NU JPsi Simulations
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Contents
Quick Start
- Copy /work/halld/home/sdobbs/jpsi_mc
- To load software configurations, use setup_jlab.csh script, e.g., "source setup_jlab.csh"
- Optional, check out your own copy of latest software and build it:
- HDDS geometry package: svn co https://halldsvn.jlab.org/repos/trunk/hdds
- sim-recon: svn co https://halldsvn.jlab.org/repos/trunk/sim-recon
- Designate local build area by setting HALLD_MY
- J/psi event generator: svn co https://halldsvn.jlab.org/repos/trunk/home/sdobbs/bggen_jpsi - place in local build area
- Build/develop plugin: /work/halld/home/sdobbs/halld_my/plugins/ccbar_recon
Simulations
Example files are located at:
/work/halld/home/sdobbs/jpsi_mc/
The simulation chain looks like the following:
bggen_jpsi hdgeant mcsmear hdgeant.hddm hd_root -PPLUGINS=analysis_plugin hdgeant_smeared.hddm
Where
- bggen_jpsi generates the 4-vectors of the reaction. It is one of the many generator programs that does so. Its configuration file is "run_jpsi.ffr", which must be soft linked to "fort.15".
- hdgeant simulates the path of the generated particles through the detector using GEANT. Its configuration file is "control.in".
- mcsmear simulates the response of the detector
- hd_root is the main analysis program
Notes:
- When analyzing simulations (e.g. running hd_root) you should set the environment variable JANA_CALIB_CONTEXT in the following way: (setenv JANA_CALIB_CONTEXT "variation=mc")
- There's current a bug in the code for certain run values. The current example files use run 1501.
Analysis Plans
Initial goals
- 2-track invariant mass plots for
- all events
- as a function of E(beam)
- as a function of -t
- For a realistic event sample including J/psi, pi+pi-, and continuum e+e- events. Assume ratios of 4500:1 pi+pi-:J/psi events and X:1 e+e-:J/psi events, where J/psi events are defined as J/psi -> e+e- events
- Calculated rate assumes E(beam) > 8 GeV
- J/psi rate calculated by integrating default bggen beam flux with two-gluon exchange model cross sections stored in bggen_jpsi
- pi+pi- rate calculated by integrating default bggen beam flux with assumed constant pi+pi- cross section of 14.5 ub
- Note that this includes events for all M(pi+pi-) range, so these are dominated by rho -> pi+pi- decays.
- TODO: verify pythia model and/or use generator developed by Justin
- e+e- rate to be calculated
Further Studies
Major requirement of this analysis is to have E/p distributions agree between data and simulation, which demands matching of calorimeter energy deposition for electrons and pions. Here are some ideas to check this:
- Electrons
- photon -> e+e- conversions (FCAL only, probably)
- Select oppositely charged track pairs with invariant mass ~0, assuming electron mass, common vertex should be outside target volume
- pi0 -> gamma e+ e- Dalitz decay
- Select oppositely charged track pairs with invariant mass ~0, pair with photon, all three particles have invariant mass consistent with pi0 mass
- photon -> e+e- conversions (FCAL only, probably)
- Pions
- gamma p -> p pi+ pi-, select rho events
Final goals
- Extraction of J/Psi cross sections as function of E(beam) and -t
- Efficiency v. purity for different E/p cuts