Measurement of energy flow, cross section and average inelasticity of forward neutrons produced in $$ \sqrt{s} $$ = 13 TeV proton-proton collisions with the LHCf Arm2 detector

Abstract

In this paper, we report the measurement of the energy flow, the cross section and the average inelasticity of forward neutrons (+ antineutrons) produced in √ s = 13 TeV proton-proton collisions. These quantities are obtained from the inclusive differential production cross section, measured using the LHCf Arm2 detector at the CERN Large Hadron Collider. The measurements are performed in six pseudorapidity regions: three of them (η > 10.75, 8.99 < η < 9.21 and 8.80 < η < 8.99), albeit with smaller acceptance and larger uncertainties, were already published in a previous work, whereas the remaining three (10.06 < η < 10.75, 9.65 < η < 10.06 and 8.65 < η < 8.80) are presented here for the first time. The analysis was carried out using a data set acquired in June 2015 with a corresponding integrated luminosity of 0.194 nb −1. Comparing the experimental measurements with the expectations of several hadronic interaction models used to simulate cosmic ray air showers, none of these generators resulted to have a satisfactory agreement in all the phase space selected for the analysis. The inclusive differential production cross section for η > 10.75 is not reproduced by any model, whereas the results still indicate a significant but less serious deviation at lower pseudorapidities. Depending on the pseudorapidity region, the generators showing the best overall agreement with data are either SIBYLL 2.3 or EPOS-LHC. Furthermore, apart from the most forward region, the derived energy flow and cross section distributions are best reproduced by EPOS-LHC. Finally, even if none of the models describe the elasticity distribution in a satisfactory way, the extracted average inelasticity is consistent with the QGSJET II-04 value, while most of the other generators give values that lie just outside the experimental uncertainties.

The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider

“…The LHCf experiment has measured forward neutron spectra in p-p collisions at 7 and 13 TeV. While the actual inelasticity remains a more theoretical concept not directly accessible by measurements, an analysis based on the forward neutrons can be performed (Adriani et al 2020) exploiting the fact that the forward neutron is often the most energetic particle, and subsequently the inelasticity is the complement of the energy fraction carried by the neutrons. The inelasticity as a conceptual parameter has a large impact on the depth of shower maximum X max , while the number of produced muons in the shower depends only weakly on it.…”

The Muon Puzzle in air showers and its connection to the LHC

“…It is difficult to measure, because the most energetic particle has a small angle to the beam and usually escapes detection. It can be measured with zero-degree calorimeters and has been constrained in pp collisions with very-forward neutrons by LHCf [28]. Also important for the elasticity are the cross-sections for single-and double- and in unbiased p-O collisions at 10 TeV (bottom).…”

The Forward Physics Facility: Sites, Experiments, and Physics Potential

“…As we have seen, the FPF experiments will provide complementary data on far-forward hadron production. While the LHCf experiment has previously measured the neutral pion and neutron production cross sections [322,323,359,360], the FPF experiments can make complementary The vertical axis shows the number of neutrinos per energy bin that go through the detector's cross-sectional area for an integrated luminosity of 3 ab −1 . The different production modes are indicated by different colors: pion decays (red), kaon decays (orange), hyperon decays (magenta), and charm decays (blue).…”