Abstract
We report first measurements of e+e− pair production in the mass region 0.4 < Mee < 2.6 GeV/c2 at low transverse momentum (pT < 0.15 GeV/c) in noncentral Au+Au collisions at √sNN = 200 GeV and U+U collisions at √sNN = 193 GeV. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40%–80% centrality of these collisions. The excess yields peak distinctly at low pT with a width (√⟨p2T⟩) between 40 and 60 MeV/c. The absolute cross section of the excess depends weakly on centrality, while those from a theoretical model calculation incorporating an in-medium broadened ρ spectral function and radiation from a quark gluon plasma or hadronic cocktail contributions increase dramatically with an increasing number of participant nucleons. Model calculations of photon-photon interactions generated by the initial projectile and target nuclei describe the observed excess yields but fail to reproduce the p2T distributions.
Document Type
Article
Publication Date
9-25-2018
Digital Object Identifier (DOI)
https://doi.org/10.1103/PhysRevLett.121.132301
Funding Information
Funded by SCOAP3.
This work was supported in part by the Office of Nuclear Physics within the U.S. DOE Office of Science, the U.S. National Science Foundation, the Ministry of Education and Science of the Russian Federation, National Natural Science Foundation of China, Chinese Academy of Science, the Ministry of Science and Technology of China and the Chinese Ministry of Education, the National Research Foundation of Korea, Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic, Department of Atomic Energy and Department of Science and Technology of the Government of India, the National Science Centre of Poland, the Ministry of Science,Education and Sports of the Republic of Croatia, RosAtom of Russia, and German Bundesministerium fur Bildung, Wissenschaft, Forschung and Technologie (BMBF) and the Helmholtz Association.
Repository Citation
Adam, J.; Adamczyk, L.; Adams, J. R.; Adkins, James K.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Ajitanand, N. N.; Alekseev, I.; Anderson, D. M.; Aoyama, R.; Aparin, A.; Arkhipkin, D.; Aschenauer, E. C.; Ashraf, M. U.; Atetalla, F.; Attri, A.; Averichev, G. S.; Bai, X.; Bairathi, V.; Barish, K.; Bassill, A. J.; Behera, A.; Bellwied, R.; Bhasin, A.; Bhati, A. K.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Bordyuzhin, I. G.; Fatemi, Renee H.; and Ramachandran, Suvarna, "Low-pT e+ e- Pair Production in Au + Au Collisions at √sNN = 193 GeV and U + U Collisions at √sNN = 193 GeV at STAR" (2018). Physics and Astronomy Faculty Publications. 624.
https://uknowledge.uky.edu/physastron_facpub/624
Notes/Citation Information
Published in Physical Review Letters, v. 121, issue 13, 132301, p. 1-8.
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.
Due to the large number of authors, only the first 30 and the authors affiliated with the University of Kentucky are listed in the author section above. For the complete list of authors, please download this article or visit: https://doi.org/10.1103/PhysRevLett.121.132301
This group of authors is collectively known as the STAR Collaboration.