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:
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Analysis Note:

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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.