NU JPsi Simulations

Quick Start

1. Copy /work/halld/home/sdobbs/jpsi_mc
2. To load software configurations, use setup_jlab.csh script, e.g., "source setup_jlab.csh"
3. Optional, check out your own copy of latest software and build it:
   1. HDDS geometry package: svn co https://halldsvn.jlab.org/repos/trunk/hdds
   2. sim-recon: svn co https://halldsvn.jlab.org/repos/trunk/sim-recon
   3. Designate local build area by setting HALLD_MY
   4. J/psi event generator: svn co https://halldsvn.jlab.org/repos/trunk/home/sdobbs/bggen_jpsi - place in local build area
4. 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 and using Br(J/psi -> e+e- ) = 6%
  • 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
• Pions
  • gamma p -> p pi+ pi-, select rho events

Other important studies include:

• Rate at which correct beam photon is selected

Final goals

• Extraction of J/Psi cross sections as function of E(beam) and -t
• Efficiency v. purity for different E/p cuts