Systematic Study of High pT Hadron Spectra in pp, pA and AA Collisions from SPS to RHIC Energies
نویسنده
چکیده
High-pT particle spectra in p+p (p+̄p), p+A and A+B collisions are calculated within a lowest-order (LO) perturbative QCD (pQCD) parton model, including intrinsic transverse momentum, its broadening due to initial multiple parton scattering and jet quenching due to parton energy loss inside a dense medium. The intrinsic kT and its broadening in p+A and A+B collisions due to initial multiple parton scattering are found to be very important at low energies ( √ s < 50 GeV), and they decrease with energy and transverse momentum. Comparisons with S + S, S +Au and Pb+ Pb data with different centrality cuts show that the differential cross sections of large transverse momentum pion production (pT > 1 GeV/c) in A + B collisions scale very well with the number of binary nucleon-nucleon collisions (modulo effects of multiple initial scattering). This indicates that semi-hard parton scattering is the dominant particle production mechanism underlying the hadron spectra at moderate pT > ∼ 1 GeV/c. However, there is no evidence of jet quenching or parton energy loss. Within the parton model, one can exclude an effective parton energy loss dEq/dx > 0.01 GeV/fm and a mean free path λq < 7 fm from the experimental data of A + B collisions at the SPS energies. Predictions for high pT particle spectra in p + A and A + A collisions with and without jet quenching at the RHIC energy are also given. Uncertainties due to initial multiple scattering and nuclear shadowing of parton distributions are also discussed
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