Initial-state temperature of light meson emission source from squared momentum transfer spectra in high-energy collisions

TL;DR

This study analyzes the squared momentum transfer spectra of light mesons in high-energy electron-proton collisions, revealing that the initial-state temperature and transverse momentum increase with higher photon virtuality and Bjorken variable, indicating greater excitation of the emission source.

Contribution

The paper introduces a thermal model using Erlang distribution to describe meson transverse momentum spectra and links initial-state temperature to collision parameters, providing new insights into emission source excitation.

Findings

Initial-state temperature increases with $Q^2$ and $x_B$.

Average transverse momentum rises with higher virtuality and Bjorken variable.

Emission source excitation degree correlates with collision parameters.

Abstract

The squared momentum transfer spectra of light mesons, $\pi^0$, $\pi^+$, $\eta$, and $\rho^0$, produced in high-energy virtual photon-proton ($\gamma^{*} p$) $\rightarrow {\rm meson + nucleon}$ process in electron-proton ($ep$) collisions measured by the CLAS Collaboration are analyzed by the Monte Carlo calculations, where the transfer undergoes from the incident $\gamma^*$ to emitted meson or equivalently from the target proton to emitted nucleon. In the calculations, the Erlang distribution from a multi-source thermal model is used to describe the transverse momentum spectra of emitted particles. Our results show that the average transverse momentum ($\langle p_T\rangle$) and the initial-state temperature ($T_i$) increase from lower squared photon virtuality ($Q^2$) and Bjorken variable ($x_B$) to higher one. This renders that the excitation degree of emission source, which is described by $\langle p_T\rangle$ and $T_i$, increases with increasing of $Q^2$ and $x_B$.