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star physics results: High-pT phenomena

Note: Click on a figure for a larger version.


Figure. RAB as a function of pT for six centrality classes at sqrt(snn) = 130 GeV.

Centrality dependence of high pT hadron suppression in Au+Au collisions at sqrt(snn) = 130 GeV

The first Au+Au collisions at RHIC were recorded in 2000 at center of mass energy sqrt(snn) = 130 GeV. STAR measured the spectra of charged hadrons as a function of transverse momentum and centrality. These data were compared to a composite reference spectrum of p+p collisions for the same beam energy in order to evaluate nuclear effects on hadron production at high pT. The ratio RAB = (d2NAB/dpT deta) / (TAB d2sigmapp/dpT deta) where d2NAB/dpT deta is the differential yield per event in the nuclear collision A+B, TAB=< Nbinary> sigmappinel describes the nuclear geometry, and d2sigmapp/dpT deta is for p+p inelastic collisions. < Nbinary> is the mean number of binary NN interactions for the given centrality class of A+B collisions. In the absence of nuclear effects such as shadowing, the Cronin effect, or gluon saturation, hard process rates are expected to scale with < Nbinary> and RAB=1.

However, STAR observed that at the highest pT, hadron suppression of approximately a factor 4-5 is observed for the most central collisions: inclusive hadron production is strongly suppressed at high pT in central Au+Au collisions. For the most peripheral collisions RAB is consistent with unity, while intermediate centralities interpolate smoothly between the extremes.

These data are consistent with a scenario in which jets produced early in the collision interact strongly with the medium, reducing the yields of "leading" charged hadrons compared to the yields from p+p collisions, where no medium is present.

Related STAR papers
Centrality Dependence of High pT Hadron Suppression in Au + Au Collisions at sqrt(snn) = 130 GeV
Phys. Rev. Lett. 89 (2002) 202301
e-Print Archives (nucl-ex/0206011): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

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