Direct observation of dijets in central Au+Au collisions with STAR
We present first results of azimuthal (Delta phi) correlations of high transverse momentum (p_T) hadrons from the high-statistics Au+Au dataset collected at RHIC in 2004. Previous correlations measurements observed the disappearance of back-to-back (Delta phi ~ pi) correlations in central Au+Au collisions, supporting the emerging picture of parton energy loss in dense QCD matter. In the present analysis, increasing the p_T thresholds reveals a narrow back-to-back dijet peak which emerges above the decreasing combinatoric background. We study the possible medium modification of the dijet fragmentation function and compare to models, to place constraints on the nature and magnitude of in-medium energy loss.
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