Why are the dilepton temperatures at the relativistic heavy-ion colliders are constant, T ~ 0.3 GeV?

Abstract

The STAR collaboration at RHIC and the ALICE collaboration at the LHC have reported dielectron spectra in the intermediate mass region, M = (1-3) GeV, which reveal a strikingly constant, energy-independent emission temperature $T_{IMR}\simeq 0.3\text{GeV}$ over a broad range of collision energies, $\sqrt{s_{NN}}=27-5020\text{GeV}$. This unexpected ''thermostat'' behavior raises fundamental questions: why does the temperature remain constant despite increasing collision energy,and what mechanism governs this apparent universality?

5 pages, 1 figure