10 - H1 - Desy

70 Prompt photon selection
Events
500
400
300
Events
600
a. b.
400
Sum MC
Signal
Background
200
100
200
130
0
140 150 160 170 180
∆Φ
0
0 2 4 6 8 10
p [GeV]
Figure 5.8: The distribution of the ∆Φ (a) and p ⊥ (b) variables. Data points are plotted
together with MC predictions.
5.4 Selection Summary
Table 5.1 summarises all the selection criteria. The inclusive prompt photon selection
requires all selection criteria except the cuts on the accompanying jet. The jet cuts are
applied for the exclusive selection. The selected exclusive sample is divided into direct
and resolved enhanced subsamples based on the x LO
γ cut.
All the cuts were grouped into sets (labeled A-I in the summary table). The table contains
the number of data events and overall signal selection efficiency after various sets of cuts.
One should note that the cut on the inelasticity y is introduced twice, once in the ep
selection section (B) and the second time as a photoproduction selection cut (C). The
first, weaker, cut was introduced for technical reason in order to decrease the amount of
processed data already at the preselection step.
Figure 5.9 presents the signal selection efficiency after various sets of cuts as a function
of the transverse energy and the polar angle of the generated photon. For an efficiency
dependence of E γ T
, the transverse energy generator level cut was skipped in order to
study the behaviour in a broader energy range. One should note the significant drop of
the selection efficiency for low transverse energies already on trigger level (cut set A),
due to the energy treshold of the trigger condition. The trigger efficiency visible in this
plot is lower than discussed in section 4.3.2 (effect particularly visible for high transverse
energies) because low efficiency LAr regions which were already removed in the previous
discussion. Here, LAr calorimeter fiducial cut selection enter on the level of cut set E.
The irregular θ dependence of the cut set A efficiency resembles the zr trigger behaviour
studied previously.
The photon kinematics selection (cut set D) restricts the measurement to the interesting
phase space. The cluster quality criteria (cut set E) cause a significant drop in the
overall selection efficiency but are important for selecting reliable candidates with well
reconstructed properties. The six wheel LAr calorimeter structure is visible in the θ
dependence of the efficiency due to the cuts on LAr z cracks. The hadron suppression
cuts (cut set G) cause an additional 10% efficiency drop, mostly in the forward region