Abstract
PHENIX presents a simultaneous measurement of the production of direct γ and π0 in d+Au collisions at sNN=200 GeV over a pT range of 7.5 to 18 GeV/c for different event samples selected by event activity, i.e., charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor, RdAu,EXPπ0, is 0.925±0.023(stat)±0.15(scale), consistent with unity for minimum-bias (MB) d+Au collisions. For event classes with low and moderate event activity, RdAu,EXPπ0 is consistent with the MB value within 5% uncertainty. This result confirms that the previously observed enhancement of high-pT π0 production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5% of events with the highest event activity, RdAu,EXPπ0 is suppressed by 20% relative to the MB value with a significance of 4.5σ, which may be due to final-state effects. This suppression corresponds to a pT shift of δpT=0.213±0.055 Gev/c at 9 Gev/c.
| Original language | English |
|---|---|
| Article number | 022302 |
| Journal | Physical Review Letters |
| Volume | 134 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jan 17 2025 |
Funding
We 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 acknowledge support from the 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 (USA), Ministry of Education, Culture, Sports, Science, and Technology and the Japan Society for the Promotion of Science (Japan), Natural Science Foundation of China (People\u2019s Republic of China), Croatian Science Foundation and Ministry of Science and Education (Croatia), Ministry of Education, Youth and Sports (Czech Republic), Centre National de la Recherche Scientifique, Commissariat \u00E0 l\u2019\u00C9nergie Atomique, and Institut National de Physique Nucl\u00E9aire et de Physique des Particules (France), J. Bolyai Research Scholarship, EFOP, New National Excellence Program (\u00DANKP), NKFIH, and OTKA (Hungary), Department of Atomic Energy and Department of Science and Technology (India), Israel Science Foundation (Israel), Basic Science Research and SRC(CENuM) Programs through NRF funded by the Ministry of Education and the Ministry of Science and ICT (Korea), Ministry of Education and Science, Russian Academy of Sciences, Federal Agency of Atomic Energy (Russia), VR and Wallenberg Foundation (Sweden), University of Zambia, Government of the Republic of Zambia (Zambia), U.S. Civilian Research and Development Foundation for the Independent States of the Former Soviet Union, Hungarian American Enterprise Scholarship Fund, US-Hungarian Fulbright Foundation, and US-Israel Binational Science Foundation.