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A search for leptoquarks with the ATLAS detector and hardware tracking at the High-Luminosity LHC
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics. (ATLAS)ORCID iD: 0000-0002-7288-3610
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a search for pair-production of scalar leptoquarks, decaying into third-generation particles, using proton-proton collisions delivered by the Large Hadron Collider (LHC) and recorded by the ATLAS detector. It also presents the development of a hardware track trigger for the Phase-II upgrade of the ATLAS experiment.

The search for pair-production of leptoquarks is performed using data collected by the ATLAS detector in 2015 and 2016 at a center-of-mass energy of 13 TeV. The total integrated luminosity of this data set amounts to 36.1 fb−1 . The search sensitivity is optimized for up-type leptoquarks where both leptoquarks decay to a b-quark and a τ -lepton. However, it also proves sensitive to down-type leptoquarks where both leptoquarks decay to a top-quark and a τ -lepton. The data is found to be compatible with the Standard Model, so exclusion limits are set on the leptoquark mass.

After the High Luminosity upgrade of the LHC, the ATLAS detector faces a 5–7 times increase in the number of simultaneous proton-proton collisions. To benefit from this increase in luminosity, the ATLAS detector has to maintain low trigger thresholds while keeping manageable trigger rates. A crucial part of the solution is the development of Hardware Tracking for the Trigger (HTT). The HTT first selects hit clusters in the inner tracking detector using associative memories and uses the selected clusters to perform linearized track-fits. This thesis presents the HTT system with focus on using the Hough transform as an alternative to associative memories to select clusters in the inner detector. The performance of the Hough transform is studied and a hardware implementation is discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 123
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1833
Keywords [en]
Leptoquarks, Hough transform, LHC, ATLAS, HL-LHC, Particle physics, Particle tracking, Cluster finding, Trigger
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-390352ISBN: 978-91-513-0707-7 (print)OAI: oai:DiVA.org:uu-390352DiVA, id: diva2:1341509
Public defence
2019-09-27, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-09-04 Created: 2019-08-08 Last updated: 2019-09-17
List of papers
1. Searches for third-generation scalar leptoquarks in √s = 13 TeV pp collisions with the ATLAS detector
Open this publication in new window or tab >>Searches for third-generation scalar leptoquarks in √s = 13 TeV pp collisions with the ATLAS detector
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2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 6, article id 144Article in journal (Refereed) Published
Abstract [en]

Limits are set on the pair production of scalar leptoquarks, where all possible decays of the leptoquark into a quark (t, b) and a lepton (, ) of the third generation are considered. The limits are presented as a function of the leptoquark mass and the branching ratio into charged leptons for up-type (LQ<sub ) and down-type (/t) leptoquarks. Many results are reinterpretations of previously published ATLAS searches. In all cases, LHC proton-proton collision data at a centre-of-mass energy of = 13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb(-1). Masses below 800 GeV are excluded for both LQu and LQd independently of the branching ratio, with masses below about 1 TeV being excluded for the limiting cases of branching ratios equal to zero or unity.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Hadron-Hadron scattering (experiments)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-390809 (URN)10.1007/JHEP06(2019)144 (DOI)000473621100001 ()
Note

For complete list of authors see http://dx.doi.org/10.1007/JHEP06(2019)144

Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-08-22Bibliographically approved
2. Fast pattern recognition with the ATLAS L1 track trigger for the HL-LHC
Open this publication in new window or tab >>Fast pattern recognition with the ATLAS L1 track trigger for the HL-LHC
2017 (English)In: PoS - Proceedings of Science, ISSN 1824-8039, E-ISSN 1824-8039, Vol. Vertex2016, p. 69-Article in journal (Refereed) Published
Abstract [en]

A fast hardware based track trigger is being developed in ATLAS for the High Luminosity upgrade of the Large Hadron Collider. The goal is to achieve trigger levels in the high pile-up conditions of the High Luminosity Large Hadron Collider that are similar or better than those achieved at low pile-up conditions by adding tracking information to the ATLAS hardware trigger. A method for fast pattern recognition using the Hough transform is investigated. In this method, detector hits are mapped onto a 2D parameter space with one parameter related to the transverse momentum and one to the initial track direction. The performance of the Hough transform is studied at different pile-up values. It is also compared, using full event simulation of events with average pile-up of 200, with a method based on matching detector hits to pattern banks of simulated tracks stored in a custom made Associative Memory ASICs. The pattern recognition is followed by a track fitting step which calculates the track parameters. The speed and precision of the track fitting depends on the quality of the hits selected by the pattern recognition step. The figures of merit of the pattern recognition are measured by the efficiency for finding hits from high transverse momentum tracks and the power of rejecting hits from low transverse momentum tracks and fake tracks.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-390268 (URN)10.22323/1.287.0069 (DOI)
Conference
C16-09-26
Available from: 2019-08-08 Created: 2019-08-08 Last updated: 2019-08-22Bibliographically approved
3. The design and simulated performance of a fast Level 1 track trigger for the ATLAS High Luminosity Upgrade
Open this publication in new window or tab >>The design and simulated performance of a fast Level 1 track trigger for the ATLAS High Luminosity Upgrade
2017 (English)In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 150, article id 00008Article in journal (Refereed) Published
Abstract [en]

The ATLAS experiment at the High Luminosity LHC will face a fivefold increase in the number of interactions per bunch crossing relative to the ongoing Run 2. This will require a proportional improvement in rejection power at the earliest levels of the detector trigger system, while preserving good signal efficiency. One critical aspect of this improvement will be the implementation of precise track reconstruction, through which sharper trigger turn-on curves can be achieved, and b-tagging and tau-tagging techniques can in principle be implemented. The challenge of such a project comes in the development of a fast, custom electronic device integrated in the hardware based first trigger level of the experiment. This article will discuss the requirements, architecture and projected performance of the system in terms of tracking, timing and physics, based on detailed simulations. Studies are carried out using data from the strip subsystem only or both strip and pixel subsystems.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-352946 (URN)10.1051/epjconf/201715000008 (DOI)000426612900008 ()
Conference
Workshop on Connecting The Dots / Workshop on Intelligent Trackers (CTD/WIT), MAR 06-09, 2017, Orsay, FRANCE
Available from: 2018-06-12 Created: 2018-06-12 Last updated: 2019-08-08Bibliographically approved
4. Comparison of two hardware-based hit filtering methods for trackers in high-pileup environments
Open this publication in new window or tab >>Comparison of two hardware-based hit filtering methods for trackers in high-pileup environments
2018 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 13, article id P04019Article in journal (Refereed) Published
Abstract [en]

As experiments in high energy physics aim to measure increasingly rare processes, the experiments continually strive to increase the expected signal yields. In the case of the High Luminosity upgrade of the LHC, the luminosity is raised by increasing the number of simultaneous proton-proton interactions, so-called pileup. This increases the expected yields of signal and background processes alike. The signal is embedded in a large background of processes that mimic that of signal events. It is therefore imperative for the experiments to develop new triggering methods to effectively distinguish the interesting events from the background.& para;& para;We present a comparison of two methods for filtering detector hits to be used for triggering on particle tracks: one based on a pattern matching technique using Associative Memory (AM) chips and the other based on the Hough transform. Their efficiency and hit rejection are evaluated for proton-proton collisions with varying amounts of pileup using a simulation of a generic silicon tracking detector. It is found that, while both methods are feasible options for a track trigger with single muon efficiencies around 98-99%, the AM based pattern matching produces a lower number of hit combinations with respect to the Hough transform whilst keeping more of the true signal hits. We also present the effect on the two methods of increasing the amount of support material in the detector and of introducing inefficiencies by deactivating detector modules. The increased support material has negligable effects on the efficiency for both methods, while dropping 5% (10%) of the available modules decreases the efficiency to about 95% (87%) for both methods, irrespective of the amount of pileup.

Keywords
Data reduction methods, Online farms and online filtering, Trigger algorithms, Particle tracking detectors
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-353216 (URN)10.1088/1748-0221/13/04/P04019 (DOI)000430374800001 ()
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2019-08-08Bibliographically approved
5. To catch a long-lived particle: hit selection towards a regional hardware track trigger implementation
Open this publication in new window or tab >>To catch a long-lived particle: hit selection towards a regional hardware track trigger implementation
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2019 (English)In: Article in journal (Refereed) Submitted
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-389892 (URN)
Available from: 2019-07-31 Created: 2019-07-31 Last updated: 2019-08-08

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