10 - H1 - Desy

9.5 Comparison to previous measurements 141
20% of the events in the direct enhanced phase space are actually resolved or radiated
events migrating into the high x LO
γ range and contributing significantly to the tails of
both distributions. One possible explanation of the observed discrepancy is actually the
deficit in modelling of the resolved part of the interaction.
9.5 Comparison to previous measurements
The cross sections were calculated in the phase space of the previous measurements allowing
a direct comparison to the published results based on HERA data.
The prompt photon measurement in photoproduction published by the H1 collaboration
[35] was based on HERA I data with an integrated luminosity of 105 pb −1 . The
isolation of the photon is ensured by the cone isolation criteria described in section 8.7.2.
The ZEUS collaboration reported the prompt photon + jet cross section measurement
with 77 pb −1 of HERA I data. Both measurement phase spaces are summarized in the
table 9.1. The H1 results were obtained using a signal-background discriminator based
on three shower shape variables (R T , FLF and HCF - see section 6.1), while results of
the ZEUS collaboration are based on the signal in the Zeus pre-shower detector [131].
The results of both publications were determined using a fitting procedure described in
section 8.6.1.
H1 published phase space
Q 2 < 1 GeV 2
0.2 < y < 0.7
E (η,φ)=1
T
/E γ T < 0.1
5 < E γ T
< 10 GeV
−1.0 < η γ < 0.9
ZEUS published phase space
Q 2 < 1 GeV 2
0.2 < y < 0.8
z > 0.9
7 < E γ T
< 16 GeV
−0.74 < η γ < 1.1
6 < E jet
T
< 17 GeV
−1.6 < η jet < 2.4
Table 9.1: The prompt photon phase space of the H1 [35] and the ZEUS [38] measurements.
For a direct comparison, the phase space of this analysis is adjusted to match the published
ones with the only exception of the photon transverse energy range for the H1 published
phase space and the photon pseudorapidity range for the ZEUS published phase space.
In both cases the difference is preserved in order to visualise the range of the phase space
extension. The differential cross sections in bins of E γ T
in the H1 published phase space
and in bins of η γ in the ZEUS published phase space are presented in figure 9.10.
Figure 9.10a shows the comparison between the published results based on the HERA I
data and the HERA II results of this analysis in the properly adjusted phase space. As
explained in section 4.3, low transverse energies of the photon are not accessible using
H1 HERA II data due to the strong prescaling on the trigger level. Instead, the phase