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Upgrade of the Global Muon Trigger for the Compact Muon Solenoid Experiment at CERN”

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Upgrade of the Global Muon Trigger for the Compact Muon Solenoid Experiment at CERN” DISSERTATION/DOCTORAL THESIS Titel der Dissertation/Title of the Doctoral Thesis “Upgrade of the Global Muon Trigger for the Compact Muon Solenoid experiment at CERN” verfasst von/submitted by Mag. Dinyar Sebastian Rabady angestrebter akademischer Grad/in partial fulfilment of the requirements for the degree of Doktor der Naturwissenschaften (Dr. rer. nat.) Wien, im Jänner 2018/Vienna, in January 2018 Studienkennzahl lt. Studienblatt/ A 796 605 411 degree programme code as it appears on the student record sheet: Studienrichtung lt. Studienblatt/ Physik field of study as it appears onthe student record sheet: Betreut von/Supervisor: Dipl.-Ing. Dr. Claudia-Elisabeth Wulz Hon.-Prof. Dipl.-Phys. Dr. Eberhard Widmann Für meinen Großvater. Abstract The Large Hadron Collider is a large particle accelerator at the CERN research labo- ratory, designed to provide particle physics experiments with collisions at unprece- dented centre-of-mass energies. For its second running period both the number of colliding particles and their collision energy were increased. To cope with these more challenging conditions and maintain the excellent performance seen during the first running period, the Level-1 trigger of the Compact Muon Solenoid experiment — a so- phisticated electronics system designed to filter events in real-time — was upgraded. This upgrade consisted of the complete replacement of the trigger electronics andafull redesign of the system’s architecture. While the calorimeter trigger path now follows a time-multiplexed processing model where the entire trigger data for a collision are received by a single processing board, the muon trigger path was split into regional track finding systems where each newly introduced track finder receives data from all three muon subdetectors for a certain geometric detector slice and reconstructs fully formed muon tracks from this. In contrast, the system in operation during the first data taking period was built around subdetector-specific track finders whoseout- put tracks were merged in the Global Muon Trigger. This restructuring of the muon trigger required a novel system to receive muon objects from the track finding layer, remove any duplicate tracks, and forward the best-reconstructed objects to the global decision layer. The upgraded Global Muon Trigger (μGMT) was designed to satisfy the require- ments for such a system. It receives muon track data from all regional track finder processors as well as energy information from the final stage of the calorimeter trigger. These muon tracks are ranked and sorted, while in parallel their azimuthal coordinate is corrected and duplicate muon tracks are removed. An isolation variable using the calorimetric information is computed before the eight highest-ranked muon tracks are sent to the upgraded Global Trigger (μGT). The μGT then determines whether a read- out process shall be initiated by applying complex algorithms on the muon tracks as well as on data received from the calorimeter trigger chain. This thesis presents the design and development ofthe μGMT, outlining the re- quirements as well as challenges encountered during development of the upgraded trigger. Furthermore, the excellent performance of the new system is demonstrated in the context of studies on quarkonia: Both the impact of the improved duplicate removal system as well as of the correction of the azimuthal coordinate are evaluated and shown to improve upon the performance demonstrated by the original Level-1 trigger. Additionally, a simple scheme that increases the purity of dedicated trigger algorithms to select J/ψ mesons by requiring the presence of two oppositely charged muons is presented and assessed. i Kurzfassung Der Large Hadron Collider — ein großer Teilchenbeschleuniger am Forschungszen- trum CERN — wurde entworfen um Teilchenkollisionen mit beispiellosen Schwer- punktsenergien für Teilchenphysik-Experimente bereit zu stellen. Für dessen zwei- te Betriebsperiode wurden sowohl die Anzahl der kollidierenden Teilchen, als auch deren Kollisionsenergie erhöht. Um unter diesen herausfordernderen Bedingungen die hervorragende Leistung aufrechtzuerhalten die der Level-1 Trigger des Compact Muon Solenoid Detektors — ein komplexes Elektroniksystem das in Echtzeit Kolli- sionsereignisse filtert — während der ersten Betriebsperiode gezeigt hat, wareine Erweiterung seiner Funktionalität notwendig. Für diesen Ausbau wurde die gesam- te Trigger-Elektronik ersetzt und die Systemarchitektur überarbeitet. Während nun im Kalorimeter-Trigger die vollständige Trigger-Information für eine Kollision in ei- nem Prozessor verfügbar ist, wurde der Myonen-Trigger in regionale Spurenfinder- Systeme geteilt, bei denen jedes System Daten von allen drei Myonen-Subdetektoren für eine gewisse geometrische Region erhält und hieraus Spuren erstellt. Demgegen- über wurde im Trigger-System der ersten Betriebsperiode für jeden Subdetektor ein eigener Spurenfinder verwendet. Die Ergebnisse dieser Systeme wurden anschließend im Global Muon Trigger System vereinigt. Die Neugestaltung des Myonen-Triggers machte ein neuartiges System notwendig, welches die Resultate der neuen Spurenfin- der erhält, Duplikate entfernt und die am besten rekonstruierten Spuren an das globale Entscheidungssystem weiterleitet. Das neue Global Muon Trigger (μGMT) System wurde entworfen um die obigen Anforderungen zu erfüllen. Es erhält Myonen-Daten von allen regionalen Spurenfin- dern, wie auch Energie-Information von der finalen Stufe des Kalorimeter-Triggers. Die Myonen-Spuren werden gereiht und sortiert, während zeitgleich deren azimutale Koordinate korrigiert und Duplikate entfernt werden. Mit Hilfe der Kalorimeter-Infor- mationen wird eine Isolationsvariable berechnet, bevor die acht höchst-gereihten Spu- ren an das neue Global Trigger (μGT) System geschickt werden. Der μGT entscheidet mit Hilfe komplexer Algorithmen die auf die erhaltenen Objekte angewendet werden, ob ein Auslesevorgang des Detektors initiiert werden soll. Die vorliegende Arbeit präsentiert den μGMT. Es werden zunächst Anforderun- gen definiert und Herausforderungen während der Entwicklung besprochen, bevor das Design des μGMT präsentiert wird. Weiters wird die hervorragende Leistung des neuen Systems im Kontext von Quarkonia-Analysen gezeigt. Sowohl der Einfluss des verbesserten Duplikatentferungssystems als auch der Korrektur der azimutalen Ko- ordinate werden besprochen und deren positiver Effekt gezeigt. Außerdem wird ein Schema vorgestellt, welches die Reinheit eines dedizierten Trigger-Algorithmus um J/ψ-Mesonen zu selektieren erhöht indem zwei Myonen mit gegensätzlicher Ladung gesucht werden. iii Contents Abstract i Kurzfassung iii 1 Introduction 1 1.1 Overview of the thesis ............................... 1 1.2 Personal contributions ............................... 2 2 Quarkonium physics 3 2.1 Introduction ..................................... 3 2.2 Quarkonium production .............................. 4 2.3 Quarkonium polarisation .............................. 5 2.4 Challenges in the trigger system .......................... 7 3 The Large Hadron Collider 9 3.1 Introduction ..................................... 9 3.2 The injection chain ................................. 11 3.3 Luminosity ...................................... 11 3.4 Operational periods of the LHC .......................... 13 3.5 Experiments at the LHC ............................... 15 3.5.1 ALICE .................................... 15 3.5.2 ATLAS .................................... 16 3.5.3 CMS ..................................... 17 3.5.4 LHCb .................................... 18 4 The Compact Muon Solenoid experiment 21 4.1 Overview ....................................... 21 4.1.1 Geometry .................................. 21 4.1.2 Coordinate system ............................. 22 4.2 Inner tracking .................................... 23 4.2.1 The pixel detector .............................. 24 4.2.2 The silicon strip tracker .......................... 25 4.3 Calorimetry ..................................... 26 4.3.1 Electromagnetic calorimeter ........................ 26 4.3.2 Hadron calorimeter ............................. 27 v Contents 4.4 Forward detectors .................................. 28 4.4.1 Castor .................................... 28 4.4.2 Zero degree calorimeters .......................... 29 4.5 The superconducting solenoid ........................... 29 4.6 The muon system .................................. 31 4.6.1 Drift Tubes ................................. 32 4.6.2 Cathode Strip Chambers .......................... 33 4.6.3 Resistive Plate Chambers ......................... 35 4.7 Trigger and data acquisition ............................ 36 4.7.1 Upgrade of the DAQ and HLT during long shutdown 1 . 39 5 The Level-1 Trigger 41 5.1 Introduction ..................................... 41 5.2 The Level-1 trigger for LHC Run-1 ......................... 42 5.2.1 The calorimeter trigger ........................... 42 5.2.2 The muon trigger .............................. 46 5.2.3 The Global Trigger ............................. 53 5.2.4 The Timing, Trigger, and Control system . 54 5.3 The upgraded Level-1 trigger ............................ 54 5.3.1 Level-1 trigger hardware .......................... 56 5.3.2 The calorimeter trigger ........................... 57 5.3.3 The muon trigger .............................. 60 5.3.4 The upgraded Global Trigger ....................... 66 5.3.5 The Trigger Control and Distribution System . 66 5.4 Online control
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