# Quark Matter 2018

13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

## Effect of initial state on thermal photons in heavy ion collisions

15 May 2018, 17:00
2h 40m
First floor and third floor (Palazzo del Casinò)

### First floor and third floor

#### Palazzo del Casinò

Poster Electromagnetic and weak probes

### Speaker

Mr Pingal Dasgupta (Variable Energy Cyclotron Centre)

### Description

The experimental measurement of the direct photon $v_2$ and the theoretical prediction for the same differ by a large margin both at RHIC and at the LHC energies. This is known as the direct photon puzzle". We investigate the effect of initial conditions on the production and elliptic flow of photons from relativistic heavy ion collisions in detail.

It is well known that the inclusion of fluctuations in the hydrodynamic initial condition explains the experimental data on hadronic spectra and elliptic flow better compared to a smooth initial condition and it also increases the production and $v_2$ of photons significantly. In the same spirit, we consider another realistic constraint; initial state nucleon shadowing in the Monte-Carlo Glauber model and investigate the effect of shadowed initial condition on the production and elliptic flow of thermal photons at RHIC and LHC collision conditions [1].

In addition, we calculated the $p_T$ spectra and elliptic flow of thermal photons for two different orientations of fully overlapping uranium nuclei at 193A GeV at RHIC using a hydrodynamic model [2]. We see that the elliptic flow from body-body collisions of uranium nuclei is large and comparable to the photon $v_2$ obtained from mid-central collisions of gold nuclei at 200A GeV. We show that the photon results from fully overlapping U+U collisions are complementary to the results from Au+Au collisions at RHIC.

[1] P.~Dasgupta, R.~Chatterjee, S.~K.~Singh and J.~E.~Alam, arXiv:1704.05715.
[2] P.~Dasgupta, R.~Chatterjee and D.~K.~Srivastava, Phys.\ Rev.\ C {\bf 95}, no. 6, 064907 (2017).

Centralised submission by Collaboration Presenter name already specified Theory

### Primary author

Mr Pingal Dasgupta (Variable Energy Cyclotron Centre)

### Co-authors

Dinesh Srivastava (VECC) Prof. Jan-e Alam (Variable Energy Cyclotron Centre) Mr Sushant K. Singh (Variable Energy Cyclotron Centre)