BES v3 paper proposal

Updated on Thu, 2016-02-04 11:42. Originally created by psoren on 2015-05-05 16:26.

Title:
Beam Energy Dependence of the Third Harmonic of Azimuthal Correlations in Au+Au Collisions at RHIC

PA's: Paul Sorensen, Niseem Magdy, Yadav Pandit, Navneet Kumar Pruthi, Hui Wang and Liao Song.

Target Journal: PRL

Updated Analysis Note: https://drupal.star.bnl.gov/STAR/system/files/BES_v3_AnalysisNote_2.pdf

Abstract:

We present results from a harmonic decomposition of two-particle

azimuthal correlations measured in $Au+Au$ collisions for energies

ranging from $\sqrt{s_{NN}}=7.7$ GeV to 200 GeV. The dependence of the

third harmonic $v_3^2\{2\}=\langle cos(\phi_1-\phi_2)\rangle$ is

studied as a function of the longitudinal angle between the particle

pairs $\Delta\eta = \eta_1-\eta_2$. $v_3$ is directly related to the

large $\Delta\eta$ ridge correlations and has been shown in models to

be sensitive to the existence of a low viscosity Quark Gluon Plasma

phase. For sufficiently central collisions, $v_3^2\{2\}$ persist even

down to energies of 7.7 and 11.5 GeV. In peripheral collisions at

these low energies however, no jet-like correlations are observed and

$v_3^2\{2\}$ is consistent with zero. This observation is consistent

with the disappearance of the Quark Gluon Plasma in small systems at

low energies. When scaled by multiplicity, $v_3^2\{2\}$ shows a

minimum near $\sqrt{s_{NN}}=14--20$ GeV, a feature not present in any

current models of heavy-ion collisions.

Figure 1:

Figure 2:

Figure 3:

Figure 4:

Conclusion:

We presented measurements of the collision energy dependence of

\vthree in Au+Au collisions for energies ranging from

$\sqrt{s_{_{NN}}} = $ 7.7 to 200 GeV. Model calculations have shown

that \vthree is particularly sensitive to the presence of a low

viscosity plasma phase in the collision evolution: the smaller scale

geometry fluctuations that lead to \vthree are lost without this phase

while $v_{2}$ can be established over a longer period in a higher

viscosity phase. The conversion of geometry fluctuations in the

initial state have been found to provide a simple explanation for

\vthree and the corresponding ridge structure. By studying the

$\Delta\eta$ dependence of \vthree, we find that for sufficiently

central collisions (\npart $>50$), the ridge and \vthree persists down to

the lowest energies studied. For more peripheral collisions however,

the ridge correlation appears to be entirely abscent for \npart $<50$,

consistent with the disappearance of the Quark Gluon Plasma in small

systems at low energies. When comparing \vthree at RHIC and the LHC,

the much larger multiplicities at the higher energies lead to a much

larger \vthree. When scaled by multiplicity however, $v_3^2\{2\}$

shows a minimum in the range $\sqrt{s_{NN}}=14-20$ GeV. This feature

is not present in any current models of heavy-ion collisions and could

indicate a non-monotonic trend in the pressure of the system. Such a

provacative conclusion however requires a deeper investigation of the

complicated dynamics in that energy range. Such an investigation is

the goal of both major theory and experimental efforts within the

communuity including a second phase of the beam energy scan at RHIC

focusing on collecting larger data samples at energies below 20 GeV.

Supporting material:

https://drupal.star.bnl.gov/STAR/system/files/pwc_preview_topics.pdf

https://drupal.star.bnl.gov/STAR/system/files/sorensen_14.5GeV_update.pdf

https://drupal.star.bnl.gov/STAR/system/files/sorensen_bulkcorr_july16_2014.pdf

https://drupal.star.bnl.gov/STAR/system/files/sorensen_bulkcorr_05_28_2014.pdf

https://drupal.star.bnl.gov/STAR/system/files/sorensen_BES_06_23_2014.pdf

A quote from http://arxiv.org/pdf/1310.1764.pdf relevant to this paper:

"the scaled v3 points over several collision energies and centrality classes form an uniform function of the hydro duration ⟨thydro⟩, whereas for the elliptic flow the relation is distorted by the transport dynamics. Thus, compared to v2, the triangular flow provides a clearer signal for the formation of (near-)ideal fluid in heavy ion collisions."

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BES v3 paper proposal