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arXiv · 1204.1526

Evolution of pi^0 suppression in Au+Au collisions from sqrt(s_NN) = 39 to 200 GeV

A. Adare·S. Afanasiev·C. Aidala·N. N. Ajitanand·Y. Akiba·R. Akimoto·H. Al-Ta'ani·J. Alexander·A. Angerami·K. Aoki·N. Apadula·Y. Aramaki·H. Asano·E. C. Aschenauer·E. T. Atomssa·T. C. Awes·B. Azmoun·V. Babintsev·M. Bai·B. Bannier·K. N. Barish·B. Bassalleck·S. Bathe·V. Baublis·S. Baumgart·A. Bazilevsky·R. Belmont·A. Berdnikov·Y. Berdnikov·X. Bing·D. S. Blau·K. Boyle·M. L. Brooks·H. Buesching·V. Bumazhnov·S. Butsyk·S. Campbell·P. Castera·C. -H. Chen·C. Y. Chi·M. Chiu·I. J. Choi·J. B. Choi·S. Choi·R. K. Choudhury·P. Christiansen·T. Chujo·O. Chvala·V. Cianciolo·Z. Citron·B. A. Cole·M. Connors·M. Csanád·T. Csörgő·S. Dairaku·A. Datta·M. S. Daugherity·G. David·A. Denisov·A. Deshpande·E. J. Desmond·K. V. Dharmawardane·O. Dietzsch·L. Ding·A. Dion·M. Donadelli·O. Drapier·A. Drees·K. A. Drees·J. M. Durham·A. Durum·L. D'Orazio·S. Edwards·Y. V. Efremenko·T. Engelmore·A. Enokizono·S. Esumi·K. O. Eyser·B. Fadem·D. E. Fields·M. Finger·M. Finger Jr·F. Fleuret·S. L. Fokin·J. E. Frantz·A. Franz·A. D. Frawley·Y. Fukao·T. Fusayasu·K. Gainey·C. Gal·A. Garishvili·I. Garishvili·A. Glenn·X. Gong·M. Gonin·Y. Goto·R. Granier de Cassagnac·N. Grau·S. V. Greene
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Abstract

Neutral-pion, pi^0, spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at sqrt(s_NN) = 39 and 62.4 GeV and compared to earlier measurements at 200 GeV in the 1<p_T<10 GeV/c transverse-momentum (p_T) range. The high-p_T tail is well described by a power law in all cases and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding p+p-collision spectra. The nuclear-modification factors (R_AA) show significant suppression and a distinct energy dependence at moderate p_T in central collisions. At high p_T, R_AA is similar for 62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R_AA well at 200 GeV, fail to describe the 39 GeV data, raising the possibility that the relative importance of initial-state effects and soft processes increases at lower energies. A conclusion that the region where hard processes are dominant is reached only at higher p_T, is also supported by the x_T dependence of the x_T-scaling power-law exponent.

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A. Adare, S. Afanasiev, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, H. Al-Ta'ani, J. Alexander, A. Angerami, K. Aoki, N. Apadula, Y. Aramaki, H. Asano, E. C. Aschenauer, E. T. Atomssa, T. C. Awes, B. Azmoun, V. Babintsev, M. Bai, B. Bannier, K. N. Barish, B. Bassalleck, S. Bathe, V. Baublis, S. Baumgart, A. Bazilevsky, R. Belmont, A. Berdnikov, Y. Berdnikov, X. Bing, D. S. Blau, K. Boyle, M. L. Brooks, H. Buesching, V. Bumazhnov, S. Butsyk, S. Campbell, P. Castera, C. -H. Chen, C. Y. Chi, M. Chiu, I. J. Choi, J. B. Choi, S. Choi, R. K. Choudhury, P. Christiansen, T. Chujo, O. Chvala, V. Cianciolo, Z. Citron, B. A. Cole, M. Connors, M. Csanád, T. Csörgő, S. Dairaku, A. Datta, M. S. Daugherity, G. David, A. Denisov, A. Deshpande, E. J. Desmond, K. V. Dharmawardane, O. Dietzsch, L. Ding, A. Dion, M. Donadelli, O. Drapier, A. Drees, K. A. Drees, J. M. Durham, A. Durum, L. D'Orazio, S. Edwards, Y. V. Efremenko, T. Engelmore, A. Enokizono, S. Esumi, K. O. Eyser, B. Fadem, D. E. Fields, M. Finger, M. Finger Jr, F. Fleuret, S. L. Fokin, J. E. Frantz, A. Franz, A. D. Frawley, Y. Fukao, T. Fusayasu, K. Gainey, C. Gal, A. Garishvili, I. Garishvili, A. Glenn, X. Gong, M. Gonin, Y. Goto, R. Granier de Cassagnac, N. Grau, S. V. Greene. 2012-04-06. Evolution of pi^0 suppression in Au+Au collisions from sqrt(s_NN) = 39 to 200 GeV. https://doi.org/10.1103/physrevlett.109.152301%2010.1103%2Fphysrevlett.125.049901

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