# Measurements of v2, v3 in p+Au, d+Au and 3He+Au collisions at ­200 GeV from STAR collaboration

Title: Measurements of v2, v3 in central p+Au, d+Au and 3He+Au collisions at ­200 GeV from STAR collaboration

PA: Shengli Huang, Zhenyu Chen, Jiangyong Jia, Roy Lacey, Pengfei Liu, Maowu Nie, Yuri Sato, Chunjian Zhang

Target Journal: Physical Review Letter

Paper Draft:
Draft for PWGC review
drupal.star.bnl.gov/STAR/system/files/starsmallshort_5.pdf

Draft for PWG review:
drupal.star.bnl.gov/STAR/system/files/starsmallshort-6_0.pdf

Analysis Note:

PWGC review
presentation:
drupal.star.bnl.gov/STAR/blog/slhuang/small-system-pwgc-review-request

Abstract:

In this paper, the flow coefficients \$v_2\$ and \$v_3\$ are extracted by four kinds of subtraction methods from long-range two-particle azimuthal angular correlations with \$|\Deta|>\$1.0, as a function of transversal momentum in central p/d/\$^3\$He+Au collisions at \$\sqrtsNN\$ = 200 GeV. At comparable centralities, a universal scaling has been found for \$v_3\$ from \$p\$/\$d\$/\$^3\$He+Au collisions at RHIC to those in \$p\$+Pb at the LHC. Comparing with several hydro-calculations with different assumptions on the initial conditions indicates the initial geometry in small system may be dominated by sub-nucleon fluctuations, while the window is still open for contributions from initial momentum anisotropy and pre-equilibrium dynamics.

Fig.1:Two-particle per-trigger yield distributions for \$^3\$He/\$d\$/\$p\$+Au and \pp collisions at \$\sqrtsNN\$ = 200 as indicated; the trigger and associated particles are both selected from the range \$0.2 <p_{T}< 2.0\$~GeV/c. An illustration of the template fitting procedure are also shown, which employs the MB \pp correlator to estimate the non-flow contributions and to extract the \$v_2\$ and \$v_3\$ flow coefficients.

Fig.2:The \$v_2\$ and \$v_3\$ before and after subtraction in 0\%-2\% \$p\$+Au, 0\%-10\% \$d\$+Au and \$^{3}\$He+Au collisions. Four kinds of subtraction methods have been employed and the detail can be found in text.

Fig.3:Comparing with \$v_2\$ and \$v_3\$ in \$p\$/\$d\$/\$^{3}\$He+Au collisions at 200 GeV from RHIC with that measured in \$p\$+Pb at 5.02 TeV from the LHC. A universal scaling has been found for \$v_3\$ from RHIC to LHC.

Fig.4:Comparison of \$v_2\$ and \$v_3\$ measured central \pau, \dau and \heau collisions with calculations from several hydrodynamical models. Sonic model with initial geometry eccentricity from Nucleon Glauber has been found under-predict \$v_3\$ in all systems. By including the “pre-flow”,  supersonic model can match the \$v_2\$ and \$v_3\$ better.  IP-Glasma+Hydro that includes sub-nucleonic fluctuations + initial momentum correlation over predicts \$v_2\$ but reproduces \$v_3\$ well.