10 - H1 - Desy

64 Prompt photon selection
the remaining DIS background a cut on high inelasticity is introduced. Extremely forward
events which are predominantly due to the interaction of the proton with beam gas are
removed with the cut on low values of inelasticity. In this analysis y is restricted to
0.1 < y < 0.7 range.
The y distribution for selected photon candidates is plotted in fig 5.1a. The data is plotted
together with the sum of MC prediction (scaled to the measured cross section), MC signal,
MC photoproduction background and MC DIS background. The vertical lines indicate
the cut values. The remaining DIS background is estimated to be roughly 2% and its
y dependence is plotted in fig 5.1b. The final results are corrected for its presence by
subtracting the expected contamination.
Events
700
600
500
400
300
200
100
a. b.
Sum MC
Signal
Background
DIS
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
y
DIS contribution [%]
14
12
10
8
6
4
2
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
y
Figure 5.1: Inelasticity estimator y distribution (a) and the estimated DIS events fraction
(b).
5.2 Photon selection
Photons are commonly identified in high energy experiments as compact electromagnetic
clusters without track pointing to it. A similar approach has been taken in this work with
details discussed below.
All LAr calorimeter clusters with transverse energy
and in the pseudorapidity range
5.7 < E γ T
< 17 GeV (5.2)
− 1.1 < η γ < 2.5 (5.3)
are used to define the entry point for photon candidate selection. The pseudorapidity
range covers almost the whole LAr calorimeter acceptance.
5.2.1 Cluster criteria
Clusters close to LAr calorimeter φ and z cracks might possibly suffer from significant
energy leakage. Therefore all the clusters with more than 95% of the energy deposited in