2009.02.06 Pre-shower energy distribution Run6 vs. Run8 geometry

Ilya Selyuzhenkov February 06, 2009

Data sets

  • pp2006 - STAR 2006 pp longitudinal data (~ 3.164 pb^1)
    Trigger: eemc-http-mb-L2gamma [id:137641]
  • mc2006: gamma-jet+QCD jets [p6410EemcGammaFilter] events.
  • Partonic pt range 2-25 GeV.

  • pp2008 - STAR 2008 pp data
    Trigger: etot-mb-l2 [id:7]

Cuts applied

  • Di-jet events
  • Require to reconstruct photon momentum (no gamma-jet isolation cuts)
  • Gamma pt > 7GeV, jet pt > 7GeV
  • L2gamma emulation in Monte-Carlo
  • L2gamma triggered for pp2006 and pp2008 events
  • cos (phi_jet - phi_gamma) < -0.8
  • detector |eta_jet|< 0.8
  • |v_z| < 100


Each figure has:

  • All pre-shower conditions combined, No pre-shower cuts
  • Red circles show pp2006 data
  • Black triangles show pp2008 data
    Data scaled to match the integraled yield from pp2006 data
  • Green line shows MC sum: QCD + gamma-jet
    Monte-Carlo results for QCD and gamma-jet samples are first
    scaled to 3.164 pb^-1 according to Pythia luminosity,
    added together, and then an additional fudge factor of 1.24 applied.
    Fudge factor is defined as pp2006 to Monte-Carlo sum ratio
    for pt_jet>7GeV and pt_gamma>7 candidates


  • Pre-shower energy distributions from pp2008 data set
    are narrower than that for pp2006 data.
    This corresponds to smaller amount of material budget in y2008 STAR geometry.
  • Pre-shower energy distribution from Monte-Carlo with y2006 geometry
    closer follows the distribution from pp2008 data set, rather than that from pp2006 data.
    This indicates the lack of material budget in y2006 Monte-Carlo.

Note: There is a "pre-shower sector 10 problem" for pp2008 data,
which results in migration of small fraction of events with pre-shower>0 into
pre-shower=0 bin (first zero bins in Fig.1 and 2. below).
For pre-shower>0 case this only affects overall normalization of pp2008 data,
but not the shape of pre-shower energy distributions.
I'm running jet-finder+my software to get more statistics from pp2008 data set,
and after more QA will produce list of runs with "pre-shower sector 10 problem",
so to exclude them in the next iteration of my plots.

Figure 1: Pre-shower1 energy distribution

Figure 2: Pre-shower2 energy distribution