Authors: P. Bussey, D. Saxon, I. Skillicorn, O. Kuprash, N. Zhmak
Following our earlier paper measuring inclusive cross sections for prompt photons in DIS, we now measure cross sections for prompt photons accompanied by a jet, using the fulll HERA II sample.
Resource material
The main methods used for the photon signal are in Matthew Forrest's thesisPreliminary talk to the QCD group (17.3.11) Postscript to above. There was an error in the comparison with Matthew's inclusive results. The corrected plots are: Q2, ET, eta, x
We request preliminary status for the plots below
The first set of plots all illustrate the fits to the photon signal in terms of the hadronic background (variable), a fixed lepton-radiated photon term (LL) and a variable quark-radiated term(QQ). Fits are performed for data within each bin of each measured variable.
Global fit to fmax eps , pdf
Global fit to dz eps , pdf
Control plot 2 eps , pdf
Fits to dz in bins of ET(gamma) eps , pdf
Fits to dz in bins of eta(gamma) eps , pdf
Fits to dz in bins of ET(jet) eps , pdf
Fits to dz in bins of eta(jet) eps , pdf
Fits to dz in bins of Q2 eps , pdf
Fits to dz in bins of x eps , pdf
A Q2 reweighting formula was applied. Here are the details
The final plots show the cross sections with respect to kinetic variables, compared to the Djangoh/Ariadne calculation of the LL cross section plus the average fitted Pythia QQ cross section including the fitting factor of of 1.6. Quite good agreement is seen.
The most important general event cuts are:10 < Q2 < 350 GeV2 electron angle > 140 deg 4 < ET(gamma) < 15 GeV 2.5 < ET(jet) GeV -0.7 < eta(gamma) < 0.9 -1.5 < eta(jet) < 1.8
together with isolation and cleaning cuts on the photon candidate.
Differential cross sections results
(only pdf files right now)
ET photon eps , pdf
eta photon eps , pdf
ET jet eps , pdf
eta jet eps , pdf
Q2 eps , pdf
X eps , pdf
(Note that the Q2 MC is effectively a check on the reweighting.)