Measurement of Di-jet Cross-Sections in Photoproduction and Photon Structure
To achieve this the H1 experiment has used a sample of photoproduction
events with an explicit di-jet structure. In order to ensure sufficiently
energetic interactions between a quasireal photon and a proton, the electron
was tagged under very small angles and selected to carry roughly half the
energy of the incident lepton beam. At lowest order the two jets originate
from the hard interaction between a parton of the proton and a parton with
momentum fraction xgamma in the photon. Since the partonic content
of the proton has been well measured the partonic content of the photon
can be inferred by an unfolding procedure.
The extraction procedure is severely hampered at small transverse momenta of the jets by the influence of multiple partonic interactions which are not easily included in the theoretical description. However, at larger ET perturbative QCD is able to successfully describe the measured distributions without being dominated by such disturbing influences. H1 has measured the influence of the underlying events and hence could extract the gluonic component in the photon (see figure).
number of gluons in the photon is seen to rise with decreasing xgamma,
an observation that has also been made for the gluon component in the proton.
This feature seems to be a general property of quarkonic matter surrounded
by gluons. The measured distribution is well described by a QCD model (in
leading order perturbation theory).
Last Update Feb 29, 2000, E. Elsen