Journal
PHYSICAL REVIEW LETTERS
Volume 123, Issue 2, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.123.022301
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Funding
- Office of Nuclear Physics in the Office of Science of the Department of Energy (U.S.A)
- National Science Foundation (U.S.A)
- Abilene Christian University Research Council (U.S.A)
- Research Foundation of SUNY (U.S.A)
- College of Arts and Sciences, Vanderbilt University (U.S.A)
- Ministry of Education, Culture, Sports, Science, and Technology (Japan)
- Japan Society for the Promotion of Science (Japan)
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (Brazil)
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Brazil)
- Natural Science Foundation of China (People's Republic of China)
- Croatian Science Foundation (Croatia)
- Ministry of Science and Education (Croatia)
- Ministry of Education, Youth and Sports (Czech Republic)
- Centre National de la Recherche Scientifique (France)
- Commissariat a l'Energie Atomique (France)
- Institut National de Physique Nucleaire et de Physique des Particules (France)
- Bundesministerium fur Bildung und Forschung (Germany)
- Deutscher Akademischer Austausch Dienst (Germany)
- Alexander von Humboldt Stiftung (Germany)
- J. Bolyai Research Scholarship (Hungary)
- EFOP (Hungary)
- New National Excellence Program (UNKP) (Hungary)
- NKFIH (Hungary)
- OTKA (Hungary)
- Department of Atomic Energy and Department of Science and Technology (India)
- Israel Science Foundation (Israel)
- NRF of the Ministry of Education (Korea)
- Physics Department, Lahore University of Management Sciences (Pakistan)
- Ministry of Education and Science (Russia)
- Russian Academy of Sciences (Russia)
- Federal Agency of Atomic Energy (Russia)
- VR (Sweden)
- Wallenberg Foundation (Sweden)
- 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
- US-Israel Binational Science Foundation
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The PHENIX collaboration presents first measurements of low-momentum (0.4 < p(T) < 3 GeV/c) direct-photon yields from Au + Au collisions at root s(NN) =39 and 62.4 GeV. For both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in Au +horn Au collisions at root s(NN) =200. Analyzing the photon yield as a function of the experimental observable dN(ch)/d(eta) eveals that the low-momentum (> 1 GeV= c) direct-photon yield dN(gamma)(dir)/d(eta) is a smooth function f dN(ch)/d eta and can be well described as proportional to (dN(ch)/d(eta))(alpha) with a approximate to 1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A thorn A collision systems. At a given beam energy, the scaling also holds for high p(T) (> 5 GeV= c), but when results from different collision energies are compared, an additional root s(NN) -dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
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