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Silicon Tracking and a Search for Long-lived Particles
Stockholm University, Faculty of Science, Department of Physics. Lawrence Berkeley National Lab.ORCID iD: 000-0001-5659-4440
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The ATLAS Detector, below the surface of the Swiss-French border, measures the remnants of high-energy proton-proton collisions, accelerated by the Large Hadron Collider (LHC) at CERN. Recently the LHC paused operations, having delivered an integrated luminosity corresponding to 150 fb−1 of data at a centre-of-mass energy of 13 TeV. This thesis describes a search for physics beyond the Standard Model using that dataset as well as the charged particle tracking detector technology that renders it possible. The analysis searches for long-lived, massive particles identified by a characteristic decay displaced from the interaction point and produced in association with high momentum jets.

Searching for rare processes requires sifting through a large amount of data, which stresses the ATLAS computing infrastructure. As such, measures are taken to reduce unnecessary computations and supplement our existing resources with, for example, inherently parallel computing architectures. Early adoption of these new architectures is necessary to understand the feasibility of their potential integration, including porting existing algorithms. A popular algorithm used in track reconstruction, the Kalman filter, has been implemented in a neuromorphic architecture: IBM’s TrueNorth. The limits of using such an architecture for tracking, as well as how its performance compares to a non-spiking Kalman filter implementation, are explored in this thesis.

In 2026 the LHC will enter a High Luminosity phase (HL-LHC), increasing the instantaneous luminosity by a factor of five and delivering 4000 fb-1 within twelve years. This will impose significant technical challenges on all aspects of the ATLAS detector, resulting in the entire ATLAS Inner Detector being replaced by an all-silicon tracker. ITk (the new “Inner TracKer”) will be comprised of Strip and Pixel detectors. The layout of the Pixel and Strip detectors was optimised for the upgrade to extend their forward coverage. To cope with the increased number of hits per chip per event and explore novel techniques for dealing with the conditions in HL-LHC, an inter-experiment collaboration, RD53, was formed, tasked with producing a front-end readout chip used in Pixel detectors. This thesis will briefly outline the author’s contribution to both of these projects.

ITk silicon sensors will undergo significant damage over their lifetime due to non-ionising energy loss (NIEL). This damage must be incorporated into the detector simulation both to predict the detector performance and to understand the effects of radiation damage on data taking. The implementation of NIEL radiation damage in the ATLAS simulation framework is discussed in this thesis.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019. , p. 208
Keywords [en]
ATLAS, silicon, silicon tracking, radiation damage, neuromorphic, neuromorphic computing, long-lived particles, susy, rpvll, displaced vertices, pixel, pixel detector
National Category
Subatomic Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-168230ISBN: 978-91-7797-733-9 (print)ISBN: 978-91-7797-734-6 (electronic)OAI: oai:DiVA.org:su-168230DiVA, id: diva2:1307158
Public defence
2019-06-13, sal FB42 AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

 

Available from: 2019-05-21 Created: 2019-04-26 Last updated: 2019-11-01Bibliographically approved
List of papers
1. Performance of silicon pixel detectors at small track incidence angles for the ATLAS Inner Tracker Upgrade
Open this publication in new window or tab >>Performance of silicon pixel detectors at small track incidence angles for the ATLAS Inner Tracker Upgrade
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2016 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 831, p. 254-259Article in journal (Refereed) Published
Abstract [en]

In order to enable the ATLAS experiment to successfully track charged particles produced in high-energy collisions at the High-Luminosity Large Hadron Collider, the current ATLAS Inner Detector will be replaced by the Inner Tracker (ITk), entirely composed of silicon pixel and strip detectors. An extension of the tracking coverage of the ITk to very forward pseudorapidity values is proposed, using pixel modules placed in a long cylindrical layer around the beam pipe. The measurement of long pixel clusters, detected when charged particles cross the silicon sensor at small incidence angles, has potential to significantly improve the tracking efficiency, fake track rejection, and resolution of the ITk in the very forward region. The performance of state-of-the-art pixel modules at small track incidence angles is studied using test beam data collected at SLAC and CERN.

Keywords
LHC, High Luminosity, ATLAS upgrade, Inner Tracker, Pixel detector, Forward tracking
National Category
Subatomic Physics Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-168224 (URN)10.1016/j.nima.2016.03.099 (DOI)
Conference
10th International 'Hiroshima' Symposium on the Development and Application of Semiconductor Tracking Detectors (HSTD-10), Xian, China, 25-29 September, 2015
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-04-26Bibliographically approved
2. Results of FE65-P2 Pixel Readout Test Chip for High Luminosity LHC Upgrades
Open this publication in new window or tab >>Results of FE65-P2 Pixel Readout Test Chip for High Luminosity LHC Upgrades
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2017 (English)In: PoS - Proceedings of Science, ISSN 1824-8039, E-ISSN 1824-8039, Vol. 282Article in journal (Refereed) Published
Abstract [en]

A pixel readout test chip called FE65-P2 has been fabricated on 65 nm CMOS technology. FE65-P2 contains a matrix of 64 x 64 pixels on 50 micron by 50 micron pitch, designed to read out a bump bonded sensor. The goals of FE65-P2 are to demonstrate excellent analog performance isolated from digital activity well enough to achieve 500 electron stable threshold, be radiation hard to at least 500 Mrad, and prove the novel concept of isolated analog front ends embedded in a flat digital design, dubbed “analog islands in a digital sea”. Experience from FE65-P2 and hybrid assemblies will be applied to the design for a large format readout chip, called RD53A, to be produced in a wafer run in early 2017 by the RD53 collaboration. We review the case for 65 nm technology and report on threshold stability test results for the FE65-P2.

National Category
Subatomic Physics Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-168225 (URN)10.22323/1.282.0272 (DOI)
Conference
38th International Conference on High Energy PhysicsChicago, USA, 3-10 August, 2016
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-04-26Bibliographically approved
3. Modelling radiation damage to pixel sensors in the ATLAS detector
Open this publication in new window or tab >>Modelling radiation damage to pixel sensors in the ATLAS detector
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2019 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, article id P06012Article in journal (Refereed) Published
Abstract [en]

Silicon pixel detectors are at the core of the current and planned upgrade of the ATLAS experiment at the LHC. Given their close proximity to the interaction point, these detectors will be exposed to an unprecedented amount of radiation over their lifetime. The current pixel detector will receive damage from non-ionizing radiation in excess of 10(15) 1 MeV n(eq)/cm(2), while the pixel detector designed for the high-luminosity LHC must cope with an order of magnitude larger fluence. This paper presents a digitization model incorporating effects of radiation damage to the pixel sensors. The model is described in detail and predictions for the charge collection efficiency and Lorentz angle are compared with collision data collected between 2015 and 2017 (<= 10(15) 1 MeV n(eq)/cm(2)).

Keywords
Detector modelling and simulations II (electric fields, charge transport, multiplication and induction, pulse formation, electron emission, etc), Radiation-hard detectors, Solid state detectors
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-171138 (URN)10.1088/1748-0221/14/06/P06012 (DOI)000472134700001 ()
Available from: 2019-09-16 Created: 2019-09-16 Last updated: 2019-11-01Bibliographically approved
4. Neuromorphic Kalman filter implementation in IBM's TrueNorth
Open this publication in new window or tab >>Neuromorphic Kalman filter implementation in IBM's TrueNorth
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2017 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 898, no 4, article id 042021Article in journal (Refereed) Published
Abstract [en]

Following the advent of a post-Moore’s law field of computation, novel architectures continue to emerge. With composite, multi-million connection neuromorphic chips like IBM’s TrueNorth, neural engineering has now become a feasible technology in this novel computing paradigm. High Energy Physics experiments are continuously exploring new methods of computation and data handling, including neuromorphic, to support the growing challenges of the field and be prepared for future commodity computing trends. This work details the first instance of a Kalman filter implementation in IBM’s neuromorphic architecture, TrueNorth, for both parallel and serial spike trains. The implementation is tested on multiple simulated systems and its performance is evaluated with respect to an equivalent non-spiking Kalman filter. The limits of the implementation are explored whilst varying the size of weight and threshold registers, the number of spikes used to encode a state, size of neuron block for spatial encoding, and neuron potential reset schemes.

National Category
Accelerator Physics and Instrumentation Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-168226 (URN)10.1088/1742-6596/898/4/042021 (DOI)
Conference
22nd International Conference on Computing in High Energy and Nuclear Physics, CHEP, San Francisco, USA, October 10-14, 2016
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-05-03Bibliographically approved

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