Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions.



Adare, A, Afanasiev, S, Aidala, C, Ajitanand, NN, Akiba, Y, Akimoto, R, Al-Bataineh, H, Alexander, J, Alfred, M, Al-Jamel, A
et al (show 664 more authors) (2019) Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions. Physical review letters, 123 (2). 022301 - ?.

Access the full-text of this item by clicking on the Open Access link.

Abstract

The PHENIX collaboration presents first measurements of low-momentum (0.4<p_{T}<3  GeV/c) direct-photon yields from Au+Au collisions at sqrt[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+Au collisions at sqrt[s_{NN}]=200. Analyzing the photon yield as a function of the experimental observable dN_{ch}/dη reveals that the low-momentum (>1  GeV/c) direct-photon yield dN_{γ}^{dir}/dη is a smooth function of dN_{ch}/dη and can be well described as proportional to (dN_{ch}/dη)^{α} with α≈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+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 sqrt[s_{NN}]-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.

Item Type: Article
Uncontrolled Keywords: PHENIX Collaboration
Depositing User: Symplectic Admin
Date Deposited: 04 Dec 2019 15:13
Last Modified: 02 Nov 2020 18:11
DOI: 10.1103/physrevlett.123.022301
Open Access URL: https://doi.org/10.1103/PhysRevLett.123.022301
URI: http://livrepository.liverpool.ac.uk/id/eprint/3064806