Speaker
Krzysztof Nowak
(Zuerich University)
Description
Prompt-photon cross sections in deep inelastic ep scattering were
measured with the ZEUS detector at HERA using an integrated luminosity
of 320 pb-1. A clear signal for isolated photons in the photon
transverse-energy and rapidity ranges 4 < E_T^gamma < 15 GeV and
-0.7 < eta^gamma < 0.9 was observed for virtualities of the
exchanged photon of Q^2 > 10 GeV^2. Measurements of differential cross
sections are presented for inclusive prompt-photon production as a
function of Q^2, x_Bj, E_T^gamma and eta^gamma. Perturbative QCD
predictions are compared to the measurements.
The production of isolated photons in deep-inelastic scattering
$ep\to e \gamma X$ is measured with the H1 detector at HERA. The measurement
is performed in the kinematic range of negative four-momentum transfer
squared 4<Q^2<150 GeV^2 and a mass of the hadronic system W_X>50 GeV. The
analysis is based on a total integrated luminosity of 227 pb^-1. The
production cross section of isolated photons with a transverse energy
in the range 3 < E_T^\gamma < 10 GeV and pseudorapidity range
-1.2 < \eta^\gamma < 1.8 is measured as a function of
E_T^\gamma, \eta^\gamma and Q^2. Isolated photon cross sections are also
measured for events with no jets or at least one hadronic jet.
The measurements are compared with predictions from Monte Carlo generators
modelling the photon radiation from the quark and the electron lines, as
well as with calculations at leading and next to leading order in the strong
coupling. The predictions significantly underestimate the measured cross
sections.
A measurement of the production of prompt photons in photoproduction by
the H1 experiment at HERA is presented. The analysis is based on the data
taken in the years 2004-2007, with a total integrated luminosity of
340 pb^-1. Prompt photon cross sections are measured for photons with a
transverse energy in the range 6 < E_T^gamma < 15 GeV and in the
pseudorapidity range -1 < eta^gamma < 2.4. Cross sections for prompt
photon events with an additional hadronic jet are measured as a function
of the transverse energy and pseudorapidity of the jet and of the momentum
fractions x_gamma and x_proton of the incident photon and proton,
respectively, carried by the constituents participating in the hard scattering
process. Additionally, the transverse correlation between the photon and
the jet is studied. The results are compared with predictions of a
next-to-leading order calculation and a calculation based on the k_T
factorisation approach.
Primary author
Krzysztof Nowak
(Zuerich University)
Co-author
Katja Krueger
(Heidelberg University)
