Abstract
The squared momentum transfer spectra of light mesons, π0, π+, η, and ρ0, produced in high-energy virtual photon-proton (γ*p) → 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 γ* 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 (⟨pT⟩) and the initial-state temperature (Ti) increase from lower squared photon virtuality (Q2) and Bjorken variable (xB) to higher one. This renders that the excitation degree of emission source, which is described by ⟨pT⟩ and Ti, increases with increasing of Q2 and xB.
Highlights
In the evolution process of high-energy nucleus-nucleus collisions, the reaction system undergoes several main stages which are separately the incoming of nuclei, beginning of collisions, strongly-coupled quark-gluon plasma phase or hot-dense matter phase, mixed phase, and hadron gas
Our results show that the average transverse momentum (〈pT〉) and the initial-state temperature (Ti) increase from lower squared photon virtuality (Q2) and Bjorken variable to higher one
Q2 is the absolute value of the squared mass of c* that is exchanged between the scattered electron and the target proton, and it effectively represents the transverse size of the probe [38]
Summary
In the evolution process of high-energy nucleus-nucleus (heavy-ion) collisions, the reaction system undergoes several main stages which are separately the incoming of nuclei, beginning of collisions, strongly-coupled quark-gluon plasma (sQGP) phase or hot-dense matter phase, mixed phase, and hadron gas. The distribution of squared momentum transfer spectra are obtained and used to fit the experimental data for extracting 〈pT〉 and Ti. To describe the equilibrium degree of the system, one can use the Tsallis distribution [23, 24] or Hagedorn function [25] to fit pT spectra directly. The study of transverse momentum spectra of light mesons is very important to explore the reaction mechanism and evolution process of high-energy collisions. The squared momentum transfer spectra of light mesons, π0, π+, η, and ρ0, produced in high-energy c*p collisions measured by the CLAS Collaboration [37,38,39,40] are fitted by the results originating from the Erlang pT distribution with the Monte Carlo method. The CLAS experimental data are measured at different squared photon virtuality Q2 and Bjorken variable xB, where Q2 and xB will be discussed later in the Subsection 2.3
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