Background subtracted 3-particle correlations for (a) pp, (b)d+Au, (c) 80-50% Au+Au, (d) 50-30% Au+Au, (e)30-10% Au+Au, and (f)12% central Au+Au.
star focus: indication of conical emission at RHIC
Highlights from the STAR paper Indications of Conical Emission of Charged Hadrons at RHIC submitted recently to Physical Review Letters.
Posted: Jun 13, 2008

Experimental observation of jet-quenching studies in STAR revealed: on the away side of a high transverse momentum (pt) trigger particle the correlated yield is strongly suppressed at pt > 2 GeV/c while at lower pt the yield is enhanced and the correlated hadrons appear to be partially equilibrated with the bulk medium and are broadly distributed in azimuth.
A number of physics mechanisms may account for the observations: broadened jets due to large angle gluon radiation, deflected jets due to collective radial flow of the bulk or pathlength dependent energy loss, and conical emission due to Cerenkov gluon radiation or Mach-cone shock waves generated by large energy deposition in the hydrodynamic medium. Identifying the underlying mechanism is important as it may probe the medium properties such as its speed of sound and equation of state.
To discriminate between the various mechanisms, we have performed an analysis of 3-particle azimuthal correlations between a high pt trigger particle and two lower pt associated particles. Particle emission on a cone around the away-side jet axis would lead to pairs of correlated hadrons dominantly populating at the cone angle from pi (the away-side of the trigger particle), with equal probability to be far apart (symmetric about pi) and close together.

From an analysis based on a two-component approach we observe the background subtracted 3-particle azimuthal correlations (see figure) for central Au+Au collisions shows additional peaks on the away side along the off-diagonal, indicating large opening angles between the away-side correlated pairs, symmetric about pi. The off-diagonal side peaks are prominent; these peaks are evidence of conical emission of charged hadrons correlated with high pt trigger particles. The side peaks in the diagonal projection contain conical emission and possibly other contributions such as kt broadening, large angle gluon radiation, and deflected jets.

Further details can be found in the following STAR paper -
Indications of Conical Emission of Charged Hadrons at RHIC - arXiv:0805.0622.

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