Relativistic nuclear collisions as seen through photons

by Jean-Francois Paquet (Vanderbilt University)

Monday Sep 7, 2026, 4:00 PM → 6:00 PM Europe/Zurich

4/2-037 - TH meeting room (CERN)

The $p_T$ spectrum of photons is well understood in relativistic collisions of both protons and of heavy ions, as long as the photon $p_T$ exceeds 5-10 GeV. For lower-$p_T$ photons, the spectrum differs qualitatively between proton and heavy-ion collisions. In the heavy-ion case, the production of photons at $p_T$ below a few GeV appears to be dominated by thermal radiation from quark-gluon plasma. I will discuss the status of theoretical calculations of the photon $p_T$ spectrum in nuclear collisions, reviewing the current agreement with experimental data. I will present new results on the interpretation of the inverse slope ("effective temperature") of the photon spectrum, including (i) a revised picture of the effect of Doppler blue-shifts, (ii) a connection to the maximum temperature of the plasma, and (iii) important practical caveats related to the impact of non-thermal photon sources.