Year: 2026
Type: preprint
Abstract: We report the measurement of direct virtual photon ($γ^*_\text{dir} \rightarrow e^+e^-$) in four Au+Au collision energies at $\sqrt{s_\text{NN}}$ = 14.6--54.4 GeV. The $γ^*_\text{dir}$ yields scale with charged-particle multiplicity ($(dN_{\mathrm{ch}}/dη)^α$) as $α=1.43 \pm 0.04 \text{(stat.)} \pm 0.03\text{(sys.)}$, independent of collision energies and centralities, exceeding hadronic expectations and indicating notable contribution from QGP phase. At $\sqrt{s_{\rm NN}}=$ 54.4 GeV, the direct virtual photon mass distributions are further studied over $0.1 < M_{ee} < 1.1$ GeV/$c^2$, and are found to evolve from exponential to power-law form with increasing $p_\text{T}$, signaling a shift from "blackbody" radiation to emission governed by Kroll-Wada formalism.
Source: arXiv (Cornell University)
Author: STAR Collaboration
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, National Energy Research Scientific Computing Center, Ministry of Education, Culture, Sports, Science and Technology, National Natural Science Foundation of China, Grantová Agentura České Republiky, Bundesministerium für Bildung und Forschung, National Research Foundation of Korea, Emberi Eroforrások Minisztériuma, Agencia Nacional de Investigación y Desarrollo, National Science and Technology Council, Office of Science, Japan Society for the Promotion of Science, National Research, Development and Innovation Office, Nuclear Physics, Lawrence Berkeley National Laboratory
OpenAlex ID: W7222053514