Neutron emission from the photon-induced reactions in ultraperipheral ultrarelativistic heavy-ion collisions

TL;DR

This paper models neutron emission in ultraperipheral heavy-ion collisions at LHC energies, analyzing photon-induced reactions and comparing theoretical approaches to recent ALICE experimental data.

Contribution

It introduces a simple two-component model for photon energy transfer and compares it with existing codes, enhancing understanding of neutron emission mechanisms.

Findings

High photon energies are crucial for small neutron multiplicities.

The model aligns with ALICE data on neutron emission.

Charged particle emission estimates are discussed in context of recent measurements.

Abstract

The ultraperipheral collisions are the source of various interesting phenomena based on photon-induced reactions. We calculate cross sections for single and any number of n, p, $\alpha$, $\gamma$-rays in ultraperipheral heavy-ion collision for LHC energies. We analyze the production of a given number of neutrons relevant for a recent ALICE experiment, for $\sqrt{s_{NN}}$ = 5.02~TeV. In our approach, we include both single and multiple photon exchanges as well as the fact that not all photon energies are used in the process of equilibration of the residual nucleus. We propose a simple two-component model in which only part of photon energy $E_\gamma$ is changed into the excitation energy of the nucleus ($E_{exc} \neq E_{\gamma}$) and compare its results with outcomes of HIPSE and EMPIRE codes. The role of high photon energies for small neutron multiplicities is discussed. Emission of a small number of neutrons at high photon energies seems to be crucial to understand the new ALICE data. All effects work in the desired direction, but the description of the cross section of four- and five-neutron emission cross sections from first principles is rather demanding. The estimated emission of charged particles such as protons, deuterons and $\alpha$ is shortly discussed and confronted with very recent ALICE data, obtained with the proton Zero Degree Calorimeter.