Rotating Synchrotron Radiation (RoSyRa): photon emission from magnetized and rotating quark-gluon plasma

Abstract

This paper investigates the production of non-prompt photons originating from rotating synchrotron radiation (RoSyRa), specifically the emission of photons by a rigidly rotating quark-gluon plasma in thermal equilibrium, in the presence of an external magnetic field. We compute the non-prompt photon spectrum and its elliptic flow ($v_2$) at mid-rapidity. In particular, we investigate the finite volume effects. We find that at low transverse momentum, the magnetic field induces a significant $v_2$, while the plasma rotation boosts the synchrotron radiation of negatively charged quarks. These effects account for both the observed excess of direct photons and their elliptic flow, contributing to the resolution of the "direct photon puzzle".

Figures (17)

• Figure 1: Top: photon spectrum, bottom: elliptic flow $v_2$, for $eB=18000$ MeV$^2$, $\Omega=2$ MeV, $T=200$ MeV, $R=5$ fm, two quark flavors, the cylinder height is $L=10$ fm and the QGP lifetime $c\Delta t = 10$ fm. The data is adapted from PHENIX_yields_2014PHENIX_yields_2022PHENIX_v2_2012PHENIX_v2_2016, the multi-messengers predictions are given in Gale:2021emg.
• Figure 2: Photon spectrum, for $eB=18000$ MeV$^2$, $\Omega=3$ MeV, $T=300$ MeV, $R=10$ fm, $L=10$ fm $\Delta t =10$ fm/c and two flavors. The data is adapted from PHENIX_yields_2014PHENIX_yields_2022. The cyan line with triangles: $\Omega=0$. The dark violet line with circles: $\Omega\neq 0$ (RoSyRa).
• Figure 3: The rapidity-azimuthal $(y-\phi)$ hyperbolic coordinate system compared with the cylindrical coordinates. A generic vector $\bm{k}$, e.g. the photon momentum, is decomposed into a transverse (to the beam) $k_T$ and longitudinal component $k_z$; its component along the magnetic field $\bm{B}$ is $k_y$, and $k_\perp$ is its component perpendicular to $\bm{B}$.
• Figure 4: The numerical results for the integrated rates (\ref{['eq:RIntegral']}) and the elliptic flow (\ref{['eq:v2Integral']}) in comparison with Wang:2020dsr.
• Figure 5: Non-rotating plasma: thermodynamic limit $R=\infty$ of rates as a function of $\theta$ for various values of photon transverse momenta $k_T$.