Spectra and elliptic flow of thermal photons from full overlap U+U collisions at RHIC

TL;DR

This study uses hydrodynamic modeling to compare thermal photon spectra and elliptic flow in different uranium-uranium collision orientations at RHIC, revealing orientation-dependent differences and similarities with gold-gold collisions.

Contribution

It provides the first detailed comparison of thermal photon production and elliptic flow between tip-tip and body-body U+U collisions at RHIC using hydrodynamic simulations.

Findings

Thermal photon production is higher in tip-tip U+U collisions for p_T > 1 GeV.

Body-body U+U collisions produce photon spectra similar to central Au+Au collisions.

Elliptic flow v_2 is large for body-body and near zero for tip-tip U+U collisions.

Abstract

We calculate $p_T$ spectra and elliptic flow for tip-tip and body-body configurations of full overlap uranium-uranium (U+U) collisions using a hydrodynamic model with smooth initial density distribution and compare the results with those obtained from Au+Au collisions at RHIC. Production of thermal photons is seen to be significantly larger for tip-tip collisions compared to body-body collisions of uranium nuclei in the region $p_T >$ 1 GeV. The thermal photon spectrum from body-body collisions is found to be close to the spectrum from most central Au+Au collisions at RHIC. The elliptic flow parameter calculated for body-body collisions is found to be large and comparable to the $v_2(p_T)$ for mid-central collisions of Au nuclei. On the other hand, as expected, the $v_2(p_T)$ is close to zero for tip-tip collisions. The qualitative nature of the photon spectra and elliptic flow for the two different orientations of uranium nuclei is found to be independent of the initial parameters of the model calculation. We show that the photon results from fully overlapping U+U collisions are complementary to the results from Au+Au collisions at RHIC.