Reconstruction, July 7, 2009

Time: 11:00 EST/10:00 CST

• See GlueX Communications for detailed instructions
• ESNET Number 8542553

Documents to Review

• Reconstruction References
• Reconstruction document in progress

Tentative Agenda

1. Reconstruction: Physics Reactions
2. Generating Background Events (Pythia: 124 μb @ 9GeV beam energy)
   • Shared data sets, filtering, et c.
3. Angular distributions in GlueXAmpTools? (seems to be flat regardless of spin, no structure in cosGJ - Blake)

Discussion

Reconstruction

• It is required that there are 4 photons showers and none are due to charged particles, this gives 6 possible combinations.
• Pi0 and Eta candidates are chosen as the eta-pi0 pair with the largest probability (from the fit)
• Before cuts ~51% of the generated events can be reconstructed. A cut on χ^2 < 3 leaves approximately 39% of generated events,

Pi0 and Eta masses the line in red is cutting on chi^2 < 3.

resonance mass

• a combination of a0(980), a2(1320), a0(1450), a4(2000) resonances.

missing mass

• the missing 4-momentum can be calculated from the eta, pi0, beam and target 4-momenta.

momentum transfer

Minutes

1. Matt suggested looking at the accept/reject code to determine whether this is causing the issues for flatness in cosGJ.
2. Mihajlo askked how many pairs of eta pi0 pass a chi^2 < 3 cut.
3. A discussion of how large data sets were in order to produce a common background data file. Blake looked at his bggen folders to find that a BGGEN hddm file is ~1kB/event (10^7 events is ~10GB) and an HDGEANT hddm file (from filtered BGGEN events) is ~27kB/event.