Gabriele Cosmo
227 lines
10 KiB
Plaintext
227 lines
10 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Example HGCal_testbeam
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----------------------
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This example is based on the Geant4 standalone application developed
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by Thorben Quast for the CMS HGCal studies:
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https://github.com/ThorbenQuast/HGCal_TB_Geant4.
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The goal of this example is to demonstrate a test beam setup used
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in HEP experiments, and as a base for the validation studies and
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comparison with experiment data.
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It presents a test beam setup used in the HGCal studies in October
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2018. It can be easily extended to other configurations.
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Details on the High Granularity Calorimeter (HGCal) can be found
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i.a. in the Technical Design Report:
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https://cds.cern.ch/record/2293646/files/CMS-TDR-019.pdf
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1. Detector description
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-----------------------
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Detector construction in this example assumes that the setup is
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constructed with different elements placed one behind another along
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z axis (beam axis).
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There are 3 configurations user can choose from, and could be set
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with UI command:
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/HGCalTestbeam/setup/configuration <ID>
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where <ID> by default is equal to 0, which means the HGCal testbeam
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setup used in October 2018.
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<ID> 1 builds the same calorimeter setup, but places in front of it
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several beamline elements.
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<ID> 2 builds a very simplistic test configuration.
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Whenever a silicon wafer or SiPM is placed in the detector, a sensitive
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volume is attached to it, and will be used to collect signal.
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Silicon wafer is divided into cells (pixels), and each individual pixel
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can collect signal.
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In order to change the maximum step size allowed in silicon pixels:
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/HGCalTestbeam/setup/stepSilicon <STEP>
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where <STEP> is value of the max step size in micrometres. By default
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<STEP> is equal to 30 um.
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2. Signal
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---------
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Energy deposited within silicon pixels and SiPMs is registered in the
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sensitive detectors. Each deposit is added individually to the vector
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of hits, in order to allow the digitisation.
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Digitisation is performed at the end of the event. It accumulates the
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energy deposits within pixels, taking into account the time cut on the
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arrival of signal (global time of energy deposit). By default no time
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cut is applied which means all the deposits are counted. It can be set
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using UI command:
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/HGCalTestbeam/hits/timeCut <TIME>
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where <TIME> is the maximum global time of the energy deposit that
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would be counted into the signal within the pixel.
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Another hit parameter is TOA (time of arrival) which is calculated
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as time of the energy deposit which added to the digitised pixel energy
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exceeds the threshold. By default the threshold is equal to 0, which
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means that any hit will exceed the value, so TOA of pixel equals to
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the time of the first energy deposit. It can be set using UI command:
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/HGCalTestbeam/hits/toaThreshold <ENERGY_THRESHOLD>
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where <ENERGY_THRESHOLD> indicates the threshold the sum of energy
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needs to exceed to be counted as time of arrival.
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Additionally, for silicon pixels, time of the last energy deposit
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(within the time window) is recorded.
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3. Output
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---------
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Output with event signal is stored in ntuple and saved to a ROOT file.
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Its name can be set with UI command:
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/HGCalTestbeam/output/file <NAME>
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Created TTree "hits" contains following branches:
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+---------------------------------+-----------------+------+-------------------------------------------+
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| Branch | Type | Unit | Description |
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+---------------------------------+-----------------+------+-------------------------------------------+
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| event | int | - | |
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| pdgID | vector<int> | - | PDG code of primary particles |
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| beamEnergy | vector<double> | GeV | initial energy of primaries |
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| beamX_cm | vector<double> | cm | initial X position of primaries |
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| beamY_cm | vector<double> | cm | initial Y position of primaries |
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| beamZ_cm | vector<double> | cm | initial Z position of primaries |
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| siliconHits_ID | vector<int> | - | ID of hits in Si (=1e3*waferID+cellID) |
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| siliconHits_x_cm | vector<double> | cm | X position of Si pixel |
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| siliconHits_y_cm | vector<double> | cm | Y position of Si pixel |
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| siliconHits_z_cm | vector<double> | cm | Z position of Si pixel |
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| siliconHits_Edep_keV | vector<double> | keV | energy deposited within Si pixel |
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| siliconHits_EdepNonIonizing_keV | vector<double> | keV | non-ionizing energy deposit (Si) |
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| siliconHits_TOA_ns | vector<double> | ns | time of arrival for Si pixel |
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| siliconHits_TOA_last_ns | vector<double> | ns | time of last arrival for Si pixel |
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| siliconHits_type | vector<int> | - | hit type for Si pixel (=0) |
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| SiPMHits_ID | vector<int> | - | ID of hits in SiPM (=1e3*sensorID+cellID) |
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| SiPMHits_x_cm | vector<double> | cm | X position of SiPM |
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| SiPMHits_y_cm | vector<double> | cm | Y position of SiPM |
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| SiPMHits_z_cm | vector<double> | cm | Z position of SiPM |
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| SiPMHits_Edep_keV | vector<double> | keV | energy deposited within SiPM |
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| SiPMHits_EdepNonIonizing_keV | vector<double> | keV | non-ionizing energy deposit (SiPM) |
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| SiPMHits_TOA_ns | vector<double> | ns | time of arrival for SiPM |
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| SiPMHits_type | vector<int> | - | hit type for SiPM (= 1) |
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| signalSum_HGCAL_GeV | double | GeV | sum of energy deposited in Si pixels |
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| COGZ_HGCAL_cm | double | cm | energy-weighted shower depth in z |
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| NHits_HGCAL | int | - | number of Si pixel hits |
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| signalSum_AHCAL_GeV | double | GeV | sum of energy deposited in SiPMs |
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| COGZ_AHCAL_cm | double | cm | energy-weighted shower depth in z |
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| NHits_AHCAL | int | - | number of SiPM hits |
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+---------------------------------+-----------------+------+-------------------------------------------+
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4. Primary particle generator
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-----------------------------
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Particle gun is used as a default primary particle generator.
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It can be controlled with standard UI commands (/gun/) and with
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additional ones introduced by the messenger:
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/HGCalTestbeam/generator/momentumSpread <VALUE>
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to change constant particle energy to Gaussian distribution with
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sigma expressed in units of the initial energy (e.g. <VALUE>=0.05
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means sigma of 0.05 * E). By default it equals to 0 and constant
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energy value is used.
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/HGCalTestbeam/generator/beamSpread <none/Gaussian/flat>
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to define type of beam position spread. By default none is used.
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/HGCalTestbeam/generator/beamSpreadX <SIZE>
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to define size of beam spread along x axis. It is sigma of a
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Gaussian distribution, or half-width of a flat distribution.
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/HGCalTestbeam/generator/beamSpreadY <SIZE>
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to define size of beam spread along y axis. It is sigma of a
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Gaussian distribution, or half-width of a flat distribution.
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/HGCalTestbeam/generator/fBeamZ0 <POSITION>
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to define beam position along z axis. By default edge of the
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world volume is used.
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Additionally, if installation was done with ROOT package (CMake
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was able to locate it), an option of input read from the ROOT file
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is enabled. It can be activated with
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/HGCalTestbeam/generator/fReadInputFile true
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/HGCalTestbeam/generator/fPathInputFile <FILE>
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sets the path to the input file.
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/HGCalTestbeam/generator/startFromEvent <N>
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allows to start simulation from Nth event.
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Please note that in current implementation input from file needs to be
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executed in a non-multithreaded mode (or with 1 thread).
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Input file needs to have following structure:
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- TDirectory "VirtualDetector"
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- TNtuple "HGCAL" with branches:
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+---------+-------+------+-------------------------------+
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| Branch | Type | Unit | Description |
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+---------+-------+------+-------------------------------+
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| EventID | float | - | ID of event |
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| PDGid | float | - | Particle type (PDG code) |
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| x | float | mm | Initial X position |
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| y | float | mm | Initial Y position |
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| Px | float | MeV | Initial momentum along X axis |
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| Py | float | MeV | Initial momentum along Y axis |
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| Pz | float | MeV | Initial momentum along Z axis |
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+---------+-------+------+-------------------------------+
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Several particles may belong to the same event, in which case all
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of them are read from the input file.
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Z position is set to Z position of the entrance of the HGCal detector.
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5. How to run the example
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-------------------------
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Example can be run in interactive mode, with visualisation:
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./HGCal_testbeam
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It will execute init_vis.mac and vis.mac.
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To run in a batch mode, specify the path to the macro:
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./HGCal_testbeam run.mac
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which will run 10 single-electron events, with beam energy of 30 GeV.
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The beam position is smeared with Gaussian with x/y sigma of 1.5 cm.
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The momentum is smeared with Gaussian with sigma of 5% (2.5 GeV).
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Z beam position is set to -1 m.
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Maximum step size in Si pixel is 20 um.
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The name of the created file is output_eM_smeared_30GeV_10events.root.
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6. Additional settings
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----------------------
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6.1. Particle input from ROOT file
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----------------------------------
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If ROOT is found by CMake, it allows to use ROOT file as the input to
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the primary generator. See more in the description of "4. Primary
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particle generator".
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./HGCal_testbeam readFromFile.mac
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Macro readFromFile.mac can be used but name of the input file should
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be specified (not provided with the example). This mode is meant to
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be used in the validation with experimental data with geant-val. |