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star physics results: Event-wise observables

Note: Click on a figure for a larger version.


Figure. The minimum-bias values of v2, v4, and v6 with respect to the second harmonic event plane as a function of transverse momentum. The v2 values have been divided by a factor of two to fit on scale. Also shown are the three-particle cumulant values (triangles) for v4 (v4{3}). The dashed curves are 1.2 v22 and 1.2 v23

Higher Harmonics of the Azimuthal Anisotropy

This is the first measurement of higher harmonics of the momentum anisotropy at RHIC, and it is expected that these higher harmonics will be a sensitive test of the initial configuration of the system, since they provide a Fourier analysis of the shape in momentum space which can be related back to the initial shape in position space.

The results as a function of transverse momentum are shown in the figure for minimum bias collisions (0 - 80% centrality). Shown for v4 are both the analysis relative to the second harmonic event plane, v4{EP2}, and the three-particle cumulant, v4{3}. Both methods determine the sign of v4 to be positive. As a function of pt, v4 rises more slowly from the origin than v2, but does flatten out at high pt like v2. The v6(pt) values are consistent with zero.

It has proposed that for the higher harmonics, vn might be proportional to v2n/2. In order to test the applicability of this scaling, we have also plotted v22 and v23 in the figure as dashed lines. The proportionality constant has been taken to be 1.2 in order to fit the v4 data. The fit is good, and v6, although essentially zero, is not inconsistent with scaling as v23.

Related STAR papers
Azimuthal anisotropy at the Relativistic Heavy Ion Collider: the first and fourth harmonics
Phys. Rev. Lett. 92 (2004) 062301
e-Print Archives (nucl-ex/0310029): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

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