURATOM-UKAEA Association, JET, Culham Science Centre, Abingdon, Oxfordshire, GB OX14 3DB, United Kingdom.
    Sousa, Jorge
    Associação EURATOM/Instituto Superior Técnico (IST), Centro de Fusão Nuclear, Avenida Rovisco Pais 1, P1049-001 Lisboa, Portugal.
    Pereira, Rita
    Combo, Alvaro
    Cruz, Nuno
    The TOFOR neutron spectrometer and its first use at JET2006Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, nr 10E702, s. 1-3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A time-of-flight neutron spectrometer (TOFOR) has been developed to measure the 2.45  MeV  d+d3He+n neutron emission from D plasmas. The TOFOR design features the capability to operate at high rates in the 100  kHz range, data collection with fast time digitizing and storing, and monitoring of the signals from the scintillation detectors used. This article describes the principles of the instrument and its installation at JET and presents preliminary data to illustrate the TOFOR performance as a neutron emission spectroscopy diagnostic.

  • 167.
    Gatu Johnson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hellesen, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Andersson Sundén, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Cecconello, Marco
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Conroy, Sean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ericsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Gorini, Giuseppe
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Kiptily, Vasily
    Euratom / UKAEA Fusion Association, Culham Science Centre, Abingdon, United Kingdom.
    Nocente, Massimo
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Pinches, Simon
    Euratom / UKAEA Fusion Association, Culham Science Centre, Abingdon, United Kingdom.
    Ronchi, Emanuele
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Sharapov, Sergei
    Euratom / UKAEA Fusion Association, Culham Science Centre, Abingdon, United Kingdom.
    Sjöstrand, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Tardocchi, Marco
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Weiszflog, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Neutron emission from beryllium reactions in JET deuterium plasmas with 3He minority2010Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 4, s. 045005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent fast ion studies at JET involve ion cyclotron resonance frequency (ICRF) heating tuned to minority He-3 in cold deuterium plasmas, with beryllium evaporation in the vessel prior to the session. During the experiments, the high-resolution neutron spectrometer TOFOR was used to study the energy spectrum of emitted neutrons. Neutrons of energies up to 10MeV, not consistent with the neutron energy spectrum expected from d(d,n)He-3 reactions, were observed. In this paper, we interpret these neutrons as a first-time observation of a Be-9(He-3, n)C-11 neutron spectrum in a tokamak plasma, a conclusion based on a consistent analysis of experimental data and Monte Carlo simulations. Be-9(a, n)C-12 and Be-9(p, n)B-9 reactions are also simulated for p and a fusion products from d(He-3, a) p reactions; these two-step processes are seen to contribute on a level of about 10% of the single-step process in Be-9(He-3, n) C-11. Contributions to the total neutron yield from the Be-9(3He, n)C-11 reaction are found to be in the range 13 +/- 3 to 57 +/- 5%. We demonstrate how TOFOR can be used to simultaneously (i) probe the deuterium distribution, providing reliable measurements of the bulk deuterium temperature, here in the range 3.2 +/- 0.4 to 6.3 +/- 1.0 keV and (ii) provide an estimate of the beryllium concentration (in the range 0.48 +/- 0.17 to 6.4 +/- 1.7% of n(e) assuming T-3He = 300 keV). The observation of Be-9 related neutrons is relevant in view of the upcoming installation of a beryllium-coated ITER-like wall on JET and for ITER itself. An important implication is possible neutron-induced activation of the ITER vessel during the low-activation phase with ICRF heating tuned to minority He-3 in hydrogen plasmas.

  • 168.
    Gatu Johnson, Maria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hellesen, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Andersson Sundén, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Cecconello, Marco
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Conroy, Sean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ericsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Gorini, Giuseppe
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Nocente, Massimo
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Ronchi, Emanuele
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Tardocchi, Marco
    Physics Department, Milano-Bicocca University, and Istituto di Fisica del Plasma del CNR, Milan, Italy (EURATOM-ENEA-CNR Association).
    Weiszflog, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Neutron emission levels during the ITER zero activation phase2010Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, nr 8, s. 084020-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In recent experiments at JET, a contribution to the neutron emission from reactions between beryllium and 3He, 4He and H has been identified. With the beryllium walled planned for ITER, this raises the question of possible neutron activation during the ITER zero activation phase. Here, we estimate the neutron emission rates for various heating scenarios foreseen for this ITER phase using Monte Carlo simulations. The emission is seen to be strongly dependent on the scenario chosen and the assumptions involved. We find that fundamental minority heating can contribute on the scale of low temperature deuterium plasmas, depending on minority concentration and ICRH power applied. Harmonic ICRH leads to production of tails that can give rise to significant neutron emission rates, while rates from hydrogen beams will be near zero. Better knowledge of the zero activation phase conditions, and more sophisticated ICRH codes, would be needed to give exact rate predictions. We conclude that rates from so-called zero activation plasmas will be significantly lower than expected for the DD or DT phases, but far from zero.

  • 169. Gherendi, M.
    et al.
    Kiptly, V.
    Zoita, V.
    Conroy, Sean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Edlington, T.
    Falie, D.
    Murari, A.
    Pantea, A.
    Popovichev, S.
    Santala, M.
    Soare, S.
    Super-heated fluid detectors for neutron measurements at JET2008Inngår i: Journal of Optoelectronics and Advanced Materials, ISSN 1454-4164, E-ISSN 1841-7132, Vol. 10, nr 8, s. 2092-2094Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work we report the results of a first series of neutron measurements carried out at JET during the last experimental campaigns (C17-C19) using super-heated fluid detectors (SHFD's). The SHFD's were located in the neutron beam propagating along a collimated vertical line-of-sight, above the TOFOR neutron time-of-flight spectrometer (KM11 diagnostics). The radial distribution of the neutron fluence in the neutron beam was obtained with less than one cm spatial resolution. The neutron spectrum in the neutron beam was obtained over a broad energy range (six energy bins, from 10 keV to 20 MeV).

  • 170.
    Giacomelli, L
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hjalmarsson, A
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Källne, J
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Hellesen, C
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Tardocchi, M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Goroni, G
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Van Eester, D
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Lerche, E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Johnson, T
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Kiptily, V
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Conroy, S
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Andersson Sundén, E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ericsson, G
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Gatu Johnson, M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Ronchi, E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Sjöstrand, H
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Weiszflog, M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Neutron Emission Spectroscopy Results for ITB and Mode Conversion ICRH Experiments at JET2008Inngår i: Rev. Sci. Instr., submitted, 2008Konferansepaper (Fagfellevurdert)
  • 171.
    Giacomelli, L.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Hjalmarsson, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Kallne, J.
    Hellesen, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Tardocchi, M.
    Gorini, G.
    Van Eester, D.
    Lerche, E.
    Johnson, T.
    Kiptily, V.
    Conroy, Sean
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Sunden, E. Andersson
    Ericsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Johnson, Maria Gatu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Sjöstrand, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Weiszflog, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Neutron emission spectroscopy results for internal transport barrier and mode conversion ion cyclotron resonance heating experiments at JET2008Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 79, nr 10, s. 10E514-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of ion cyclotron resonance heating (ICRH) on (He-3)D plasmas at JET was studied with the time of flight optimized rate (TOFOR) spectrometer dedicated to 2.5 MeV dd neutron measurements. In internal transport barrier (ITB) plasma experiments with large He-3 concentrations (X(He-3)>15%) an increase in neutron yield was observed after the ITB disappeared but with the auxiliary neutral beam injection and ICRH power still applied. The analysis of the TOFOR data revealed the formation of a high energy (fast) D population in this regime. The results were compared to other mode conversion experiments with similar X(He-3) but slightly different heating conditions. In this study we report on the high energy neutron tails originating from the fast D ions and their correlation with X(He-3) and discuss the light it can shed on ICRH-plasma power coupling mechanisms.

  • 172. Giacomelli, Luca
    et al.
    Andersson Sundén, Erik
    Källne, Jan
    Popovichev, Sergey
    Ronchi, Emanuele
    Weiszflog, Matthias
    Tardocchi, Marco
    EFDA contributors, JET
    Murari, Andrea
    Conroy, Sean
    Ericsson, Göran
    Gatu Johnson, Maria
    Sjöstrand, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Gorini, Giuseppe
    Hellesen, Carl
    Hjalmarsson, Anders
    Development and Characterization of the Proton Recoil Detector for the MPRu Neutron Spectrometer2006Inngår i: Review of Scientific Instruments, Vol. 77, s. 10E 708-Artikkel i tidsskrift (Fagfellevurdert)
  • 173.
    Giangreco Marotta Puletti, Valentina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Aspects of quantum integrability for pure spinor superstring in AdS5 × S52008Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 09, s. 070-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider the monodromy matrix for the pure spinor IIB superstring on AdS5 × S5 at leading order at strong coupling, in particular its variation under an infinitesimal and continuous deformation of the contour. Such variation is equivalent to the insertion of a local operator. Demanding the BRST-closure for such an operator rules out its existence, implying that the monodromy matrix remains contour-independent at the first order in perturbation theory. Furthermore we explicitly compute the field strength corresponding to the flat connections up to leading order and directly check that it is free from logarithmic divergences. The absence of anomaly in the coordinate transformation of the monodromy matrix and the UV-finiteness of the curvature tensor finally imply the integrability of the pure spinor superstring at the first order.

  • 174.
    Giangreco Marotta Puletti, Valentina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    On string integrability: A journey through the two-dimensional hidden symmetries in the AdS/CFT dualities2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    One of the main topics in the modern String Theory are the conjectured string/gauge (AdS/CFT) dualities. Proving such conjectures is extremely difficult since the gauge and string theory perturbative regimes do not overlap. In this perspective, the discovery of infinitely many conserved charges, i.e. the integrability, in the planar AdS/CFT has allowed us to reach immense progresses in understanding and confirming the duality.The first part of this thesis is focused on the gravity side of the AdS5/CFT4 duality: we investigate the quantum integrability of the type IIB superstring on AdS5 x S5. In the pure spinor formulation we analyze the operator algebra by computing the operator product expansion of the Maurer-Cartan currents at the leading order in perturbation theory. With the same approach at one loop order, we show the path-independence of the monodromy matrix which implies the charge conservation law, strongly supporting the quantum integrability of the string sigma-model. We also verify that the Lax pair field strength remains well-defined at one-loop order being free from UV divergences. The same string sigma-model is analyzed in the Green-Schwarz formalism in the near-flat-space (NFS) limit. Such a limit remarkably simplifies the string world-sheet action but still leaving interesting physics. We use the NFS truncation to show the factorization of the world-sheet S-matrix at one-loop order. This property defines a two-dimensional field theory as integrable: it is the manifestation of the higher conserved charges. Hence, we have explicitly checked their presence at quantum level. The second part is dedicated to the AdS4/CFT3 duality: in particular the type IIA superstring on AdS4 x CP3. We compute the leading quantum corrections to the string energies for string configurations with a large but yet finite angular momentum on CP3 and show that they match the conjectured all-loop Bethe Ansatz equations.

    Delarbeid
    1. Operator product expansion for pure spinor superstring on AdS5 x S5
    Åpne denne publikasjonen i ny fane eller vindu >>Operator product expansion for pure spinor superstring on AdS5 x S5
    2006 (engelsk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 10, s. 057-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The tree-level operator product expansion coefficients of the matter currents are calculated in the pure spinor formalism for type IIB superstring in the AdS5 × S5 background.

    Emneord
    AdS-CFT correspondence, Sigma models
    HSV kategori
    Forskningsprogram
    Teoretisk fysik
    Identifikatorer
    urn:nbn:se:uu:diva-107321 (URN)10.1088/1126-6708/2006/10/057 (DOI)000242714400033 ()
    Tilgjengelig fra: 2009-08-05 Laget: 2009-08-05 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    2. Factorized world-sheet scattering in near-flat AdS5×S5
    Åpne denne publikasjonen i ny fane eller vindu >>Factorized world-sheet scattering in near-flat AdS5×S5
    2008 (engelsk)Inngår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 792, nr 3, s. 228-256Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We show the factorization of the three-particle world-sheet S-matrix of AdS5×S5 superstring theory in the near-flat-space limit at one loop order. This is done by computing various scattering amplitudes from Feynman diagrams in the world-sheet theory. The knowledge of certain highest weight amplitudes allows us to fix all the freedom in the three-particle S-matrix, which we argue to be constrained up to four scalar functions due to the symmetries of the model. We demonstrate that these amplitudes are given by corresponding products of the known two-particle S-matrix elements, from which it follows that the scattering of any three world-sheet excitations factorizes. This provides an explicit and direct check of the quantum integrability of string theory in near-flat AdS5×S5 as it renders evidence for the existence of higher conserved charges. By computing further amplitudes we also obtain an indirect confirmation of the supersymmetries of the near-flat-space model.

    Emneord
    AdS/CFT correspondence, S-matrix, Integrability, Factorized scattering
    HSV kategori
    Forskningsprogram
    Fysik; Teoretisk fysik
    Identifikatorer
    urn:nbn:se:uu:diva-107322 (URN)10.1016/j.nuclphysb.2007.09.018 (DOI)000253102400002 ()
    Tilgjengelig fra: 2009-08-05 Laget: 2009-08-05 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    3. Finite-size corrections in the SU(2)×SU(2) sector of type IIA string theory on AdS4 x CP3
    Åpne denne publikasjonen i ny fane eller vindu >>Finite-size corrections in the SU(2)×SU(2) sector of type IIA string theory on AdS4 x CP3
    Vise andre…
    2009 (engelsk)Inngår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 810, nr 1-2, s. 150-173Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider finite-size corrections in the SU(2)×SU(2) sector of type IIA string theory on , which is the string dual of the recently constructed  superconformal Chern–Simons theory of Aharony, Bergman, Jafferis and Maldacena (ABJM theory). The string states we consider are in the  subspace of  with an angular momentum J on  being large. We compute the finite-size corrections using two different methods, one is to consider curvature corrections to the Penrose limit giving an expansion in1/J, the other by considering a low energy expansion in λ=λ/J2 of the string theory sigma-model, λ being the 't Hooft coupling of the dual ABJM theory. For both methods there are interesting issues to deal with. In the near-pp-wave method there is a  interaction term for which we use zeta-function regularization in order to compute the 1/J correction to the energy. For the low energy sigma-model expansion we have to take into account a non-trivial coupling to a non-dynamical transverse direction. We find agreement between the two methods. At order λ and , for small λ, our results are analogous to the ones for the SU(2) sector in type IIB string theory on AdS5×S5. Instead at order  there are interactions between the two two-spheres. We compare our results with the recently proposed all-loop Bethe ansatz of Gromov and Vieira and find agreement.

    Emneord
    string theory, integrability
    HSV kategori
    Forskningsprogram
    Teoretisk fysik
    Identifikatorer
    urn:nbn:se:uu:diva-107323 (URN)10.1016/j.nuclphysb.2008.10.020 (DOI)000262824200007 ()
    Tilgjengelig fra: 2009-08-05 Laget: 2009-08-05 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    4. Aspects of quantum integrability for pure spinor superstring in AdS5 × S5
    Åpne denne publikasjonen i ny fane eller vindu >>Aspects of quantum integrability for pure spinor superstring in AdS5 × S5
    2008 (engelsk)Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 09, s. 070-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We consider the monodromy matrix for the pure spinor IIB superstring on AdS5 × S5 at leading order at strong coupling, in particular its variation under an infinitesimal and continuous deformation of the contour. Such variation is equivalent to the insertion of a local operator. Demanding the BRST-closure for such an operator rules out its existence, implying that the monodromy matrix remains contour-independent at the first order in perturbation theory. Furthermore we explicitly compute the field strength corresponding to the flat connections up to leading order and directly check that it is free from logarithmic divergences. The absence of anomaly in the coordinate transformation of the monodromy matrix and the UV-finiteness of the curvature tensor finally imply the integrability of the pure spinor superstring at the first order.

    Emneord
    AdS-CFT correspondence, Superstring and Heterotic string
    HSV kategori
    Forskningsprogram
    teoretisk fysik
    Identifikatorer
    urn:nbn:se:uu:diva-107324 (URN)10.1088/1126-6708/2008/09/070 (DOI)000259699700067 ()
    Tilgjengelig fra: 2009-08-05 Laget: 2009-08-05 Sist oppdatert: 2017-12-13bibliografisk kontrollert
  • 175.
    Giangreco Marotta Puletti, Valentina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Operator product expansion for pure spinor superstring on AdS5 x S52006Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 10, s. 057-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tree-level operator product expansion coefficients of the matter currents are calculated in the pure spinor formalism for type IIB superstring in the AdS5 × S5 background.

  • 176.
    Giangreco Marotta Puletti, Valentina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Klose, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för teoretisk fysik.
    Ohlsson Sax, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för teoretisk fysik.
    Factorized world-sheet scattering in near-flat AdS5×S52008Inngår i: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 792, nr 3, s. 228-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show the factorization of the three-particle world-sheet S-matrix of AdS5×S5 superstring theory in the near-flat-space limit at one loop order. This is done by computing various scattering amplitudes from Feynman diagrams in the world-sheet theory. The knowledge of certain highest weight amplitudes allows us to fix all the freedom in the three-particle S-matrix, which we argue to be constrained up to four scalar functions due to the symmetries of the model. We demonstrate that these amplitudes are given by corresponding products of the known two-particle S-matrix elements, from which it follows that the scattering of any three world-sheet excitations factorizes. This provides an explicit and direct check of the quantum integrability of string theory in near-flat AdS5×S5 as it renders evidence for the existence of higher conserved charges. By computing further amplitudes we also obtain an indirect confirmation of the supersymmetries of the near-flat-space model.

  • 177.
    Grape, Sophie
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärnfysik.
    PWO Crystal Measurements and Simulation Studies of Anti-Hyperon Polarisation for PANDA2008Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The Gesellschaft für Schwerionenforschung (GSI) facility in Darmstadt, Germany, will be upgraded to accommodate a new generation of physics experiments. The future accelerator facility will be called FAIR and one of the experimentsat the site will be PANDA, which aims at performing hadron physics investigations by colliding anti-protons with protons. The licentiate thesis consistsof three sections related to PANDA. The first contains energy resolutionstudies of PbWO4 crystals, the second light yield uniformity studies of PbWO4 crystals and the third reconstruction of the lambda-bar-polarisation in the PANDA experiment.

    Two measurements of the energy resolution were performed at MAX-Lab in Lund, Sweden, with an array of 3x3 PbWO4 crystals using a tagged photon beam with energies between 19 and 56 MeV. For the April measurement, the crystals were cooled down to -15 degrees C and for the September measurement down to -25 degrees C. The measured relative energy resolution, /E, is decreasing from approximately 12% at 20 MeV to 7% at 55 MeV. In the standard energy resolution expression /E = a/ b/E c, the three parameters a, b and c seem to be strongly correlated and thus difficult to determine independently over this relative small energy range. The value of a was therefore fixed to that one would expect from Poisson statistics of the light collection yield (50 phe/MeV) and the results from fits were /E=0.45%/ 0.18%/EGeV 8.63% and /E = 0.45%/0.21%/EGeV 6.12% for the April and September measurements, respectively. The data from the September measurement was also combined with previous data from MAMI for higher energies, ranging from approximately 64 to 715 MeV. The global fit over the whole range of energies gave an energy resolution expression of /E = 1.6%/ 0.095%/EGeV 2.1%.

    Light yield uniformity studies of five PbWO4 crystals, three tapered and two non-tapered ones, have also been performed. The tapered crystals delivered a light output which increased with increasing distance from the Photo Multiplier Tube (PM tube). Black tape was put on different sides of one tapered crystals, far from the PM tube to try to get a more constant uniformity prole. It was seen that the light output profile depends on the position of the tape. Generally, the steep increase in light output at large distances from the PM tube could be damped.

    The third part of the thesis concerns the reconstruction of the lambdabar polarisation in the reaction . Events were generated using a modied generator from the PS185 experiment at LEAR. With a 100% polarisation perpendicular to the scattering plane, a polarisation of (99±1.8)% was reconstructed. Slight non-zero polarisations along the axis determined by the outgoing hyperon as well as the axis in the scattering plane, were also reconstructed. These were (4.1±2.1)% and (2.6±2.0)% respectively. From this investigation it was shown that the detector efficiency was not homogeneous and that slow pions are difficult to reconstruct.

  • 178.
    Grape, Sophie
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Studies of PWO Crystals and Simulations of the p̅p →Λ̅Λ, Λ̅Σ0 Reactions for the PANDA Experiment2009Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The thesis comprises investigations of two topics related to the PANDA experiment. The first part is dedicated to energy resolution and light yield uniformity studies of PWO crystals for the electromagnetic calorimeter. The second part of the thesis is dedicated to simulation studies of the p̅p→Λ̅Λ and the p̅p→Λ̅Σ0 channels.

    Photon response measurements with one 3×3 crystals matrix of rectangular crystals and one 5×5 matrix with tapered crystals have been performed at the MAX-Lab synchrotron facility in Lund, Sweden. Photon energies in the range of 13-84 MeV were used. GEANT4 simulations were performed in order to find the most suitable method for adding the energy contributions and for calibration purposes. The widths, σ, of the resulting experimental summed energy peaks were fitted using the Novosibirsk distribution. The results show that the electromagnetic shower at 84 MeV is completely contained in the 5×5 matrix. The widths (σ) for the summed energy peaks were determined.Studies of the uniformity of the light yield were performed for crystals of three different shapes and different wrapping materials. The light yield as a function of distance between the point of energy depositions and the PM tube, was shown to be closely related to the crystal shape and the wrapping material.

    The p̅p→Λ̅Λ channel was studies at beam momenta of 1.64 GeV/c, 4 GeV/c and 15 GeV/c, while p̅p→Λ̅Σ0 was studied at 4 GeV/c. In the simulations, both phase space differential cross-sections and experimental differential cross-sections from PS185 were used as input. The purpose of the simulations was to show that the reaction channels can be reconstructed in the detector. Special interest was paid to the polarisation and spin correlations of the hyperons. The result is that there is acceptance of cosθ angular range over the full momentum range of the HESR for both channels. Using isotropic differential cross-sections, the polarisation for Λ̅ and Σ0 as well as spin correlations between Λ̅Λ and Λ̅Σ0 can be well reconstructed. Using the differential cross-sections from PS185, the particles are more likely to go forwards in their respective directions in the CM-system, thus making reconstruction over the full angular range more difficult at high beam momenta.

     

  • 179.
    Grumiller, Daniel
    et al.
    Massachusetts Institute of Technology.
    Jackiw, Roman
    Massachusetts Institute of Technology.
    Johansson, Niklas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Canonical analysis of cosmological topologically massive gravity at the chiral pointManuskript (Annet vitenskapelig)
    Abstract [en]

    Wolfgang Kummer was a pioneer of two-dimensional gravity and a strong advocate of the first order formulation in terms of Cartan variables. In the present work we apply Wolfgang Kummer's philosophy, the `Vienna School approach', to a specific three-dimensional model of gravity, cosmological topologically massive gravity at the chiral point. Exploiting a new Chern-Simons representation we perform a canonical analysis. The dimension of the physical phase space is two per point, and thus the theory exhibits a local physical degree of freedom, the topologically massive graviton.

  • 180.
    Grumiller, Daniel
    et al.
    Center for Theoretical Physics, Massachusetts Institute of Technology.
    Johansson, Niklas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Consistent boundary conditions for cosmological topologically massive gravity at the chiral point2008Inngår i: International Journal of Modern Physics D, ISSN 0218-2718, Vol. 17, nr 13-14, s. 2367-2372Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show that cosmological topologically massive gravity at the chiral point allows not only Brown-Henneaux boundary conditions as consistent boundary conditions, but slightly more general ones which encompass the logarithmic primary found in 0805.2610 as well as all its descendants.

  • 181.
    Grumiller, Daniel
    et al.
    Center for Theoretical Physics, Massachusetts Institute of Technology.
    Johansson, Niklas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Teoretisk fysik.
    Instability in cosmological topologically massive gravity at the chiral point2008Inngår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 7, s. 134-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider cosmological topologically massive gravity at the chiral point with positive sign of the Einstein-Hilbert term. We demonstrate the presence of a negative energy bulk mode that grows linearly in time. Unless there are physical reasons to discard this mode, this theory is unstable. To address this issue we prove that the mode is not pure gauge and that its negative energy is time-independent and finite. The isometry generators L0 and 0 have non-unitary matrix representations like in logarithmic CFT. While the new mode obeys boundary conditions that are slightly weaker than the ones by Brown and Henneaux, its fall-off behavior is compatible with spacetime being asymptotically AdS3. We employ holographic renormalization to show that the variational principle is well-defined. The corresponding Brown-York stress tensor coincides with that of global AdS3. Finally we address possibilities to eliminate the instability and prospects for chiral gravity.

  • 182. Guastalla, G
    et al.
    DiJulio, D D
    Górska, M
    CederkÀll, J
    Boutachkov, P
    Golubev, P
    Pietri, S
    Grawe, H
    Nowacki, F
    Algora, A
    Ameil, F
    Arici, T
    Atac, A
    Bentley, M A
    Blazhev, A
    Bloor, D
    Brambilla, S
    Braun, N
    Camera, F
    Pardo, C Domingo
    Estrade, A
    Farinon, F
    Gerl, J
    Goel, N
    Grȩbosz, J
    Habermann, T
    Hoischen, R
    Jansson, K
    Jolie, J
    Jungclaus, A
    Kojouharov, I
    Knoebel, R
    Kumar, R
    Kurcewicz, J
    Kurz, N
    Lalović, N
    Merchan, E
    Moschner, K
    Naqvi, F
    Singh, B S Nara
    Nyberg, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Kärnfysik.
    Nociforo, C
    Obertelli, A
    PfÃŒtzner, M
    Pietralla, N
    Podolyák, Z
    Prochazka, A
    Ralet, D
    Reiter, P
    Rudolph, D
    Schaffner, H
    Schirru, F
    Scruton, L
    Swaleh, T
    Taprogge, J
    Wadsworth, R
    Warr, N
    Weick, H
    Wendt, A
    Wieland, O
    Winfield, J S
    Wollersheim, H J
    Analysis and results of the 104 Sn Coulomb excitation experiment2014Inngår i: Journal of Physics: Conference Series, Vol. 533, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The analysis of the Coulomb excitation experiment conducted on 104 Sn required a strict selection of the data in order to reduce the large background present in the γ-ray energy spectra and identify the γ-ray peak corresponding to the Coulomb excitation events. As a result the B(E2; 0 + → 2 + ) value could be extracted, which established the downward trend towards 100 Sn and therefore the robustness of the N=Z=50 core against quadrupole excitations.

  • 183. Guchait, M.
    et al.
    Mahmoudi, F.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Sridhar, K.
    Associated production of a Kaluza-Klein excitation of a gluon with a t(t)over-bar pair at the LHC2008Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 666, nr 4, s. 347-351Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In certain model-realizations of the Randall-Sundrum scenario, the Kaluza-Klein (KK) excitations of the gluon, g(KK) have enhanced couplings to right-handed top quarks. In the absence of a ggg(KK) coupling in these models, the single production of a g(KK) from an initial gg state is not possible. The search for other production mechanisms at the LHC. therefore, becomes important. We suggest that the associated production of a g(KK) with a t (t) over bar pair is such a mechanism. Our parton-level study, which neglects detection efficiencies, shows that through this process the LHC can probe KK gluon masses in the range of 2.8-3.0 TeV.

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