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  • 1. Chatrchyan, S
    Alignment of the CMS Muon System with Cosmic-Ray and Beam-Halo Muons2010In: JINST, Vol. 5Article in journal (Refereed)
  • 2. Chatrchyan, S
    Alignment of the CMS Silicon Tracker during Commissioning with Cosmic Rays2010In: JINST, Vol. 5Article in journal (Refereed)
  • 3. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Aligning the CMS Muon Chambers with the Muon Alignment System during an Extended Cosmic Ray Run2010In: journal of instumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The alignment system for the muon spectrometer of the CMS detector comprises three independent subsystems of optical and analog position sensors. It aligns muon chambers with respect to each other and to the central silicon tracker. System commissioning at full magnetic field began in 2008 during an extended cosmic ray run. The system succeeded in tracking muon detector movements of up to 18 mm and rotations of several milliradians under magnetic forces. Depending on coordinate and subsystem, the system achieved chamber alignment precisions of 140–350 μm and 30–200 μrad, close to the precision requirements of the experiment. Systematic errors on absolute positions are estimated to be 340–590 μm based on comparisons with independent photogrammetry measurements.

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  • 4. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Calibration of the CMS Drift Tube Chambers and Measurement of the Drift Velocity with Cosmic Rays2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    This paper describes the calibration procedure for the drift tubes of the CMS barrel muon system and reports the main results obtained with data collected during a high statistics cosmic ray data-taking period. The main goal of the calibration is to determine, for each drift cell, the minimum time delay for signals relative to the trigger, accounting for the drift velocity within the cell. The accuracy of the calibration procedure is influenced by the random arrival time of the cosmic muons relative to the LHC clock cycle. A more refined analysis of the drift velocity was performed during the offline reconstruction phase, which takes into account this feature of cosmic ray events

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  • 5. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    CMS Data Processing Workflows during an Extended Cosmic Ray Run2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The CMS Collaboration conducted a month-long data taking exercise, the Cosmic Run At Four Tesla, during October-November 2008, with the goal of commissioning the experiment for extended operation. With all installed detector systems participating, CMS recorded 270 million cosmic ray events with the solenoid at a magnetic field strength of 3.8 T. This paper describes the data flow from the detector through the various online and offline computing systems, as well as the workflows used for recording the data, for aligning and calibrating the detector, and for analysis of the data.

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  • 6. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Commissioning of the CMS Experiment and the Cosmic Run at Four Tesla2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four Tesla in late 2008 in order to complete the commissioning of the experiment for extended operation. The operational lessons resulting from this exercise were addressed in the subsequent shutdown to better prepare CMS for LHC beams in 2009. The cosmic data collected have been invaluable to study the performance of the detectors, to commission the alignment and calibration techniques, and to make several cosmic ray measurements. The experimental setup, conditions, and principal achievements from this data-taking exercise are described along with a review of the preceding integration activities.

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  • 7. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Commissioning of the CMS High-Level Trigger with Cosmic Rays2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The CMS High-Level Trigger (HLT) is responsible for ensuring that data samples with potentially interesting events are recorded with high efficiency and good quality. This paper gives an overview of the HLT and focuses on its commissioning using cosmic rays. The selection of triggers that were deployed is presented and the online grouping of triggered events into streams and primary datasets is discussed. Tools for online and offline data quality monitoring for the HLT are described, and the operational performance of the muon HLT algorithms is reviewed. The average time taken for the HLT selection and its dependence on detector and operating conditions are presented. The HLT performed reliably and helped provide a large dataset. This dataset has proven to be invaluable for understanding the performance of the trigger and the CMS experiment as a whole.

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  • 8. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Identification and Filtering of Uncharacteristic Noise in the CMS Hadron Calorimeter2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.

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  • 9. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance and Operation of the CMS Electromagnetic Calorimeter2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75 848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented. Export citation and abstract

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  • 10. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance of CMS Hadron Calorimeter Timing and Synchronization using Test Beam, Cosmic Ray, and LHC Beam Data2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    This paper discusses the design and performance of the time measurement technique and of the synchronization systems of the CMS hadron calorimeter. Time measurement performance results are presented from test beam data taken in the years 2004 and 2006. For hadronic showers of energy greater than 100 GeV, the timing resolution is measured to be about 1.2 ns. Time synchronization and out-of-time background rejection results are presented from the Cosmic Run At Four Tesla and LHC beam runs taken in the Autumn of 2008. The inter-channel synchronization is measured to be within ±2 ns.

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  • 11. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance of the CMS Drift Tube Chambers with Cosmic Rays2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    Studies of the performance of the CMS drift tube barrel muon system are described, with results based on data collected during the CMS Cosmic Run at Four Tesla. For most of these data, the solenoidal magnet was operated with a central field of 3.8 T. The analysis of data from 246 out of a total of 250 chambers indicates a very good muon reconstruction capability, with a coordinate resolution for a single hit of about 260 μm, and a nearly 100% efficiency for the drift tube cells. The resolution of the track direction measured in the bending plane is about 1.8 mrad, and the efficiency to reconstruct a segment in a single chamber is higher than 99%. The CMS simulation of cosmic rays reproduces well the performance of the barrel muon detector.

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  • 12. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance Study of the CMS Barrel Resistive Plate Chambers with Cosmic Rays2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taking, which has recorded about 270 million events. The Resistive Plate Chamber system, which is part of the CMS muon detection system, was successfully operated in the full barrel. More than 98% of the channels were operational during the exercise with typical detection efficiency of 90%. In this paper, the performance of the detector during these dedicated runs is reported.

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  • 13. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Precise Mapping of the Magnetic Field in the CMS Barrel Yoke using Cosmic Rays2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The CMS detector is designed around a large 4 T superconducting solenoid, enclosed in a 12 000-tonne steel return yoke. A detailed map of the magnetic field is required for the accurate simulation and reconstruction of physics events in the CMS detector, not only in the inner tracking region inside the solenoid but also in the large and complex structure of the steel yoke, which is instrumented with muon chambers. Using a large sample of cosmic muon events collected by CMS in 2008, the field in the steel of the barrel yoke has been determined with a precision of 3 to 8% depending on the location

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  • 14. Chatrchyan, S
    et al.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Time Reconstruction and Performance of the CMS Electromagnetic Calorimeter2010In: Journal of Instrumentation, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The resolution and the linearity of time measurements made with the CMS electromagnetic calorimeter are studied with samples of data from test beam electrons, cosmic rays, and beam-produced muons. The resulting time resolution measured by lead tungstate crystals is better than 100 ps for energy deposits larger than 10 GeV. Crystal-to-crystal synchronization with a precision of 500 ps is performed using muons produced with the first LHC beams in 2008

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  • 15. Chatrchyan, S.
    et al.
    Gonzalez Suarez, Rebeca
    Univ Cantabria, CSIC, Inst Fis Cantabria IFCA, E-39005 Santander, Spain.
    White, A.
    Performance of the CMS drift-tube chamber local trigger with cosmic rays2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5, article id T03003Article in journal (Refereed)
    Abstract [en]

    The performance of the Local Trigger based on the drift-tube system of the CMS experiment has been studied using muons from cosmic ray events collected during the commissioning of the detector in 2008. The properties of the system are extensively tested and compared with the simulation. The effect of the random arrival time of the cosmic rays on the trigger performance is reported, and the results are compared with the design expectations for proton-proton collisions and with previous measurements obtained with muon beams.

  • 16. Chatrchyan, S.
    et al.
    Gonzalez Suarez, Rebeca
    Univ Cantabria, CSIC, IFCA, E-39005 Santander, Spain.
    White, A.
    Performance of the CMS hadron calorimeter with cosmic ray muons and LHC beam data2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5, article id T03012Article in journal (Refereed)
    Abstract [en]

    The CMS Hadron Calorimeter in the barrel, endcap and forward regions is fully commissioned. Cosmic ray data were taken with and without magnetic field at the surface hall and after installation in the experimental hall, hundred meters underground. Various measurements were also performed during the few days of beam in the LHC in September 2008. Calibration parameters were extracted, and the energy response of the HCAL determined from test beam data has been checked.

  • 17.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Charged particle multiplicities in $pp$ interactions at $\sqrts=0.9$, 2.36, and 7 TeV2011In: JHEP, Vol. 01Article in journal (Refereed)
    Abstract [en]

    Measurements of primary charged hadron multiplicity distributions are pre-sented for non-single-diffractive events in proton-proton collisions at centre-of-mass energiesof√s= 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from|η|<0.5 to|η|<2.4.The data were collected with the minimum-bias trigger of the CMS experiment during theLHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distributionat√s= 0.9 TeV is in agreement with previous measurements. At higher energies the in-crease of the mean multiplicity with√sis underestimated by most event generators. Theaverage transverse momentum as a function of the multiplicity is also presented. The mea-surement of higher-order moments of the multiplicity distribution confirms the violation ofKoba-Nielsen-Olesen scaling that has been observed at lower energies.

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  • 18.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    CMS Tracking Performance Results from early LHC Operation2010In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 70, p. 1165-1192Article in journal (Refereed)
    Abstract [en]

    The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.

  • 19.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Commissioning and Performance of the CMS Pixel Tracker with Cosmic Ray Muons2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The pixel detector of the Compact Muon Solenoid experiment consists of three barrel layers and two disks for each endcap. The detector was installed in summer 2008, commissioned with charge injections, and operated in the 3.8 T magnetic field during cosmic ray data taking. This paper reports on the first running experience and presents results on the pixel tracker performance, which are found to be in line with the design specifications of this detector. The transverse impact parameter resolution measured in a sample of high momentum muons is 18 microns.

  • 20.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Commissioning and Performance of the CMS Silicon Strip Tracker with Cosmic Ray Muons2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    During autumn 2008, the Silicon Strip Tracker was operated with the full CMS experiment in a comprehensive test, in the presence of the 3.8 T magnetic field produced by the CMS superconducting solenoid. Cosmic ray muons were detected in the muon chambers and used to trigger the readout of all CMS sub-detectors. About 15 million events with a muon in the tracker were collected. The efficiency of hit and track reconstruction were measured to be higher than 99% and consistent with expectations from Monte Carlo simulation. This article details the commissioning and performance of the Silicon Strip Tracker with cosmic ray muons.

  • 21.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Dijet Azimuthal Decorrelations in $pp$ Collisions at $\sqrts = 7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
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  • 22.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    First Measurement of Bose-Einstein Correlations in proton-proton Collisions at $\sqrts$ =0.9 and 2.36 TeV at the LHC2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105Article in journal (Refereed)
    Abstract [en]

    Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 and 2.36 TeV center-of-mass energies, recorded by the CMS experiment at the CERN Large Hadron Collider. The signal is observed in the form of an enhancement of pairs of same-sign charged particles with small relative four-momentum. The size of the correlated particle emission region is seen to increase significantly with the particle multiplicity of the event.

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  • 23.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    First Measurement of Hadronic Event Shapes in $pp$ Collisions at $\sqrt s=7$ TeV2011In: Phys. Lett., Vol. 699, no 1-2, p. 48-67Article in journal (Refereed)
    Abstract [en]

    Hadronic event shapes have been measured in proton–proton collisions at s=7TeV" role="presentation">s=7TeV" role="presentation">, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2pb&#x2212;1" role="presentation">. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.

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  • 24.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    First Measurement of the Cross Section for Top-Quark Pair Production in Proton-Proton Collisions at $\sqrts=7$ TeV2011In: Phys. Lett., Vol. B695, p. 424-443Article in journal (Refereed)
    Abstract [en]

    The first measurement of the cross section for top-quark pair production in pp collisions at theLarge Hadron Collider at center-of-mass energy√s=7 TeV has been performed using a data samplecorresponding to an integrated luminosity of 3.1±0.3pb−1recorded by the CMS detector. This resultutilizes the final state with two isolated, highly energetic charged leptons, large missing transverseenergy, and two or more jets. Backgrounds from Drell–Yan and non-W/Z boson production are estimatedfrom data. Eleven events are observed in the data with 2.1±1.0 events expected from background. Themeasured cross section is 194±72(stat.)±24(syst.)±21(lumi.)pb, consistent with next-to-leading orderpredicti

  • 25.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    First Measurement of the Underlying Event Activity at the LHC with $\sqrts = 0.9$ TeV2010In: The European Physical Journal Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 70, p. 555-572Article in journal (Refereed)
    Abstract [en]

    A measurement of the underlying activity in scattering processes with p T scale in the GeV region is performed in proton–proton collisions at s=0.9" role="presentation">s√=0.9 TeV, using data collected by the CMS experiment at the LHC. Charged particle production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged particles with pseudorapidity |η|<2, p T >0.5 GeV/c, and azimuthal direction transverse to that of the leading object.

  • 26.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Inclusive b-hadron production cross section with muons in $pp$ collisions at $\sqrts = 7$ TeV2011In: JHEP, Vol. 03Article in journal (Refereed)
  • 27.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of $B\barB$ Angular Correlations based on Secondary Vertex Reconstruction at $\sqrts=7$ TeV2011In: JHEP, Vol. 03Article in journal (Refereed)
    Abstract [en]

    A measurement of the angular correlations between beauty and anti-beauty hadrons (BB&#x00AF;" role="presentation">BB¯¯¯¯) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential BB&#x00AF;" role="presentation">BB¯¯¯¯ production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 pb−1, shows that a sizable fraction of the BB&#x00AF;" role="presentation">BB¯¯¯¯ pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of bb&#x00AF;" role="presentation">bb¯¯¯ production

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  • 28.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of Bose-Einstein Correlations in $pp$ Collisions at $\sqrts=0.9$ and 7 TeV2011In: JHEP, Vol. 05Article in journal (Refereed)
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  • 29.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of Dijet Angular Distributions and Search for Quark Compositeness in pp Collisions at $sqrts = 7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
    Abstract [en]

    Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at √s=7  TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36  pb−1. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Λ+=5.6  TeV (Λ−=6.7  TeV) for destructive (constructive) interference is obtained at the 95% confidence level.

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  • 30.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of the $B^+$ Production Cross Section in pp Collisions at $\sqrts = 7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
    Abstract [en]

    Measurements of the total and differential cross sections dσ/dpBT and dσ/dyB for B+ mesons produced in pp collisions at √s=7  TeV are presented. The data correspond to an integrated luminosity of 5.8  pb−1 collected by the CMS experiment operating at the LHC. The exclusive decay B+→J/ψK+, with J/ψ→μ+μ−, is used to detect B+ mesons and to measure the production cross section as a function of pBT and yB. The total cross section for pBT>5  GeV and |yB|<2.4 is measured to be 28.1±2.4±2.0±3.1  μb, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement.

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  • 31.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of the charge ratio of atmospheric muons with the CMS detector2010In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 692, p. 83-104Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766&#xB1;0.0032(stat.)&#xB1;0.0032(syst.)" role="presentation">, independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments.

  • 32.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of the Isolated Prompt Photon Production Cross Section in $pp$ Collisions at $\sqrts = 7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
    Abstract [en]

    The differential cross section for the inclusive production of isolated prompt photons has been measured as a function of the photon transverse energy EγT in pp collisions at √s=7  TeV using data recorded by the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.9  pb−1. Photons are required to have a pseudorapidity |ηγ|<1.45 and EγT>21  GeV, covering the kinematic region 0.006<xT<0.086. The measured cross section is found to be in agreement with next-to-leading-order perturbative QCD calculations

  • 33.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurement of the Muon Stopping Power in Lead Tungstate2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    A large sample of cosmic ray events collected by the CMS detector is exploited to measure the specific energy loss of muons in the lead tungstate (PbWO4) of the electromagnetic calorimeter. The measurement spans a momentum range from 5 GeV/c to 1 TeV/c. The results are consistent with the expectations over the entire range. The calorimeter energy scale, set with 120 GeV/c electrons, is validated down to the sub-GeV region using energy deposits, of order 100 MeV, associated with low-momentum muons. The muon critical energy in PbWO4 is measured to be 160+5−6±8 GeV, in agreement with expectations. This is the first experimental determination of muon critical energy.

  • 34.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Measurements of Inclusive $W$ and $Z$ Cross Sections in $pp$ Collisions at $\sqrts=7$ TeV2011In: JHEP, Vol. 01Article in journal (Refereed)
    Abstract [en]

    bstract

    Measurements of inclusive W and Z boson production cross sections in pp collisions at s=7" role="presentation">s√=7

    TeV are presented, based on 2.9 pb−1 of data recorded by the CMS detector at the LHC. The measurements, performed in the electron and muon decay channels, are combined to give &#x03C3;(pp&#x2192;WX)&#x00D7;B(W&#x2192;&#x2113;&#x03BD;)=9.95&#x00B1;0.07(stat.)&#x00B1;0.28(syst.)&#x00B1;1.09" role="presentation">σ(pp→WX)×B(W→ℓν)=9.95±0.07(stat.)±0.28(syst.)±1.09 (lumi.) nb and &#x03C3;(pp&#x2192;ZX)&#x00D7;B(Z&#x2192;&#x2113;+&#x2113;&#x2212;)=0.931&#x00B1;0.026(stat.)&#x00B1;0.023(syst.)&#x00B1;0.102" role="presentation">σ(pp→ZX)×B(Z→ℓ+ℓ−)=0.931±0.026(stat.)±0.023(syst.)±0.102 (lumi.) nb, where ℓ stands for either e or μ. Theoretical predictions, calculated at the next-to-next-to-leading order in QCD using recent parton distribution functions, are in agreement with the measured cross sections. Ratios of cross sections, which incur an experimental systematic uncertainty of less than 4%, are also reported.

  • 35.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Observation and studies of jet quenching in PbPb collisions at nucleon-nucleon center-of-mass energy = 2.76 TeV2011In: Phys. Rev., Vol. C84Article in journal (Refereed)
    Abstract [en]

    Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7μb−1. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet pT=120 GeV/c) up to the statistical limit of the available data sample (jet pT≈210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.

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  • 36.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Observation of Long-Range Near-Side Angular Correlations in Proton-Proton Collisions at the LHC2010In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 09, article id 91Article in journal (Refereed)
    Abstract [en]

    Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (η) and azimuthal angle (ϕ). Short-range correlations in Δη, which are studied in minimum bias events, are characterized using a simple “independent cluster” parametrization in order to quantify their strength (cluster size) and their extent in η (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb−1 data set at 7 TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p T of 1–3 GeV/c, 2.0 < |Δη| < 4.8 and Δϕ ≈ 0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in pp or pp&#x00AF;" role="presentation">pp¯¯¯ collisions.

  • 37.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance of CMS Muon Reconstruction in Cosmic-Ray Events2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The performance of muon reconstruction in CMS is evaluated using a large data sample of cosmic-ray muons recorded in 2008. Efficiencies of various high-level trigger, identification, and reconstruction algorithms have been measured for a broad range of muon momenta, and were found to be in good agreement with expectations from Monte Carlo simulation. The relative momentum resolution for muons crossing the barrel part of the detector is better than 1% at 10 GeV/c and is about 8% at 500 GeV/c, the latter being only a factor of two worse than expected with ideal alignment conditions. Muon charge misassignment ranges from less than 0.01% at 10 GeV/c to about 1% at 500 GeV/c.

  • 38.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance of the CMS Cathode Strip Chambers with Cosmic Rays2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47μm to 243μm. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns.

  • 39.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Performance of the CMS Level-1 Trigger during Commissioning with Cosmic Ray Muons2010In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 5Article in journal (Refereed)
    Abstract [en]

    The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-taking runs in 2008, and to estimate the level of detector noise. This paper describes the trigger components used, the algorithms that were executed, and the trigger synchronisation. Using data from extended cosmic ray runs, the muon, electron/photon, and jet triggers have been validated, and their performance evaluated. Efficiencies were found to be high, resolutions were found to be good, and rates as expected.

  • 40.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Prompt and non-prompt $J/ψ$ production in $pp$ collisions at $\sqrts=7$ TeV2011In: Eur. Phys. J., Vol. C71Article in journal (Refereed)
    Abstract [en]

    The production of J/ψ mesons is studied in pp collisions at s=7" role="presentation">s√=7 TeV with the CMS experiment at the LHC. The measurement is based on a dimuon sample corresponding to an integrated luminosity of 314 nb−1. The J/ψ differential cross section is determined, as a function of the J/ψ transverse momentum, in three rapidity ranges. A fit to the decay length distribution is used to separate the prompt from the non-prompt (b hadron to J/ψ) component. Integrated over J/ψ transverse momentum from 6.5 to 30 GeV/c and over rapidity in the range |y|<2.4, the measured cross sections, times the dimuon decay branching fraction, are 70.9±2.1(stat.)±3.0(syst.)±7.8(luminosity) nb for prompt J/ψ mesons assuming unpolarized production and 26.0±1.4(stat.)±1.6(syst.)±2.9(luminosity) nb for J/ψ mesons from b-hadron decays.

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  • 41.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for a Heavy Bottom-like Quark in $pp$ Collisions at $\sqrts = 7$ TeV2011In: Phys. Lett., Vol. 701, p. 204-223Article in journal (Refereed)
  • 42.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for a heavy gauge boson $W$ ’ in the final state with an electron and large missing transverse energy in $pp$ collisions at $\sqrts=7$ TeV2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. B698, p. 21-39Article in journal (Refereed)
    Abstract [en]

    A search for a heavy gauge boson W&#x2032;" role="presentation"> has been conducted by the CMS experiment at the LHC in the decay channel with an electron and large transverse energy imbalance ETmiss" role="presentation">, using proton–proton collision data corresponding to an integrated luminosity of 36pb&#x2212;1" role="presentation">. No excess above standard model expectations is seen in the transverse mass distribution of the electron-ETmiss" role="presentation"> system. Assuming standard-model-like couplings and decay branching fractions, a W&#x2032;" role="presentation"> boson with a mass less than 1.36TeV/c2" role="presentation"> is excluded at 95% confidence level.

  • 43.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for a $W^\prime$ boson decaying to a muon and a neutrino in $pp$ collisions at $\sqrts = 7$ TeV2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. B701, p. 160-179Article in journal (Refereed)
    Abstract [en]

    A new heavy gauge boson, W&#x2032;" role="presentation">, decaying to a muon and a neutrino, is searched for in pp collisions at a centre-of-mass energy of 7 TeV. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 36 pb−1. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the muon–neutrino system. Masses below 1.40 TeV are excluded at the 95% confidence level for a sequential standard-model-like W&#x2032;" role="presentation">. The W&#x2032;" role="presentation"> mass lower limit increases to 1.58 TeV when the present analysis is combined with the CMS result for the electron channel.

  • 44.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Dijet Resonances in 7 TeV pp Collisions at CMS2010In: Phys. Rev. Lett., Vol. 105Article in journal (Refereed)
  • 45.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for heavy Higgs bosons decaying into two tau leptons with the ATLAS detector using $pp$ collisions at $\sqrts=13$ TeV2020In: Article in journal (Refereed)
  • 46.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Heavy Stable Charged Particles in $pp$ collisions at $\sqrts=7$ TeV2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 03, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The result of a search at the LHC for heavy stable charged particles produced in pp collisions at s=7TeV" role="presentation">s√=7TeV is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 pb−1. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398GeV/c 2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c 2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

  • 47.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Microscopic Black Hole Signatures at the Large Hadron Collider2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 697, no 5, p. 434-453Article in journal (Refereed)
    Abstract [en]

    A search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb−1. Events with large total transverse energy are analyzed for the presence of multiple high-energy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities and model-independent limits on new physics in these final states are set. Using simple semi-classical approximation, limits on the minimum black hole mass are derived as well, in the range 3.5–4.5 TeV. These are the first direct limits on black hole production at a particle accelerator.

  • 48.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Pair Production of First-Generation Scalar Leptoquarks in $pp$ Collisions at $\sqrts=7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
    Abstract [en]

    A search for pair production of first-generation scalar leptoquarks is performed in the final state containing two electrons and two jets using proton-proton collision data at √s=7  TeV. The data sample used corresponds to an integrated luminosity of 33  pb−1 collected with the CMS detector at the CERN LHC. The number of observed events is in good agreement with the predictions for the standard model background processes, and an upper limit is set on the leptoquark pair production cross section times β2 as a function of the leptoquark mass, where β is the branching fraction of the leptoquark decay to an electron and a quark. A 95% confidence level lower limit is set on the mass of a first-generation scalar leptoquark at 384 GeV for β=1, which is the most stringent direct limit to date.

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  • 49.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Pair Production of Second-Generation Scalar Leptoquarks in $pp$ Collisions at $\sqrts=7$ TeV2011In: Phys. Rev. Lett., Vol. 106Article in journal (Refereed)
    Abstract [en]

    A search for pair production of second-generation scalar leptoquarks in the final state with two muons and two jets is performed using proton-proton collision data at √s=7  TeV collected by the CMS detector at the LHC. The data sample used corresponds to an integrated luminosity of 34  pb−1. The number of observed events is in good agreement with the predictions from the standard model processes. An upper limit is set on the second-generation leptoquark cross section times β2 as a function of the leptoquark mass, and leptoquarks with masses below 394 GeV are excluded at a 95% confidence level for β=1, where β is the leptoquark branching fraction into a muon and a quark. These limits are the most stringent to date.

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  • 50.
    Gonzalez Suarez, Rebeca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Search for Physics Beyond the Standard Model in Opposite-Sign Dilepton Events at $\sqrts = 7$ TeV2011In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 06Article in journal (Refereed)
    Abstract [en]

    A search is presented for physics beyond the standard model (SM) in final states with opposite-sign isolated lepton pairs accompanied by hadronic jets and missing transverse energy. The search is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 34 pb−1. No evidence for an event yield beyond SM expectations is found. An upper limit on the non-SM contribution to the signal region is deduced from the results. This limit is interpreted in the context of the constrained minimal supersymmetric model. Additional information is provided to allow testing the exclusion of specific models of physics beyond the SM.

12 1 - 50 of 61
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