[.Mis-mi —12792 NL91C0017 The ZEUS Second Level Calorimeter Trigger: Physics Simulation, Design and Implementation Sijbrand de Jong The ZEUS Second Level Calorimeter Trigger: Physics Simulation, Design and Implementation ACADEMISCH PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof. Dr. S. K. Thoden van Velzen ir het openbaar te verdedigen in de Aula der Universiteit (Oude Lutherse Kerk, ingang Singel 411, hoek Spui) op vrijdag 29 juni 1990 te 13.00 uur door Sijbrand Jan de Jong geboren te Amsterdam Promotor: Prof. Dr. J. J. Engelen The work described in this thesis is part of the research programme of 'het Nation- aal Instituut voor Kernfysica en Hoge-Energie Fysica (NIKHEF-H)' in Amster- dam. The author was financially supported by 'de Stichting voor Fundamental Onderzoek der Materie (FOM)'. Voor Ellen Contents 1 Introduction 1 2 Physics at HERA 5 2.1 The HERA collider 5 2.2 Physics at HERA 6 2.2.1 Notation convention 6 2.2.2 HERA kinematics 8 2.2.3 The proton structure 10 2.2.4 Tests of the standard model 16 2.2.5 Physics beyond the standard model 21 2.2.6 Backgrounds at HERA 22 3 ZEUS 27 3.1 ZEUS a detector for HERA 27 3.1.1 Tracking: momentum measurement and identifica- tion of charged particles 30 3.1.2 Energy measurement and identification of neutral and charged particles by calorimotry 34 3.1.3 The small angle detectors 36 3.2 Event signatures in ZEUS 36 3.2.1 Deep inelastic events 36 3.2.2 Heavy flavour events 37 3.2.3 Beam gas background events 37 3.3 More on the high resolution calorimeter 38 3.3.1 The FCAL and RCAL 40 3.3 2 The BCAL 42 3.4 The data acquisition and triggering system 43 3.4.1 The calorimeter readout 45 3.5 The calorimeter trigger processors 49 3.5.1 The first level calorimeter trigger processor 49 3.5.2 The fast clear processor 50 3.5.3 The second level calorimeter processor 51 4 The second level calorimeter trigger processor 53 4.1 The information available to the second level calorimeter trigger 53 4.2 The global sums 54 4.3 The cluster search 55 4.3.1 Hadronjets 56 4.3.2 Electron showers 59 4.3.3 Muons passing through the calorimeter 60 4.3.4 The clustering model 60 4.4 Hardware implementation 61 4.4.1 The NIKHEF two transputer VME module 61 4.4.2 The second level trigger network 67 4.4.3 The trigger processor network 70 4.5 Software implementation 74 4.5.1 The coordinate systems 74 4.5.2 Layer 1: Building the pre-clusters 76 4.5.3 Layer 2: Combining the pre-clusters for the FCAL, BCAL and RCAL 78 4.5.4 Layer 3: Combining the pre-clusters from FCAL, BCAL and RCAL 78 5 Monte Carlo simulations 81 5.1 The event generators 81 5.2 The detector simulation 84 5.2.1 The GEANT model for detector simulation 84 5.2.2 The ZG311T6 Monte Carlo programme 86 5.3 Beam gas scattering background to deep inelastic events . 87 5.4 Photoproduction as a background to deep inelastic events . 89 5.5 First level trigger studies and the generation of a second level input sample 90 6 Performance of the second level calorimeter trigger pro- cessor 95 6.1 A test set up using two 2TP-VME modules 95 6.2 Parameter values 98 6.3 Timing results 98 6.3.1 Layer 1 98 6.3.2 Layer 2 102 6.3.3 Estimates for layer 3 103 6.3.4 Estimates for data transport 104 ii 6.3.5 Conclusion 109 6.4 Implementation of the clustering algorithm in the ZEUS off- line reconstruction framework 110 6.5 Recognition of electrons in neutral current events 110 6.6 Recognition of parton jets in charged current events .... 113 6.7 Rejecting beam gas events using clusters 116 6.7.1 Timing of the calorimeter signals 116 6.7.2 High energy clusters at large polar angles 116 6.7.3 Trigger efficiency for non standard events 120 6.7.4 Combined results 121 6.7.5 Conclusion 121 6.8 Conclusion 121 A A buffering scheme for fixed length data items in OCCAM 123 B SASD description of the second level calorimeter trigger processor 127 B.I Introduction 127 B.2 The full scale implementation 127 B.2.1 The context diagram 127 B.2.2 The top level diagram 128 B.2.3 The layerl diagram 129 B.2.4 The Iayer2 diagram 130 B.2.5 The Iayer3 diagram 130 B.3 The two 2TP-VME module test set up implementation . 131 B.3.1 The context diagram 131 B.3.2 The top level diagram 132 B.3.3 The layerl diagram 132 B.3.4 The Iayer2 diagram 133 B.4 The off-line implementation in ZEPHYR 133 i References 135 • Acknowledgements 143 i Summary 145 Samenvatting 147 Hi List of Figures 1.1 HERA in the Volkspark in Hamburg 2 1.2 Artistic view on ZEUS 3 2.1 HERA schematic top view 6 2.2 HERA coordinate system 7 2.3 General lepton proton interaction at HERA 8 2.4 Polar diagram of HERA kinematics 10 2.5 Electron quark scattering 11 2.6 Electron gluon scattering 12 2.7 QCD Compton scattering 17 2.8 QED Compton scattering 18 2.9 Two and three jet cross sections 18 2.10 Prompt photon inclusive cross section 19 2.11 Charm and bottom pair production through photon gluon fusion 20 2.12 Top production through boson gluon fusion 20 3.1 Cut along the beam through ZEUS 28 3.2 Perpendicular cut through ZEUS 29 3.3 Wire layout in the CTD 31 3.4 Layout of one FTD chamber 31 3.5 CTD and FTD tracking resolution 32 3.6 Electron hadron separation by dE/dx 32 3.7 Electron hadron separation by the TRD 33 3.8 Electron hadron separation by the HES 35 3.9 Combined electron hadron separation for jets in the FCAL 35 3.10 Combined electron hadron separation for jets in the BCAL 36 3.11 A NC event in ZEUS 37 3.12 A heavy flavour event in ZEUS 38 3.13 A beam gas background event in ZEUS 39 3.14 Cut in the y — z plane through the calorimeter 39 3.15 The largest FCAL module 40 3.16 A BCAL module 42 3.17 Outline of the ZEUS DAQ 44 3.18 Schematic of the front end calorimeter electronics 45 3.19 PM signal before and after shaping 46 3.20 Dead time introduced by DSP processing 48 3.21 Supertower definition 49 4.1 FT distribution in jets from e+e~ annihilation 57 4.2 Pfn and P%ut in e+e~ annihilation 57 4.3 Transverse energy distribution inside jets in pseudo-rapidity from pp scattering 58 4.4 Lateral energy profile for hadrons in the calorimeter .... 59 4.5 T800 block diagram 63 4.6 Block diagram of the NIKHEF 2TP-VME module 65 4.7 Crate assignment to FCAL regions 71 4.8 Crate assignment to RCAL regions 71 4.9 Crate assignment to BCAL regions 72 4.10 Trigger network 72 4.11 HAC coordinates in the FCAL 75 4.12 Memory map for pre-clusters 79 5.1 Beam gas ET spectrum 84 5.2 Beam gas event activity as a function of Zvertex 88 5.3 Charged current event sample contamination with photon gluon fusion events 89 5.4 ET versus E^'"irt9 for various event types 92 6.1 SLCTP test set up 96 6.2 Layer 1 timings for the FCAL regions 100 6.3 Layer 1 timings for the BCAL and RCAL regions 101 6.4 Layer 2 timings for part of the FCAL 102 6.5 Layer 3 timings for part of the FCAL 104 6.6 Pre-clusters produced in layer 1 for the FCAL regions ... 106 6.7 Pre-clusters produced in layer 1 for the FCAL regions . 107 6.8 Clusters produced by layer 2 for the FCAL regions 108 6.9 Angular and energy difference for electrons and clusters . 112 6.10 Angular and energy difference for jets and clusters 114 6.11 Scatter plots of 9 versus E for dust sis 117 6.12 Clusters at largest angle from the beam 119 6.13 Charged current events lost by the cluster criterion 120 A.I FIFO buffer implemented as a process chain in OCCAM . 123 VI A.2 FIFO buffer implementation for long data items in OCCAM 124 B.I Full scale context diagram 128 B.2 Full scale top level diagram 128 B.3 Full scale layer 1 diagram 129 B.4 Full scale layer 2 diagram 130 B.5 Full scale layer 3 diagram 131 B.6 Two 2TP module test set up context diagram 131 B.7 Two 2TP module test set up top level diagram 132 B.8 Two 2TP module test set up layer 1 diagram 133 B.9 Two 2TP module test set up layer 2 diagram 134 B.10 Off-line implementation structure chart 134 :t Vll A/iii List of Tables 2.1 Parameters of the HERA collider 7 2.2 Photon gluon fusion cross sections 16 2.3 QCD Compton cross sections 17 4.1 Transputer link transmission speed as a function of cable length 64 4.2 Transputer cycle timing on the final 2TP-VME module .