Making ideal simulations

Here are short notes on how to generate simulated ESDs for an ideal Muon spectrometer. The context is to get input data to compute a quick acceptance times effiency correction, possibly online (in Amore for Run2 or in whatever for Run3).

The setup is to use $ALICE_PHYSICS/PWG/muondep/AliMuonAccEffSubmitter :

AliMuonAccEffSubmitter a("GenJPsi13TeV",kFALSE,"4_25",800000,4000);
a->SetRemoteDir("/alice/cern.ch/user/l/laphecet/IdealSimulations5");
a->SetRunList(228936);
a->SetAliPhysicsVersion("VO_ALICE@AliPhysics::v5-08-13o-01-1");
a->Run("localtest");
a->Run("full");

Note that this will create (if not already done otherwise) OCDB snapshots in the local directory ./OCDB/228396/. Those snapshots are automatically generated (see class AliMuonOCDBSnapshotGenerator) from a local OCDB created by the submitter in ./OCDB with default objects for Config, Pedestals, OccupancyMap, HV,LV, RejectList. The other objects in the snapshots are taken directly from the raw:// OCDB (or any OCDB the submitter is configured with by the SetOCDBPath method), except the RecoParam which is patched to remove the cut on any of the defaults objects in the local OCDB (the idea being to produce an ideal but realistic simulation, as far as geometry, alignment, tracking and trigger parameters are concerned).

The produced ESDs (on the grid) are then processed to “compact” them as much as possible, using the ConvertESD function in QuickAccEff.C using a little script :

#!/bin/sh

echo "root -b <<EOF"
echo ".L /source/QuickAccEff.C+"

for file in $(find /data/simulations/FromHugoAndAstrid13TeVConfig -name AliESDs.root)
do
    dest=${file/AliESDs/compact}
    echo "ConvertESD(\"$file\",\"$dest\");"
    done
echo "EOF"

And the compact files are then packed together into a single one :

hadd compact.root $(find . -name 'compact*' | tr "\n" " ")

To get an idea, making a simulation of 796k J/psi (800000 intended but one grid job failed and I did not bother resubmiting it) leads to about 6GB of ESDs :

~/mchoncall/simulations/FromHugoAndAstrid13TeVConfig
❯ du -ch */AliESDs.root
...
32M    196/AliESDs.root
32M    197/AliESDs.root
32M    198/AliESDs.root
32M    199/AliESDs.root
32M    200/AliESDs.root
6,1G    total

and once compacted the ~330k events remaining are shrinked to 45MB :

❯ du -ch compact.root
45M    compact.root