Abstract
The PHENIX collaboration presents first measurements of low-momentum () direct-photon yields from collisions at 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 collisions at . Analyzing the photon yield as a function of the experimental observable reveals that the low-momentum () direct-photon yield is a smooth function of and can be well described as proportional to with . 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 collision systems. At a given beam energy, the scaling also holds for high (), but when results from different collision energies are compared, an additional -dependent multiplicative factor is needed to describe the integrated-direct-photon yield.
- Received 15 May 2018
- Revised 27 April 2019
DOI:https://doi.org/10.1103/PhysRevLett.123.022301
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society