Ilya Selyuzhenkov May 20, 2008

Gamma-jet algorithm and isolation cuts:

1. Selecting only di-jet events identified by the STAR jet finder algorithm,
   with jets pointing opposite in azimuth:
   cos(phi_jet1 - phi_jet2) < -0.8

2. Select jet1 with a maximum neutral energy fraction (R_EM1).
   This is our gamma candidate, for which we further require:
   • No charge tracks associated with jet1 (default jet radius is 0.7):
     nChargeTracks_jet1 = 0
     Note, that this charge track veto only works
     in the EEMC region where we do have TPC tracking
   • No barrel towers associated with jet1 (pure EEMC jet):
     nBarrelTowers_jet1 = 0
   • Ratio of the energy in the 3x3 EEMC high tower cluster
     to the total jet energy to be:
     R_cluster>0.99 (previous, softer, cut was 0.9)

    

3. For the second jet2 (away side jet) we require:
   • That jet2 has at least ~10% of hadronic energy:
     R_EM2<0.9

    

4. Additional gamma candidate QA requirements:
   • Matching between EEMC SMD uv-strip cluster with a 3x3 cluster of EEMC towers.
     (in addition reject events for which we can not idetify uv-strip intersection)
   • Minimum number of strips in 5-strip EEMC SMD uv-plane clusters to be greater that 3.

Data sample:

• pp2006(long) - 2006 pp production longitudinal data after applying gamma-jet isolation cuts
  (note the new R_cluster>0.99 cut)

Shower shapes sorted by pre-shower, z-vertex and gamma's eta, phi, pt

Note, that all shapes are normalized at peak to unity

Figure 1:Shower shapes for different detector eta bins

Figure 2:Shower shapes for different detector phi bins

Figure 3:Shower shapes for different gamma pt bins

Figure 4:Shower shapes for different z-vertex bins