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star physics results: High-pT phenomena

Note: Click on a figure for a larger version.


Figure. (a) The ratio of hadron production in d+Au and Au+Au to p+p collisions as a function of pT. (b) The azimuthal angular correlation of pairs of high pT hadrons in p+p, d+Au, and central Au+Au collisions.

Evidence from d+Au measurements for final-state suppression of high pT hadrons in Au+Au collisions at RHIC

The factor of five suppression of high pT hadron production and the suppression of away-side jets in central Au+Au collisions compared to proton+proton collisions are some of the most exciting results produced by STAR. The interpretation of these effects as due to final-state interactions of jets in the dense matter formed in the collision requires the demonstration that such effects do not occur in high energy nuclear collisions in which no medium is formed. The d+Au collisions from RHIC Run-III provide such a testing ground.

The top panel of the figure shows the ratio of hadron production in d+Au and Au+Au collisions to that in p+p collisions, scaled to account for the nuclear geometry, as a function of pT. High pT hadron production is enhanced in d+Au collisions (R_AB>1), similar to the Cronin enhancement observed in experiments at lower energies, in contrast to the results from Au+Au collisions where only 20% of the expected hadrons are observed.

The lower panel shows the azimuthal angular correlation of pairs of high transverse momentum particles in p+p, d+Au and central Au+Au collision. The peaks seen at small angular separation are characteristic of jet production, while those seen at 180 degrees in p+p and d+Au are characteristic of di-jets. The absence of the second peak in Au+Au collisions demonstrates that the second jet has been absorbed by the medium created in the collisions. These pieces taken together provide strong evidence that the density of the medium generated in central Au+Au collisions is many times that of cold nuclear matter.

Related STAR papers

Evidence from d+Au measurements for final-state suppression of high pT hadrons in Au+Au collisions at RHIC
Phys. Rev. Lett. 91 (2003) 072304
e-Print Archives (nucl-ex/0306024): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

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

Disappearance of back-to-back high pT hadron correlations in central Au + Au collisions at sqrt(snn) = 200 GeV
Phys. Rev. Lett. 90 (2003) 082302
e-Print Archives (nucl-ex/0210033): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server


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