PhD Thesis Chapter 0

The Design of the ZEUS Regional First-Level Trigger Box and Associated Trigger Studies

Timothy Lawrence Short
Department of Physics and Astronomy
University of Bristol

A thesis submitted for the degree of Doctor of Philosophy

March 1992


The design of electronics suitable for fast event selection in the first level of the ZEUS trigger has been studied using a Monte Carlo simulation technique. It was found that integrating tracking information from two detectors (the Central Tracking Detector and the Forward Tracking Detector) at this level was both possible and beneficial. It was shown that this method improved efficiency of acceptance of DIS events of interest while enhancing rejection of background. The performance of this part of the trigger was investigated for other physics: heavy quark pair production and J/ψ events produced via boson-gluon fusion. A method of investigating the kinematic dependency of the Central Tracking Detector first level trigger in such a way as to reduce computer resources required to acceptable levels was devised and implemented.

“I want you to be able to tell your noble friends that Zeus has given us too a certain measure of success, which has held good from our forefathers’ time to the present day. Though our boxing and wrestling are not beyond criticism, we can run fast…”

Homer: The Odyssey, Book VIII.


I would like to acknowledge everyone in the Bristol Particle Physics Group: Adrian Cassidy, Dave Cussans, Tony Duell, Neil Dyce, Helen Fawcett, Robin Gilmore, Teresa Gornall, Tim Llewellyn, John Malos, Alex Martin, Jean-Pierre Melot, Carlos Morgado, Tony Sephton, Vince Smith, Bob Tapper, Simon Wilson and Kostas Xiloparkiotis.

At Oxford, Jonathan Butterworth, Doug Gingrich and especially Fergus Wilson have all helped at various times. I am indebted to Mark Lancaster for the diagram which appears on page 56 and to Alex Mass of the University of Bonn for the one on page 65. I would also like to thank Frank Chlebana of the University of Toronto. In particular my supervisor Brian Foster and Greg Heath have played a great part in this work.

During this work, I have been funded by the Science and Engineering Research Council.

I declare that no part of this thesis has been previously presented to this or any other university as part of the requirements of a higher degree.

The design of the ZEUS trigger, of which this work forms a part, has been the responsibility of many ZEUS collaboration members. At Bristol, I have been responsible for maintaining the trigger simulation software and underlying physics generator packages. I have been solely responsible for using this code to produce the results presented here except for those in chapter eight, which were obtained in collaboration with other ZEUSUK members.

Timothy Lawrence Short


1 Physics at HERA 1
1.1 The Standard Model
1.1.1 QED
1.1.2 Weak Interactions
1.1.3 Electro-weak unification
1.1.4 QCD
1.2 Types of events at HERA
1.2.1 Introduction
1.2.2 Deep Inelastic Scattering Events Introduction General Kinematics Jacquet-Blondel Kinematics Structure Functions and Scaling
1.2.3 Boson-gluon Fusion Heavy-Flavor Pair Production J/ψ Production
1.2.4 Exotica Excited Electrons Leptoquarks and Leptogluons Supersymmetry

2 Non-Tracking Elements of the ZEUS Detector
2.1 Introduction
2.2 Calorimetry
2.2.1 Introduction
2.2.2 Forward, Rear, Barrel Calorimeter (F/R/BCAL)
2.2.3 Backing Calorimeter (BAC)
2.2.4 Hadron Electron Separator
2.3 Muon Detectors
2.3.1 The Forward Muon Detector (FMUON)
2.3.2 Barrel/Rear Muon Detectors (B/RMUO)
2.4 Other Elements
2.4.1 The Veto-wall (VETO)
2.4.2 The Luminosity Monitor
2.4.3 Leading Proton Spectrometer (LPS)
2.4.4 Rucksack
2.4.5 Solenoid

3 Tracking Elements of the ZEUS Detector
3.1 Introduction
3.2 The Central Tracking Detector (CTD)
3.2.1 Introduction
3.2.2 Mechanical Construction
3.2.3 Electronic Readout R-φ coordinates Z-coordinate
3.3 Forward Detector (FDET)
3.3.1 The Forward Tracking Detector (FTD)
3.3.2 The Transition Radiation Detector (TRD)
3.4 The Rear Tracking Detector (RTD)
3.5 The Vertex Detector (VXD)

4 The ZEUS Trigger Environment
4.1 Introduction
4.1.1 Overview of Data-flow
4.2 Rates and Background
4.3 The Trigger
4.3.1 The First Level Trigger Calorimeter FLT Fast Clear Other FLT Components Global First Level Trigger Box
4.3.2 The Second Level Trigger Tracking Detector SLT Calorimeter SLT Other SLT Components
4.3.3 The Third Level Trigger

5 Tracking Detector FLT
5.1 Introduction
5.2.1 Cell Processors
5.2.2 Sector Processors
5.2.3 Processing
5.2.4 Timing
5.3.1 Introduction
5.3.2 Diamonds
5.3.3 Hardware

6 The Regional First Level Trigger Box
6.1 Introduction
6.1.1 Requirements
6.1.2 Information Available to the RBOX
6.1.3 Processing
6.2 Simulation
6.2.1 Geant and ZEUSGeant
6.2.2 ZGANA
6.2.3 Event Generation
6.3 Details of the Algorithm
6.3.1 Introduction
6.3.2 Standalone FTD Sub-trigger
6.3.3 Standalone CTD Sub-trigger
6.3.4 Barrel Combined Sub-trigger
6.3.5 Forward Combined Sub-trigger
6.4 Results
6.4.1 Sub-trigger Ratios
6.4.2 Tracking Triggers
6.4.3 Beam-gas Background Comparison of Different Generators Reasons for Beam-gas Leakage
6.4.4 Calorimetry
6.5 Hardware Design of the RBOX

7 Investigation of Kinematic Dependence of CTDFLT Efficiency
7.1 Introduction
7.1.1 Special Jacquet-Blondel Kinematics
7.2 Event Generation
7.3 Results
7.4 Discussion
7.5 Conclusions

8 Heavy-Flavor Events in the Regional First Level Trigger
8.1 Introduction
8.2 Simulation
8.3 Results
8.4 Discussion
8.5 Conclusions

9 Investigation of J/ψ Event Acceptance in the FLT
9.1 Introduction
9.2 Event Generation
9.3 Results
9.3.1 Trigger Efficiencies
9.3.2 Comparison of Signal and Background
9.4 Discussion
9.5 Conclusions

10 Conclusions


List of Figures

1.1 Feynman diagrams for electron-positron scattering in QED
1.2 Feynman diagram for DIS
1.3 The two lowest order QCD diagrams for BGF
1.4 Lowest order diagram for inelastic J/ψ production
2.1 Section through the ZEUS detector along the beam-line
2.2 Arrangement of cells in the calorimeter
2.3 The LPS stations along the straight section of the beam-line
3.1 Central Tracking Detector Coordinate Systems
3.3 Sketch of an FTD sub-chamber
4.1 Flow of data through the DAQ system
4.2 Trigger regions in the calorimeter
4.3 Forward muon detector first level trigger
4.4 Barrel muon detector first level trigger
4.5 LPS input to FLT: proton search
4.6 Schematic of logic in the GFLTB
5.1 Principle of the CTDFLT
5.2 One of the 32 trigger sectors of the CTDFLT
5.3 CTDFLT event classification flowchart
5.4 Crossing mis-identification
5.5 Method of diamond forming
5.6 Principle of the FTDFLT
5.7 Outline of two-crate FTDFLT hardware design
6.1 Mapping of the FTD onto CTD
6.2 Typical values of x for physics sample
6.3 Typical values of Q2 for physics sample
6.4 Sub-trigger ratios for beam-gas sample (zero bin removed)
6.5 Sub-trigger ratios for CC sample (zero bin removed)
6.6 Sub-trigger ratios for beam-gas sample
6.7 Sub-trigger ratios for CC sample
6.8 Profile of efficiency vs. leakage for CC events
6.9 Profile of efficiency vs. leakage for NC events
6.10 Cross-correlation plots for CC events
6.11 Cross-correlation plots for NC events
6.12 Beam-gas leakage vertex profile along the beam-line
6.13 Number of track vertices per event
6.14 Hit multiplicity distributions by event class
6.15 Transverse and longitudinal momenta of tracks by event class for beam-gas
6.16 Beamgas leakage vertex profile after ET cuts
6.17 Regional box functional subdivision
6.18 Regional box hardware scheme
6.19 Subdivision in θ of RBOX bitmap to GFLTB
7.1 Contours of fixed y in the x-θjet plane
7.2 Contours of fixed y in the Q2-θjet plane
7.3 Low statistics full angle pass for CC events
7.4 Low statistics full angle pass for NC events
7.5 Efficiency for CC events
8.1 Effect of multiplicity and transverse energy on acceptance
8.2 Multiplicity of charged tracks per event with a pt > 0.5 GeV/c for heavy flavor events
8.3 Total transverse energy (GeV) per event as measured by the calorimeter for heavy flavor events
8.4 Total transverse energy (GeV) per event as measured by the calorimeter for beam-gas events
8.5 Multiplicity of charged tracks per event with a pt > 0.5 GeV/c for beam-gas events
8.6 Polar angle of Geant tracks for HFLGEN and HERWIG events
9.1 Sum of visible transverse energy in the electromagnetic calorimeter
9.2 Sum of total transverse momentum (x-direction only)
9.3 Sum of total transverse visible energy
9.4 Veto-wall hits
9.5 Number of hits in C5 collimator for J/ψ events
9.6 Number of hits in C5 collimator for beam-gas events
9.7 Sub-trigger decision flowchart

List of Tables

1.1 Quark doublets
1.2 Lepton doublets
2.1 Polar angle coverage of calorimeter sections
2.2 Calorimeter readout tower size
4.1 Rates of physics and background
4.2 Processing time allowed per event by level of trigger
4.3 Calorimeter tower numbers and makeup by location
4.4 Total HAC and EMC energy deposited by a MIP by location of tower
4.5 FMUFLT polar angle subdivision
5.1 Summary of CTDFLT event classifications
6.1 Geant physics processes
6.2 Kinematic variables of CC sample
6.3 Proportion of beam-gas events in zero bin with non-zero denominator for the four sub-triggers
6.4 RBOX FLT cut values for the four sub-triggers
6.5 Results for CC events
6.6 Results for NC events
6.7 Results for beam-gas events
6.8 Event classifications for different generators
6.9 Transverse energy cuts chosen for the CTD
6.10 Transverse energy cuts chosen for the RBOX
7.1 CTDFLT efficiencies in the kinematic bins for θ-jet = 63° +/- 1°
7.2 CTDFLT efficiencies in the kinematic bins for θ-jet = 43° +/- 1°
7.3 CTDFLT efficiencies in the kinematic bins for θ-jet = 33° +/- 1°
7.4 CTDFLT efficiencies in the kinematic bins for θ-jet = 23° +/- 1°
7.5 CTDFLT efficiencies in the kinematic bins for θ-jet = 13° +/- 1°
7.6 Final combined figures for CTDFLT efficiency
8.1 Percentage of events accepted by the simple parametrization of the tracking and calorimeter first level trigger
8.2 FLT classifications for the full FLT simulations for ccbar events
8.3 FLT classifications for the full FLT simulations for bbbar events
9.1 Event classifications from ZGANA
9.2 Event classifications for the dedicated sub-trigger


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