Spectra and elliptic flow of thermal photons from full-overlap U+U collisions at energies available at the BNL Relativistic Heavy Ion Collider

We calculate $p_T$ spectra and elliptic flow for tip-tip and body-body configurations of full-overlap uranium-uranium $\left(\text{U}+\text{U}\right)$ collisions by using a hydrodynamic model with smooth initial density distribution and compare the results with those obtained from $\text{Au}+\text{Au}$ collisions at the BNL Relativistic Heavy Ion Collider (RHIC). Production of thermal photons is seen to be significantly larger for tip-tip collisions compared with body-body collisions of uranium nuclei in the region $p_T>1$ GeV. The difference in the results for the two configurations of $\text{U}+\text{U}$ collisions depends on the initial energy deposition which is yet to be constrained precisely from hadronic measurements. The thermal photon spectrum from body-body collisions is found to be close to the spectrum from most-central $\text{Au}+\text{Au}$ collisions at RHIC. The elliptic-flow parameter calculated for body-body collisions is found to be large and comparable to the $v_2\left(p_T\right)$ for mid-central collisions of Au nuclei. On the other hand, as expected, $v_2\left(p_T\right)$ 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 $\text{U}+\text{U}$ collisions are complementary to the results from $\text{Au}+\text{Au}$ collisions at RHIC.

Figure 1

Schematic of tip-tip and body-body collision of full-overlap uranium nuclei.

Figure 2

Time evolution of (a) average temperature $\langle T\rangle$ and (b) average transverse flow velocity $\langle v_T\rangle$ for tip-tip and body-body full-overlap $\text{U}+\text{U}$ collisions at RHIC.

Figure 3

Thermal photon (a) $p_T$ spectra and (b) elliptic flow from full-overlap $\text{U}+\text{U}$ collisions using hydrodynamic model for ${\tau }_0=0.6\mathrm{fm}$ and $\alpha =0.25$.

Figure 4

Thermal photon (a) $p_T$ spectra and (b) elliptic flow from full-overlap $\text{U}+\text{U}$ collisions using the hydrodynamic model for ${\tau }_0=0.2\mathrm{fm}$ and $\alpha =0.25$.

Figure 5

Thermal photon (a) $p_T$ spectra and (b) elliptic flow from full-overlap $\text{U}+\text{U}$ collisions using hydrodynamic model for ${\tau }_0=0.6\mathrm{fm}$ and $\alpha =0$.

Figure 6

Direct photon (thermal and prompt) spectra from full-overlap $\text{U}+\text{U}$ collisions.