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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.
