Physics & Astronomy Faculty and Staff Publications

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Background: Heavy-flavor production in p+p collisions is a good test of perturbative-quantum- chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p+p results, quantified with the nuclear-modification factor (RAA), provides information on both cold- and hot-nuclear-matter effects. Midrapidity heavy-flavor RAA measurements at RHIC have challenged parton-energy-loss models and resulted in upper limits on the viscosity/entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region. Purpose: Determine transverse-momentum, pT spectra and the corresponding RAA for muons from heavy-flavor mesons decay in p+p and Cu+Cu collisions at √sNN = 200GeV and y = 1.65. Method: Results are obtained using the semi-leptonic decay of heavy-flavor mesons into negative muons. The PHENIX muon-arm spectrometers measure the pT spectra of inclusive muon candidates. Backgrounds, primarily due to light hadrons, are determined with a Monte-Carlo calculation using a set of input hadron distributions tuned to match measured-hadron distributions in the same detector and statistically subtracted. Results: The charm-production cross section in p+p collisions at √s = 200GeV, integrated over pT and in the rapidity range 1.4 < y < 1.9 is found to be dσc¯c/dy = 0.139 ± 0.029 (stat) +0.051−0.058 (syst) mb. This result is consistent with a perturbative fixed-order-plus-next-to-leading-log (FONLL) calculation within scale uncertainties and is also consistent with expectations based on the corresponding midrapidity charm-production cross section measured by PHENIX. The RAA for heavy-flavor muons in Cu+Cu collisions is measured in three centrality intervals for 1 < pT < 4 GeV/c. Suppression relative to binary-collision scaling (RAA < 1) increases with centrality. Conclusions: Within experimental and theoretical uncertainties, the measured heavy-flavor yield in p+p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu+Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.

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