Measurement of zero degree inclusive photon energy spectra for $\sqrt{s}=$ 900 GeV proton-proton collisions at LHC

TL;DR

This paper reports measurements of inclusive photon energy spectra in very forward proton-proton collisions at 900 GeV at the LHC, comparing results with various hadronic interaction models to evaluate their accuracy.

Contribution

First measurement of forward photon spectra at 900 GeV at the LHC, providing data to test and improve hadronic interaction models used in cosmic-ray physics.

Findings

EPOS 1.99 and SIBYLL 2.1 models agree reasonably with spectral shape

Most models underestimate the cross-section above 300 GeV

Models show similar discrepancies at 7 TeV and 900 GeV energies

Abstract

The inclusive photon energy spectra measured by the Large Hadron Collider forward (LHCf) experiment in the very forward region of LHC proton-proton collisions at $\sqrt{s}=$ 900 GeV are reported. The results from the analysis of 0.30 $\mathrm{nb^{-1}}$ of data collected in May 2010 in the two pseudorapidity regions of $\eta > 10.15$ and $8.77 < \eta < 9.46$ are compared with the predictions of the hadronic interaction models DPMJET 3.04, EPOS 1.99, PYTHIA 8.145, QGSJET I -.1em I-03 and SIBYLL 2.1, which are widely used in ultra-high-energy cosmic-ray experiments. EPOS 1.99 and SYBILL 2.1 show a reasonable agreement with the spectral shape of the experimental data, whereas they predict lower cross-sections than the data. The other models, DPMJET 3.04, QGSJET I -.1em I-03 and PYTHIA 8.145, are in good agreement with the data below 300 GeV but predict harder energy spectra than the data above 300 GeV. The results of these comparisons exhibited features similar to those for the previously reported data for $\sqrt{s}=$ 7 TeV collisions.