| Geant4 Cross Reference |
1 ------------------------------------------------------------------- 2 3 ========================================================= 4 Geant4 - an Object-Oriented Toolkit for Simulation in HEP 5 ========================================================= 6 7 Example HGCal_testbeam 8 ---------------------- 9 10 This example is based on the Geant4 standalone application developed 11 by Thorben Quast for the CMS HGCal studies: 12 https://github.com/ThorbenQuast/HGCal_TB_Geant4. 13 14 The goal of this example is to demonstrate a test beam setup used 15 in HEP experiments, and as a base for the validation studies and 16 comparison with experiment data. 17 18 It presents a test beam setup used in the HGCal studies in October 19 2018. It can be easily extended to other configurations. 20 21 Details on the High Granularity Calorimeter (HGCal) can be found 22 i.a. in the Technical Design Report: 23 https://cds.cern.ch/record/2293646/files/CMS-TDR-019.pdf 24 25 1. Detector description 26 ----------------------- 27 28 Detector construction in this example assumes that the setup is 29 constructed with different elements placed one behind another along 30 z axis (beam axis). 31 There are 3 configurations user can choose from, and could be set 32 with UI command: 33 34 /HGCalTestbeam/setup/configuration <ID> 35 36 where <ID> by default is equal to 0, which means the HGCal testbeam 37 setup used in October 2018. 38 <ID> 1 builds the same calorimeter setup, but places in front of it 39 several beamline elements. 40 <ID> 2 builds a very simplistic test configuration. 41 42 Whenever a silicon wafer or SiPM is placed in the detector, a sensitive 43 volume is attached to it, and will be used to collect signal. 44 45 Silicon wafer is divided into cells (pixels), and each individual pixel 46 can collect signal. 47 48 In order to change the maximum step size allowed in silicon pixels: 49 50 /HGCalTestbeam/setup/stepSilicon <STEP> 51 52 where <STEP> is value of the max step size in micrometres. By default 53 <STEP> is equal to 30 um. 54 55 2. Signal 56 --------- 57 58 Energy deposited within silicon pixels and SiPMs is registered in the 59 sensitive detectors. Each deposit is added individually to the vector 60 of hits, in order to allow the digitisation. 61 62 Digitisation is performed at the end of the event. It accumulates the 63 energy deposits within pixels, taking into account the time cut on the 64 arrival of signal (global time of energy deposit). By default no time 65 cut is applied which means all the deposits are counted. It can be set 66 using UI command: 67 68 /HGCalTestbeam/hits/timeCut <TIME> 69 70 where <TIME> is the maximum global time of the energy deposit that 71 would be counted into the signal within the pixel. 72 73 Another hit parameter is TOA (time of arrival) which is calculated 74 as time of the energy deposit which added to the digitised pixel energy 75 exceeds the threshold. By default the threshold is equal to 0, which 76 means that any hit will exceed the value, so TOA of pixel equals to 77 the time of the first energy deposit. It can be set using UI command: 78 79 /HGCalTestbeam/hits/toaThreshold <ENERGY_THRESHOLD> 80 81 where <ENERGY_THRESHOLD> indicates the threshold the sum of energy 82 needs to exceed to be counted as time of arrival. 83 84 Additionally, for silicon pixels, time of the last energy deposit 85 (within the time window) is recorded. 86 87 3. Output 88 --------- 89 90 Output with event signal is stored in ntuple and saved to a ROOT file. 91 Its name can be set with UI command: 92 93 /HGCalTestbeam/output/file <NAME> 94 95 Created TTree "hits" contains following branches: 96 97 +---------------------------------+-----------------+------+-------------------------------------------+ 98 | Branch | Type | Unit | Description | 99 +---------------------------------+-----------------+------+-------------------------------------------+ 100 | event | int | - | | 101 | pdgID | vector<int> | - | PDG code of primary particles | 102 | beamEnergy | vector<double> | GeV | initial energy of primaries | 103 | beamX_cm | vector<double> | cm | initial X position of primaries | 104 | beamY_cm | vector<double> | cm | initial Y position of primaries | 105 | beamZ_cm | vector<double> | cm | initial Z position of primaries | 106 | siliconHits_ID | vector<int> | - | ID of hits in Si (=1e3*waferID+cellID) | 107 | siliconHits_x_cm | vector<double> | cm | X position of Si pixel | 108 | siliconHits_y_cm | vector<double> | cm | Y position of Si pixel | 109 | siliconHits_z_cm | vector<double> | cm | Z position of Si pixel | 110 | siliconHits_Edep_keV | vector<double> | keV | energy deposited within Si pixel | 111 | siliconHits_EdepNonIonizing_keV | vector<double> | keV | non-ionizing energy deposit (Si) | 112 | siliconHits_TOA_ns | vector<double> | ns | time of arrival for Si pixel | 113 | siliconHits_TOA_last_ns | vector<double> | ns | time of last arrival for Si pixel | 114 | siliconHits_type | vector<int> | - | hit type for Si pixel (=0) | 115 | SiPMHits_ID | vector<int> | - | ID of hits in SiPM (=1e3*sensorID+cellID) | 116 | SiPMHits_x_cm | vector<double> | cm | X position of SiPM | 117 | SiPMHits_y_cm | vector<double> | cm | Y position of SiPM | 118 | SiPMHits_z_cm | vector<double> | cm | Z position of SiPM | 119 | SiPMHits_Edep_keV | vector<double> | keV | energy deposited within SiPM | 120 | SiPMHits_EdepNonIonizing_keV | vector<double> | keV | non-ionizing energy deposit (SiPM) | 121 | SiPMHits_TOA_ns | vector<double> | ns | time of arrival for SiPM | 122 | SiPMHits_type | vector<int> | - | hit type for SiPM (= 1) | 123 | signalSum_HGCAL_GeV | double | GeV | sum of energy deposited in Si pixels | 124 | COGZ_HGCAL_cm | double | cm | energy-weighted shower depth in z | 125 | NHits_HGCAL | int | - | number of Si pixel hits | 126 | signalSum_AHCAL_GeV | double | GeV | sum of energy deposited in SiPMs | 127 | COGZ_AHCAL_cm | double | cm | energy-weighted shower depth in z | 128 | NHits_AHCAL | int | - | number of SiPM hits | 129 +---------------------------------+-----------------+------+-------------------------------------------+ 130 131 4. Primary particle generator 132 ----------------------------- 133 134 Particle gun is used as a default primary particle generator. 135 It can be controlled with standard UI commands (/gun/) and with 136 additional ones introduced by the messenger: 137 138 /HGCalTestbeam/generator/momentumSpread <VALUE> 139 to change constant particle energy to Gaussian distribution with 140 sigma expressed in units of the initial energy (e.g. <VALUE>=0.05 141 means sigma of 0.05 * E). By default it equals to 0 and constant 142 energy value is used. 143 144 /HGCalTestbeam/generator/beamSpread <none/Gaussian/flat> 145 to define type of beam position spread. By default none is used. 146 147 /HGCalTestbeam/generator/beamSpreadX <SIZE> 148 to define size of beam spread along x axis. It is sigma of a 149 Gaussian distribution, or half-width of a flat distribution. 150 151 /HGCalTestbeam/generator/beamSpreadY <SIZE> 152 to define size of beam spread along y axis. It is sigma of a 153 Gaussian distribution, or half-width of a flat distribution. 154 155 /HGCalTestbeam/generator/fBeamZ0 <POSITION> 156 to define beam position along z axis. By default edge of the 157 world volume is used. 158 159 Additionally, if installation was done with ROOT package (CMake 160 was able to locate it), an option of input read from the ROOT file 161 is enabled. It can be activated with 162 163 /HGCalTestbeam/generator/fReadInputFile true 164 165 /HGCalTestbeam/generator/fPathInputFile <FILE> 166 sets the path to the input file. 167 168 /HGCalTestbeam/generator/startFromEvent <N> 169 allows to start simulation from Nth event. 170 171 Please note that in current implementation input from file needs to be 172 executed in a non-multithreaded mode (or with 1 thread). 173 174 Input file needs to have following structure: 175 - TDirectory "VirtualDetector" 176 - TNtuple "HGCAL" with branches: 177 +---------+-------+------+-------------------------------+ 178 | Branch | Type | Unit | Description | 179 +---------+-------+------+-------------------------------+ 180 | EventID | float | - | ID of event | 181 | PDGid | float | - | Particle type (PDG code) | 182 | x | float | mm | Initial X position | 183 | y | float | mm | Initial Y position | 184 | Px | float | MeV | Initial momentum along X axis | 185 | Py | float | MeV | Initial momentum along Y axis | 186 | Pz | float | MeV | Initial momentum along Z axis | 187 +---------+-------+------+-------------------------------+ 188 189 Several particles may belong to the same event, in which case all 190 of them are read from the input file. 191 Z position is set to Z position of the entrance of the HGCal detector. 192 193 5. How to run the example 194 ------------------------- 195 196 Example can be run in interactive mode, with visualisation: 197 198 ./HGCal_testbeam 199 200 It will execute init_vis.mac and vis.mac. 201 202 To run in a batch mode, specify the path to the macro: 203 204 ./HGCal_testbeam run.mac 205 206 which will run 10 single-electron events, with beam energy of 30 GeV. 207 The beam position is smeared with Gaussian with x/y sigma of 1.5 cm. 208 The momentum is smeared with Gaussian with sigma of 5% (2.5 GeV). 209 Z beam position is set to -1 m. 210 Maximum step size in Si pixel is 20 um. 211 The name of the created file is output_eM_smeared_30GeV_10events.root. 212 213 6. Additional settings 214 ---------------------- 215 216 6.1. Particle input from ROOT file 217 ---------------------------------- 218 219 If ROOT is found by CMake, it allows to use ROOT file as the input to 220 the primary generator. See more in the description of "4. Primary 221 particle generator". 222 223 ./HGCal_testbeam readFromFile.mac 224 225 Macro readFromFile.mac can be used but name of the input file should 226 be specified (not provided with the example). This mode is meant to 227 be used in the validation with experimental data with geant-val.