10 - H1 - Desy

26 Theoretical framework
Figure 1.21: Photon production cross sections measured in hadronic collisions compared
to NLO calculations. The E706 data is scaled by factor 10 −4 . The figure taken from [44].
photon measurements are also sensitive to the parton density functions (PDFs) of both
the proton and the photon and may be used in dedicated analyses to fine tune their
parameters. In order to enhance the sensitivity to the parton density functions, the
measurement is performed in bins of x LO
γ
x LO
p
x LO
γ
= E γ T
= E γ T
and x LO
p
defined as
exp(η γ ) + exp(η jet )
,
2E p
(1.40)
exp(−η γ ) + exp(−η jet )
,
2yE e
(1.41)
where E p and E e are the energies of the incoming proton and electron respectively. Both