Speaker
Description
Thermal photon emission from the QGP is visible in the $p_T$ spectrum of direct photons measured in heavy-ion collisions, producing a characteristic exponential dependence of the spectrum at low $p_T$. The ALICE, PHENIX and STAR Collaboration have quantified this inverse slope $T_{eff}$, measuring $\approx 200$-$400$ MeV, close to the range of QGP temperatures seen in hydrodynamic simulations of the plasma.
I will first present a simplified model of heavy-ion collisions in which a well-defined temperature profile of the plasma can be related to the inverse slope of the photon spectrum, providing a connection between the spectrum's inverse slope $T_{eff}$, the QGP's size and maximum temperature, as well as the range of $p_T$ used to determine $T_{eff}$ from the photon spectrum. I will compare these results with existing and new numerical simulations, discussing the role of the plasma's transverse expansion on $T_{eff}$, distinguishing between the initial transverse flow and the radial flow developed from the plasma's expansion.
| Category | Theory |
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