Initial-State Temperature of Light Meson Emission Source From Squared Momentum Transfer Spectra in High-Energy Collisions

The squared momentum transfer spectra of light mesons, π 0 , π + , η , and ρ 0 , 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 (⟨ p T ⟩) 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 ⟨ p T ⟩ and T i , increases with increasing of Q 2 and x B .

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