x_T scaling in Au+Au collisions for <pi>⁰ and charged hadrons from PHENIX

by Mike Tannenbaum (Brookhaven National Laboratory, PHENIX Coll.)

Tuesday 21 Oct 2003, 14:00 → 15:00 Europe/Zurich

40-SS-D01 (CERN)

The single particle inclusive cross section for hard parton-parton scattering can be written as G(x_T)/ \sqrt{s}ⁿ under the assumption of factorization of the reaction into scaling parton distribution and fragmentation functions together with a short-distance parton-parton hard scattering cross section. Here, n is a function of x_T=2p_T/ \sqrt{s} and \sqrt{s}. In LO QCD, n=4, as in Rutherford scattering, but due to higher order effects, measured values of n in p-p collisions are in the range 5-8. x_T scaling of the invariant yields is applied to high p_T charged particle and π⁰ production in Au+Au collisions at 130 and 200 GeV/A.The π⁰ exhibit x_T scaling with n ~ 6.3 for both central and peripheral collisions, while charged hadrons x_T scale with n ~ 6.3 for peripheral and n ~ 7.5 for central Au+Au collisions, where the value for pp collisions in this x_T range is n ~ 6.3. This indicates that the dynamics in Au+Au interactions for high p_T particle production are the same as in p-p collisions: hard-scattering according to pQCD with scaling structure and fragmentation functions. The significant difference in n for charged hadrons in central and peripheral collisions is traced to the non-scaling behavior of proton production in Au+Au central collisions. Protons are enhanced compared to pions, relative to jet fragmentation, over the range 2 < p_T < 4.5 GeV for both 130 and 200 GeV/A; a clear violation of x_T scaling. This argues for production dynamics different from pQCD for protons in this p_T range. PHENIX results from high p_T charged particle and π⁰ production in d+Au and p+p collisions at 200 GeV/A will also be presented.

Organiser(s): Yiota Foka and Urs Achim Wiedemann
More information: http://home.cern.ch/a/alicedoc/www/chic/

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