Measurement of the photon–proton total cross section at a center-of-mass energy of 209 GeV at HERA

Abstract

The photon-proton total cross section has been measured in the process e + p → e + γp → e + X with the ZEUS detector at HERA. Events were collected with photon virtuality Q 2 < 0.02 GeV 2 and average γp center-of-mass energy W γp = 209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb −1 . The measured total cross section is σ γp tot = 174±1(stat.)±13(syst.) µb. The energy dependence of the cross section is compatible with parameterizations of high-energy pp and pp data.

Model dependence of theγZdispersion correction to the parity-violating asymmetry in elasticepscattering

“…• Real photoabsorption cross sections have been measured from the pion threshold to very high energies [23][24][25][26][27][28] • Virtual photoabsorption data: high precision data from the JLab E94-110 [29] and the preliminary data from the E00-002 [30] experiments are available in the resonance region; in the DIS region, we quote the data for the DIS structure function F 2 from SLAC NMC Collaboration [31], FNAL E665 collaborations [32] and DESY H1 Collaboration [33].…”

“…Again, some resonance parameters are slightly adjusted to the background, and all changes are quoted in Table II. [23][24][25][26][27][28] (see [36] for the complete list) compared to the two models described in the text. The experimental errors are not shown.…”

Connection of the virtualγ*pcross section ofepdeep inelastic scattering to realγ<

“…The parameters in the Block-Halzen (BH) fit were constrained by requiring that it match smoothly to the very precise fit in the resonance region given by Damashek and Gilman [21]. In the following, we will use the parameters given in BH fit 2; this fits the γp cross section data for W > 2.01 GeV, including the high energy measurements of the H1 [22] and ZEUS [23] groups at HERA at W = 200 and 209 GeV, with a fit probability of 0.88:…”

High Energy Astroparticle Physics at Ooty and the GRAPES-3 Experiment

“…It is well known that in showers initiated by the cosmic ray nuclei the dominant source of the muons, is decays of the charged mesons produced in the hadronic interactions. However, the γ-ray induced showers being electromagnetic in nature, the cross section for the photo-production of the mesons is much smaller than the pair production, by a large factor of ~ 1000 [101,102]. As a consequence, we expect a very tiny fraction of the secondary hadrons to be present in the γ-ray induced showers relative to the proton induced showers.…”

“…[104][105][106]. However, the possibility of such an anomalously high cross section for the photoproduction of the pions is already ruled out by the H1 [101] and the ZEUS [102] experiments on the electron-proton collisions at the HERA accelerator up to an equivalent laboratory energy of 20 TeV. The pion photo-production cross sections used in the Monte Carlo simulations mentioned above, were based on the HERA measurements and at higher energies they were obtained by a smooth extrapolation of the HERA results.…”