10 - H1 - Desy

7.4 Event class ratios 91
γ
/ E T
HFS
E T
a. b.
1.2 Data
before calibration
MC
/ E T
γ
HFS
E T
1.2 Data
after calibration
MC
1
1
0.8
6 8 10 12 14 16 18 20
γ
[GeV]
E T
0.8
6 8 10 12 14 16 18 20
γ
[GeV]
E T
γ
/ E T
HFS
E T
c. d.
1.2 Data
before calibration
MC
/ E T
γ
HFS
E T
1.2 Data
after calibration
MC
1
1
0.8
-1 -0.5 0 0.5 1 1.5 2
γ
η
0.8
-1 -0.5 0 0.5 1 1.5 2
γ
η
Figure 7.6: The ratio of transverse energy of the hadronic final state to transverse energy
of prompt photon candidate as a function of transverse energy of photon candidate E γ T
(a, b) and its pseudorapidity η γ (c, d). Plots show situation before (a, c) and after (b, d)
hadronic energy calibration.
7.4 Event class ratios
The ratio of direct to resolved cross section in MC is tuned to the measurement. In this
section, a double-step method of tuning that ratio to data is explained. The ratio of direct
to resolved events scale is important due to difference in the selection efficiency between
the two samples, being on average equal to 0.34 for a direct prompt photon signal and
0.27 for a resolved prompt photon signal. Since the efficiency correction is taken purely
from MC, a proper sample mix is required. For the purpose of the event class ratio
determination, the distributions of x jet
γ observable is used. Its definition being similar to
the x LO
γ given by equation 1.41 is an another estimator of the x γ variable, but since it is
using two leading jets, is valid as well for background events:
x jet
γ
= Ejet1 T
exp(−η jet1 ) + E jet2
T
exp(−η jet2 )
, (7.5)
2yE e
with E jet
T
and η jet being the transverse energy and pseudorapidity of the two leading jets,
E e is the energy of the electron beam and y is the inelasticity estimator. For prompt
photon events one of the jets is the photon jet.
• Tuning background event class ratios
The background scales are studied using the low isolated photons (with the isolation