FairShip simulation

Finally starting to do some physics here

Simulation for Charm cross section and Muon flux measurements

Charmdet folder contains the geometry classes for the detectors used in charm cross section and Muon flux measurements.

Simulations for charm cross section measurement

In general:

Option --CharmdetSetup 1 activates charm cross section geometry, while --CharmdetSetup 0 activates muon flux geometry.

Only the most useful options have been explained here. For the complete list of available options please refer to the related scripts.

No particular cuts are usually done with the respect to the Default FairShip phyisics options. However, by default for hit with kinetic energy lower than 100 MeV the software will NOT save the MCTrack, to avoid memory consumption. If tracks with lower energy need to be studied, this threshold can be lowered in the simulation script. To do that, put MCTracksWithEnergyCutOnly = False in macro/run_simScript.py and launch the simulation with -F option (deepcopy).

FairShip used cuts are shown in gconfig/SetCuts.C. Energy thresholds for interactions are usually 1 MeV

Charm production simulations are done from macro/run_simScript.py. Example syntax: python $FAIRSHIP/macro/run_simScript.py --charm 1 -A charmonly --CharmdetSetup 1 -f Cascadefile -n 1000 -o outputfolder

My current simulation configuration (charsim branch):

python /afs/cern.ch/work/a/aiuliano/public/SHIPBuild/FairShip/macro/run_simScript.py --charm 1 -A charmonly --CharmdetSetup 1 -f $INPUTFILE --CharmTarget 1 --TrackingCharm -n $NEVENTS -i $STARTEVENT -o $OUTPUTDIR/simulation/$ProcId

Useful options:

  • --charm 1: activates charmdet configuration instead of SHiP standard (both

    for charm cross section and muon flux measurements)

  • -A charmonly: activates

    charm production simulation

  • -f: input file with charm vertices (if you have Kerberos configured (e.g.

    by default on lxplus), this will be taken directly

    from /eos/ship/data/Charm/Cascade-parp16-MSTP82-1-MSEL4-978Bpot.root by

    default)

  • -n: number of events

  • -o: output of folder where geometry and output of simulation will be saved

General POT simulations are done from muonShieldOptimization/run_MufluxfixedTarget.py. Example of syntax:

python $FAIRSHIP/muonShieldOptimization/run_MufluxfixedTarget.py --CharmdetSetup 1 -G -e 0.001 -n 1000 -o outputfolder

My current simulation configuration (charsim branch):

python $FAIRSHIP/muonShieldOptimization/run_MufluxfixedTarget.py --CharmdetSetup 1 --CharmTarget 1 -G -e 0.1 -n $NEVENTS -o $OUTPUTFOLDER/$ProcId

It is a derivation of the fixed target simulation used in SHiP, applied to charmdet geometry.

Useful options:

  • -e: Energy cut for adding tracks to Geant4 propagation (choosing a high cut

    allows to save memory for larger simulations)

  • -n: Number of events

  • -o: output of folder where geometry and output of simulation will be saved

  • -r: number of run (can be used as folder naming if -o option is not used)

  • -f : force overwriting of directory (DANGEROUS: if used in a wrong

    directory, it will delete it. DO NOT USE IT together with -o option)

Different options for proton generation:

  • -V: default one, proton interactions generated with Pythia and EvtGen is

    used for decays

  • -P: both proton interactions and decays handled with Pythia

  • -G: most basic simulation: one 400 GeV proton directly sent to Geant4

Details can be found here:

All simulations use Geant4 for propagation. IMPORTANT: Both -V and -P generate all interactions in target. Due to small dimensions of target used in charmdet measurement, many protons pass through without interacting. To correctly simulate surviving protons and their tracks in detectors, use -G option.

For any question or doubt about these simulations, contact Thomas Ruf (mailto:thomas.ruf@cern.ch) or Antonio Iuliano (mailto:antonio.iuliano@cern.ch)

Index of MCTrackID definitions

First, charm simulation: each event produced two charmed hadrons, charm and anti-charm. Their IDs depends on what was passed to Geant4 within the simulation:

  • Default configuration, charmed hadrons, decay daughters and other primaries passed from Pythia to Geant4: the first charmed hadron has MCTrackID 1 and MCMotherID 0, the other primary particles have MCMotherID -1, the ID of the second charmed hadron is not fixed (it has be to looked from its pdgcode). Charm decay daughters can contain intermediate states;

  • Test configuration for charmed hadron's propagations (--TrackingCharm), charmed hadrons and other primary particles passed from Pythia to Geant4: charmed hadrons have MCTrackIDs 1 and 2 ( and MCMotherID 0), other primaries have MCMotherID -1. Charm decay daughters should not contain intermediate states;

  • Proton background simulation (G4 only): a single 400-GeV proton is passed to Geant4 for propagation and interaction. The produced particles have mother ID 0. Need to select ProcID 23 to study daughters of hadronic inelastic interactions.

Making charm (and beauty) hadron cascades

The macro/MakeCascade.pyscript is a stand-alone simulation (i.e. it not uses TGeo either TVirtualMC) with a tuned version of Pythia6. It will simulate the production of charm or beauty hadrons, also simulating cascade production from hadrons. It has the following options:

  • -n for number of events to simulate;

  • -m to choose between charm and beauty production (default charm);

  • -E for beam energy in GeV (default 400);

  • -t name of output file;

  • -s for seed (by default it uses current time);

  • -P to store all particles produced together with charm (mostly needed in our emulsion reconstruction studies);

Also, it is not an option, but it uses the fraction of proton in nucleus to simulate interactions on proton or neutron in Pythia: by default it uses molybednum (0.43), but I often change it to lead (0.40).

Moreover, in very small targets the cascade leads to unphysical peaks at the end of the target (in the following FairShip simulation). To avoid that, I select only primary charm k==1 from the produced tree, given k an integer number representing cascade depth

The script macro/makeDecay.py makes the charm hadron decays, to save muon and neutrino spectra. I have added a modified version to compare the spectra with k==1 and k>1 (in charmsim branch). Attention: Ds are not correctly handled by Pythia6, which produces more hadrons than expected, makeDecay will report the difference at the end, usually a factor 7.7/10.6. The comparison of neutrino fluxes is done by $SHIPMACROS/testscripts/neutrino_fluxes_cascade.C

Simulations for muon flux measurements

  • For full simulation, proton (400 GeV) on SHiP muflux target, plus detector setup:

    python run_MufluxfixedTarget.py -e ecut -P --CharmdetSetup 0

    more options available (boosting di-muon BR, di-muon cross sections,

    charmonium, charm, ...), see --help

  • For fast simulation, with muons from external file:

    `python run_simScript.py --MuonBack -n 1000 --charm=1 --CharmdetSetup=0 -f

    inputFile, whereinputFile`:

    /eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_10.0_withCharmandBeauty0_mu.root

    (+ 66 more files)

  • For digitization:

    `python runMufluxDigi.py -f ship.conical.FixedTarget-TGeant4.root -g

    geofile_full.conical.FixedTarget-TGeant4.root`→

    ship.conical.FixedTarget-TGeant4_dig.root Track reconstruction & analysis use

    drifttubeMonitoring.py, will automatically detect if it is MC data.

Simulation for neutrino interactions

run_simScript.py has a cut on kinetic energy, by default set at 100 MeV, to avoid to produce too heavy files (space is precious). Particles with lower energy are produced, but only the hits are saved (we lose MCTrack information). This can be changed at line 33, by setting MCTracksWithHitsOnly = False and MCTracksWithHitsOrEnergyCut = True

Neutrino interactions are simulated with GENIE MonteCarlo software, then the produced particles are sent to Geant4 for propagation. Starting from the 2018 spectra produced by Thomas, they can be found in:

  • /eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_charm_nu_1.0.root

  • /eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_charm_nu_10.0.root

The neutrino spectra in these files are weighted to 5E13 pot, which roughly amount to a SPS spill. ShipSoft presentation of March 2018 explain the details of this production.

Thomas has updated the files, so now they match correctly. I can use the 1.0 file without any issue.

In this file you can find 1D histogram of neutrino momentum, along with 2D histograms of pt vs p. The 1D histograms are the input for GENIE, while the 2D ones will be used by FairShip generator to generate in the transverse plane.

Genie simulation

Most of this material here is credit to Annarita.

First (and important!), we need to set Genie User Decay Settings, to tell Genie not to make tau leptons and charmed hadrons decay, because we want to let Geant4 decay them.

This is set in UserPhysicsOption.xml, setting the option DecayParticlewithCode = pdgcode, as false, with pdg codes for charmed hadrons:

  • ± 421

  • ± 411

  • ± 431

  • 4122

  • 4112

  • 4212

  • 4222

and for tau leptons:

  • ± 16

Export GXMLPATH variable with the path of the modified UserPhysicsOptions.xml will tell Genie your request.

If you do not have splines, you have to create them by launching

gmkspl -p #nu -t 1000822040[0.014], 1000822060[0.241], 1000822070[0.221], 1000822080[0.524] -n 500 -e 400 -o out_file_name.xml

I am currently using Annarita splines. Actually Genie manual does not recommend that, but to use official splines if no particular physical requests are asked. I did not see any difference last time I checked with the official splines. I will probably use official splines for future generations (not current ones)

Launch Genie simulations with:

gevgen -n Nevents -p neutrinocode -t targetcode -e 0.5,350 --run nrun -f neutrinofile,histoname --cross-sections splines --message-thresholds $GENIE/config/Messenger_laconic.xml --seed nseed

Convert the output in gst format:

gntpc -i gntp.0.ghep.root -f gst --message-thresholds $GENIE/config/Messenger_laconic.xml"

All these operations are written in macro/makeGenieEvents.py Usage: > python -i > makeEvent(100) > makeNtuples().

Input neutrino fluxes have been produced by Thomas, in the main proton on target simulation (the same which produces the muon spectra). The most recent ones are from 2018 and are in the following folder:

/eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_10.0_withCharm_nu.root (10 GeV cut)

/eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_1.0_withCharm_nu.root (1 GeV cut)

Both files are weighted to correspond to 1 proton spill ( 4×10134 \times 10^{13} protons on target).

2021 Update: I am currently producing the interactions in a tungsten target. Since tungsten was not in the official splines, I have produced the splines manually.

FairShip GenieGen simulation

FairShip run_simScript.py simulation with -Genie option launchs the GenieGen class in shipgen. The syntax is the following:

python $FAIRSHIP/macro/run_simScript.py --Genie -f nufluxfile.root -n nevents -o outputfolder

It will use the information about neutrino interaction from the Genie simulation to do the following steps:

  1. From p-pt association (2D spectra) and random generation of phi angles, obtain kinematic information of event.

  2. Place the interactions in the target (z randomly generated, x and y propagated from target according to angles)

  3. Compute a weight of the event, according to the density of material.

  4. Pass the weighted event to Geant4 for usual propagation and save of MC information

The weight is computed as ∑i(xi∗ρi)\sum_i(x_i*\rho_i) , from density of material and length transversed in material. In fact, it is related to the rate of interactions, according to the rate formula from the cross section:

R=Lσ=IρlNAAσ=IwNAAσR=L\sigma = I \frac{\rho l N_A}{A} \sigma = I \frac{wN_A}{A}\sigma

Indeed, we expect more interactions in more dense material (i.e. many in the lead, few in emulsion and very few in air gaps), but if you do not use the weight you will see the positions uniformly distributed there! Therefore, when plotting the hits always use weighted histograms. Weight is the same for all particles of the same events, so you can use MCTrack[0].GetWeight() to find it

By default, FairShip will generate neutrino interactions in a vast z region, because many detectors study neutrino interactions as a background source. Usually, we want to study only the interactions happening in the detector. We then set GenieGen positions as:

Geniegen.SetPositions(ship_geo.target.z0, ship_geo.NuTauTarget.zC-ship_geo.NuTauTarget.zdim/2, ship_geo.NuTauTarget.zC+ship_geo.NuTauTarget.zdim/2)

But this mostly depends on what we want to study and it should be kept under control

Also, remember to cut entries outside of Target, usually done with the cutsim.py code!

Simulation for muon background

Muon background is simulated with --MuonBack option from macro/run_simScript.py. It takes as input the muon fluxes produced by Thomas and stored in 67 large ROOT files ($N$ a number from 0 to 66):

/eos/experiment/ship/data/Mbias/background-prod-2018/pythia8_Geant4_10.0_withCharmandBeauty$N$000_mu.root

They are weighted, according to the production computing facility. The weights are transferred to the run_simScript simulation and are to be included in the histogram maps. Included weights, the muons correspond to the protons from one spill ( 4×10134 \times 10^{13} protons on target).

An excellent example of script to produce muon flux maps is the macro/flux_map.py script.

Checking geometry of a simulation

Every FairShip simulation produces a geometry file (named `geofile*.root`), along with the simulation tree file. This allows to check the status of the geometry at the time the simulation has been performed.

Launching the Event Display

FairShip itself uses an event display with the following syntax:

python -i $FAIRSHIP/macro/eventDisplay.py -f simulationfile.root -g geofile.root

Which opens a display of the whole detector, and it additionally offers a display of the events from the simulationfile. Being very slow, it is often useful to check the vislvl option in the script, at the following position (line 1061):

fMan.Init(1,4,10) # default Init(visopt=1, vislvl=3, maxvisnds=10000), ecal display requires vislvl=4

Increasing the vislvl allows to more subvolumes, but makes the EventDisplay even slower. To display events in a reasonable way, I usually launch a small partner simulation, with only the neutrino detector volumes active. This however must be taken with caution, because it is not guaranteed that partner simulation uses same geometry of original simulation.

Inspecting volume sizes and positions

Another important check is done by the getGeoInformation.py script:

python $FAIRSHIP/macro/getGeoInformation.py -g geofile.root -v myvolume -l nlevels

Positions in FairShip reference system and half-dimensions of all mother volumes are reported. myvolume is also expanded to show the daughters until nlevels. Moreover, the medium of the volume is reported

Before pushing new changes

Checking overlaps and extrusions

Changes in positions and/or dimensions of geometrical volumes may cause overlapping between two volumes or extrusions of a daughter node with respect to its mother node (i.e., it exits from the region covered by the mother volume).

Luckily, there is an automated tool to provide this check, and it should be launched as much frequently as possible (and ALWAYS before opening a pull request to ShipSoft master repository). At the start of macro/run_simScript.py, simply set debug flag to 2 instead of 0. It will report the magnetic fields at the start of the program, while at the end it will perform the overlap/extrusion check.

Backward-compatibility check

FairShip is not only used for launching simulations, but also for analyzing the results of them (providing reconstruction, even if unluckily is not implemented in our subdetectors). Therefore, after changing methods and attributes of some class, we must confirm that the program can still access old data without errors. To do that, follow this procedure, proposed by Thomas:

  1. Launch a simulation, then reconstruction and analysis with the master FairShip version (official repository):

python $FAIRSHIP/macro/run_simScript.py
python $FAIRSHIP/macro/ShipReco.py -f ship.conical.Pythia8-TGeant4.root -g geofile_full.conical.Pythia8-TGeant4.root
python -i $FAIRSHIP/macro/ShipAna.py -f ship.conical.Pythia8-TGeant4_rec.root -g geofile_full.conical.Pythia8-TGeant4.root

2. Read the produced data with the new compiled FairShip version, by launching analysis and reconstruction:

python -i $FAIRSHIP/macro/ShipAna.py -f ship.conical.Pythia8-TGeant4_rec.root -g geofile_full.conical.Pythia8-TGeant4.root
python $FAIRSHIP/macro/ShipReco.py -f ship.conical.Pythia8-TGeant4.root -g geofile_full.conical.Pythia8-TGeant4.root

Behaviour of neutral particles

Usually, you do not want to analyze hits from neutral particles, since they are not detected. Concerning the simulation, no charge check is applied. Instead, particle hits are excluded only if ELoss==0 , that means the particle hits are stored only if they leave a fraction of their energy in the detector. This is reasonable, since this is how in general a particle detector works. However, if the particle stops in the detector volume, it seems that all its energy is given to the volume, and ELoss is not 0 (probably to avoid violating energy conservation?).

This means that you will encounter a small number of neutral (photons, pi0, etc.) MCPoint in your simulation. That common rule is to exclude them at the analysis, by using TPDGDatabase interface.

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