2008.05.27 Shower shapes: pp2006 data, MC gamma-jet and QCD jets, gammas from eta

Ilya Selyuzhenkov May 27, 2008

Shower shapes and triple Gaussian fits for gammas from eta-meson

Figure 1: Shower shapes and triple Gaussian fits for photons from eta-meson
sorted by different conditions of EEMC 1st and 2nd pre-shower layers.
Note: All shapes have been normalized at peak to unity


Triple Gaussian fit parameters:
Pre1=0 Pre2=0
Pre1=0 Pre2>0
Pre1>0 Pre2>0


Shower shapes: pp2006, MC gamma-jet and QCD jets, gammas from eta

Shower shapes comparison between different data sets:

  • gammas from eta-meson decay. Obtained from Will's eta-meson analysis
  • pp2006 - STAR 2006 pp longitudinal data (~ 3.164 pb^1) after applying gamma-jet isolation cuts.
  • gamma-jet - data-driven Pythia gamma-jet sample (~170K events). Partonic pt range 5-35 GeV.
  • QCD jets - data-driven Pythia QCD jets sample (~4M events). Partonic pt range 3-65 GeV.

Some observations:

  • Shapes for gammas from eta-meson decay
    are in a good agreement with those from MC gamma-jet sample
    (compare red squares with blue triangle in Fig. 2 and 3).

    MC gamma-jet shapes obtained by running a full gamma-jet reconstruction algorithm,
    and this agreement indicates that we are able to reconstruct gamma shapes
    which we put in with data-driven shower shape library.

  • MC gamma-jet shapes match pp2006 data shapes
    for pre1=0 condition, where we expect to be very efficient in background rejection
    (compare red squares with black circles in upper plots of Fig. 2 and 3).

    This indicates that we are able to reproduce EEMC SMD of direct photons with data-driven Monte-Carlo.

  • There is no match between Monte-Carlo QCD background jets and pp2006 data
    for the case when both pre-shower layer fired (pre1>0 and pre2>0).
    (compare green triangles with black circes in bottom right plots of Fig.2 and 3).
    This is the region where we know background dominates our gamma-jet candidates.

    This shows that we still do not reproduce SMD response for our background events
    in our data-driven Monte-Carlo simulations
    (note, that in Monte-Carlo we replace SMD response with real shapes for all background photons
    the same way we do it for direct gammas).

Figure 2: Shower shapes comparison between different data sets.
Shapes for gamma-jet candidates obtained with the same gamma-jet reconstruction algorithm
for three different data samples (pp2006, gamma-jet and QCD jets MC).
pt cuts of 7GeV for the gamma and of 5 GeV for the away side jet have been applied.


Figure 3:Same as Fig. 2, but with no cuts on gamma and jet pt.
All shapes are similar to those in Fig. 2 with an additional pt cuts.
Note, that blue triangles are the same as in Fig. 2.