Abstract
Neutral-pion π0 spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at √sNN=39 and 62.4GeV and compared with earlier measurements at 200GeV in a transverse-momentum range of 1<p T<10GeV/c. The high-pT 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 spectra for p+p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and pT dependence. Above pT=7GeV/c, R AA is similar for √sNN=62.4 and 200GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe RAA well at 200GeV fail to describe the 39GeV data, raising the possibility that, for the same pT region, the relative importance of initial-state effects and soft processes increases at lower energies. The p T range where π0 spectra in central Au+Au collisions have the same power as in p+p collisions is 5 and 7GeV/c for √sNN=200 and 62.4GeV, respectively. For the √sNN=39GeV data, it is not clear whether such a region is reached, and the xT dependence of the xT-scaling power-law exponent is very different from that observed in the √sNN=62 and 200GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher pT as the collision energy decreases.
| Original language | American English |
|---|---|
| Article number | 152301 |
| Journal | Physical Review Letters |
| Volume | 109 |
| Issue number | 15 |
| DOIs | |
| State | Published - 9 Oct 2012 |
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy
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In: Physical Review Letters, Vol. 109, No. 15, 152301, 09.10.2012.
Research output: Contribution to journal › Article › peer-review
TY - JOUR
T1 - Evolution of π0 suppression in Au+Au collisions from √s NN=39 to 200 GeV
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N1 - Office of Nuclear Physics in the Office of Science of the Department of Energy; National Science Foundation; Abilene Christian University Research Council; Research Foundation of SUNY; Dean of the College of Arts and Sciences, Vanderbilt University (U.S.A.); Ministry of Education, Culture, Sports, Science, and Technology; Japan Society for the Promotion of Science (Japan); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Brazil); Natural Science Foundation of China (P.R. China); Ministry of Education, Youth, and Sports (Czech Republic); Jyvaskyla University (Finland); Centre National de la Recherche Scientifique, Commissariat a l'Energie Atomique, (France); Institut National de Physique Nucleaire et de Physique des Particules (France); Bundesministerium fur Bildung und Forschung, Deutscher Akademischer Austausch Dienst, (Germany); Alexander von Humboldt Stiftung (Germany); Hungarian National Science Fund, OTKA (Hungary); Department of Atomic Energy (India); Department of Science and Technology (India); Israel Science Foundation (Israel); National Research Foundation (Korea); WCU Program of the Ministry of Education Science and Technology (Korea); Ministry of Education and Science, (Russia); Russian Academy of Sciences, (Russia); Federal Agency of Atomic Energy (Russia); VR and Wallenberg Foundation (Sweden); U.S. Civilian Research and Development Foundation for the Independent States of the Former Soviet Union; U.S.-Israel Binational Science FoundationWe thank the staff of the Collider-Accelerator and Physics Departments at Brookhaven National Laboratory and the staff of the other PHENIX participating institutions for their vital contributions. We also thank Ivan Vitev for valuable discussions and helpful suggestions for changes to the text. We acknowledge support from the Office of Nuclear Physics in the Office of Science of the Department of Energy, the National Science Foundation, Abilen
PY - 2012/10/9
Y1 - 2012/10/9
N2 - Neutral-pion π0 spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at √sNN=39 and 62.4GeV and compared with earlier measurements at 200GeV in a transverse-momentum range of 1T<10GeV/c. The high-pT 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 spectra for p+p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and pT dependence. Above pT=7GeV/c, R AA is similar for √sNN=62.4 and 200GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe RAA well at 200GeV fail to describe the 39GeV data, raising the possibility that, for the same pT region, the relative importance of initial-state effects and soft processes increases at lower energies. The p T range where π0 spectra in central Au+Au collisions have the same power as in p+p collisions is 5 and 7GeV/c for √sNN=200 and 62.4GeV, respectively. For the √sNN=39GeV data, it is not clear whether such a region is reached, and the xT dependence of the xT-scaling power-law exponent is very different from that observed in the √sNN=62 and 200GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher pT as the collision energy decreases.
AB - Neutral-pion π0 spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at √sNN=39 and 62.4GeV and compared with earlier measurements at 200GeV in a transverse-momentum range of 1T<10GeV/c. The high-pT 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 spectra for p+p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and pT dependence. Above pT=7GeV/c, R AA is similar for √sNN=62.4 and 200GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe RAA well at 200GeV fail to describe the 39GeV data, raising the possibility that, for the same pT region, the relative importance of initial-state effects and soft processes increases at lower energies. The p T range where π0 spectra in central Au+Au collisions have the same power as in p+p collisions is 5 and 7GeV/c for √sNN=200 and 62.4GeV, respectively. For the √sNN=39GeV data, it is not clear whether such a region is reached, and the xT dependence of the xT-scaling power-law exponent is very different from that observed in the √sNN=62 and 200GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher pT as the collision energy decreases.
UR - http://www.scopus.com/inward/record.url?scp=84867364497&partnerID=8YFLogxK
U2 - https://doi.org/10.1103/PhysRevLett.109.152301
DO - https://doi.org/10.1103/PhysRevLett.109.152301
M3 - Article
SN - 0031-9007
VL - 109
JO - Physical Review Letters
JF - Physical Review Letters
IS - 15
M1 - 152301
ER -