Measurements of longitudinal and transverse momentum distributions for neutral pions in the forward-rapidity region with the LHCf detector

TL;DR

This paper reports measurements of neutral pion momentum distributions in the forward region at the LHC, providing data that tests scaling hypotheses and reveals nuclear effects in proton-lead collisions, serving as benchmarks for cosmic ray simulations.

Contribution

It presents the first detailed measurements of neutral pion distributions in the forward region at multiple energies, highlighting nuclear suppression effects and benchmarking hadronic interaction models.

Findings

Compatibility with limiting fragmentation and Feynman scaling in proton-proton collisions.

Observation of significant neutral pion suppression in proton-lead collisions.

Provision of data for improving cosmic ray air shower simulations.

Abstract

The differential cross sections for inclusive neutral pions as a function of transverse and longitudinal momentum in the very forward rapidity region have been measured at the Large Hadron Collider (LHC) with the Large Hadron Collider forward detector (LHCf) in proton-proton collisions at $\sqrt{s}=$ 2.76 and 7 TeV and in proton-lead collisions at nucleon-nucleon center-of-mass energies of $\sqrt{s_\text{NN}}=$ 5.02 TeV. Such differential cross sections in proton-proton collisions are compatible with the hypotheses of limiting fragmentation and Feynman scaling. Comparing proton-proton with proton-lead collisions, we find a sizable suppression of the production of neutral pions in the differential cross sections after subtraction of ultra-peripheral proton-lead collisions. This suppression corresponds to the nuclear modification factor value of about 0.1-0.3. The experimental measurements presented in this paper provide a benchmark for the hadronic interaction Monte Carlo simulation codes that are used for the simulation of cosmic ray air showers.