The Mini-Jet Scale and Energy Loss at RHIC in the HIJING and RQMD Models
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X iv :n uc lth /0 20 90 89 v 4 1 4 A ug 2 00 3 The Mini-Jet Scale and Energy Loss at RHIC in the HIJING and RQMD Models V. Topor Pop, M. Gyulassy, J. Barrette, C. Gale, X. N. Wang, N. Xu, K. Filimonov 1McGill, University, Montreal, Canada, H3A 2T8 2Physics Department, Columbia University, New York, N.Y. 10027 3Nuclear Science Division, LBNL, Berkeley, CA 94720 (August 15, 2003) Recent data from Relativistic Heavy Ion Collider (RHIC) on rapidity and transverse momentum distributions of hadrons produced in ultra-relativistic reaction of both Au+Au and p+p are compared to predictions of the HIJING and RQMD models. The original default mini-jet scale p0 = 2 GeV/c and energy loss, dE/dx = 2 GeV/fm in HIJING lead to a too rapid growth of the multiplicity with energy. RQMD model without mini-jet leads on the other hand to a too slowly increasing multiplicity with energy. Therefore, we study what variations of p0 and dE/dx are required in HIJING to account for the observed Npart and √ s dependence of the global dNch/dy and dET /dy observables as well as the jet quenching pattern out to pT ∼ 8 GeV. We show that a slight increase of p0 from the default 2.0 GeV/c at √ s = 130A GeV to 2.2 GeV/c at √ s = 200A GeV is sufficient to account for the bulk observables. Jet quenching of π0 above pT > 4 GeV/c at 200A GeV is found to be well reproduced in central Au + Au by the original HIJING default prediction. However, the effective surface emission in the HIJING model formulation of energy loss over-predicts the quenching in more peripheral collisions. Neither HIJING nor HIJING/BB̄ can account for the observed anomalous excess of moderate pT < 4 GeV/c baryons. The agreement of RQMD with data in this pT region is shown to be fortuitous because, without mini-jets, it fails to
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