# Quark Matter 2019 - the XXVIIIth International Conference on Ultra-relativistic Nucleus-Nucleus Collisions

3-9 November 2019
Wanda Reign Wuhan Hotel
Asia/Shanghai timezone

## Measurement of path length-dependent $v_1$ of high-$p_{\mathrm{T}}$ charged hadrons in Au+Au collisions by the STAR experiment

4 Nov 2019, 17:40
20m
Wanda Han Show Theatre & Wanda Reign Wuhan Hotel

#### Wanda Han Show Theatre & Wanda Reign Wuhan Hotel

Poster Presentation Initial state and approach to equilibrium

### Speaker

Sooraj Krishnan Radhakrishnan (Lawrence Berkeley National Laboratory)

### Description

In heavy-ion collisions, the thermalized matter is tilted in the reaction plane as a function of rapidity, while the production profile of partons from hard scatterings is symmetric in rapidity [1]. This leads to a rapidity-odd asymmetry in the medium path length traversed by the hard partons and results in a rapidity-odd directed flow ($v_1$). Measurements of high-$p_{\mathrm{T}}$ hadron $v_1$ can provide valuable constraints on the initial longitudinal distribution of the fireball as well as the path length-dependent momentum loss of the partons. A similar effect, producing significantly large directed flow for heavy flavor mesons, was predicted [2] and has been observed for $D^0$ mesons (at 3$\sigma$ significance) by STAR recently.

In this poster, we will present the first measurement of pseudorapidity and centrality dependence of the $v_1$ of high-$p_{\mathrm{T}}$ ($>$ 5 GeV/c) charged hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 and 200 GeV. The $v_1$ of charged hadrons is found to change sign twice as a function of $p_{\mathrm{T}}$ and show large negative slope at high-$p_{\mathrm{T}}$, similarly to $D^0$ mesons. The measurements will be compared to different model calculations and the sensitivity to different initial density distributions will be discussed.

[1] P. Bozek, I. Wyskiel, Phys. Rev. C. 81 (2010) 054902; A. Adil, M. Gyulassy, Phys. Rev. C. 72 (2005) 034907.
[2] S. Chatterjee, P.Bozek, Phys. Rev. Lett. 120 (2018) 192301.

### Primary author

Sooraj Krishnan Radhakrishnan (Lawrence Berkeley National Laboratory)