Measurement of very forward neutron energy spectra for 7 TeV proton--proton collisions at the Large Hadron Collider

TL;DR

This study measures very forward neutron energy spectra in 7 TeV proton-proton collisions at the LHC, providing data to test and improve hadronic interaction models used in cosmic-ray physics.

Contribution

First measurement of neutron energy spectra at very forward angles in 7 TeV proton-proton collisions, comparing results with current hadronic interaction models.

Findings

QGSJET II-03 predicts high neutron production at highest pseudo-rapidity.

DPMJET 3.04 describes lower pseudo-rapidity results well.

No model fully explains the neutron spectra across all pseudo-rapidity ranges.

Abstract

The Large Hadron Collider forward (LHCf) experiment is designed to use the LHC to verify the hadronic-interaction models used in cosmic-ray physics. Forward baryon production is one of the crucial points to understand the development of cosmic-ray showers. We report the neutron-energy spectra for LHC $\sqrt{s}$ = 7 TeV proton--proton collisions with the pseudo-rapidity $\eta$ ranging from 8.81 to 8.99, from 8.99 to 9.22, and from 10.76 to infinity. The measured energy spectra obtained from the two independent calorimeters of Arm1 and Arm2 show the same characteristic feature before unfolding the difference in the detector responses. We unfolded the measured spectra by using the multidimensional unfolding method based on Bayesian theory, and the unfolded spectra were compared with current hadronic-interaction models. The QGSJET II-03 model predicts a high neutron production rate at the highest pseudo-rapidity range similar to our results and the DPMJET 3.04 model describes our results well at the lower pseudo-rapidity ranges. However no model perfectly explains the experimental results in the whole pseudo-rapidity range. The experimental data indicate the most abundant neutron production rate relative to the photon production, which does not agree with predictions of the models.