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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. |
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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.
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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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