High pT physics in PHENIX at RHIC

by M.J.Tannenbaum (Brookhaven National Laboratory)

Monday 11 Jun 2001, 11:00 → 12:00 Europe/Zurich

160-1-1-009 (CERN)

Hard scattering in p-p collisions was discovered at the CERN ISR by the observation of a very large flux of high transverse momentum pions with a power-law tail which varied systematically with the c.m. energy of the collision. This observation in 1972 proved that the partons of deeply inelastic scattering were strongly interacting. Further ISR measurements utilizing inclusive single or pairs of hadrons established that high transverse momentum particles are produced from states with two roughly back-to-back jets which are the result of scattering of point-like constituents of the protons as described by QCD. In the region of hard-scattering, pT > 2 GeV/c, the scaling from p-p to nuclear collisions should be simply proportional to the relative number of point-like sources in each, corresponding to A (p+A), A^2 (A+A) for the total rate, and to Tab, the thickness function, as a function of centrality. Measurements of high pT pion production in p+A and A+A collisions at FERMILAB and CERN fixed target energies and at the CERN ISR, however, all showed an enhancement compared to the point-like scaling, a phenomenon known as ``the Cronin effect''. In stark contrast to the results at lower c.m. energies, measurements of high pT pizero production at $sqrt{s_{NN}}=130$ GeV from PHENIX at RHIC show a huge suppression compared to point-like scaling. Such an effect has been predicted in QCD, for a sufficiently hot, dense, and colorful medium, due to the interaction of the outgoing partons with the medium. The PHENIX results will be presented and discussed in the context of the nearly 30 year history of this subject, which originated at CERN.

Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann

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