Abstract
The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c 2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c 2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c 2 to be of largely partonic origin, when radial flow has not yet built up.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
E.V. Shuryak, Phys. Rep. 61, 71 (1980)
J. Kapusta, P. Lichard, D. Seibert, Phys. Rev. D 44, 2774 (1991)
P.V. Ruuskanen, Nucl. Phys. A 544, 169c (1992)
G.Q. Li, C. Gale, Phys. Rev. Lett. 81, 1572 (1998)
C. Lourenço et al. (NA38 Collaboration), Nucl. Phys. A 566, 77c (1994)
A.L.S. Angelis et al. (HELIOS-3 Collaboration), Eur. Phys. J. C 13, 433 (2000)
M.C. Abreu et al. (NA50 Collaboration), Eur. Phys. J. C 14, 443 (2000)
C. Soave, Tesi di Dottorato di Ricerca, Universita degli studi di Torino, April 1998
L. Capelli et al. (NA38/NA50 Collaboration), Nucl. Phys. A 698, 539c (2002)
R. Rapp, E. Shuryak, Phys. Lett. B 473, 13 (2000)
P. Lévai, B. Müller, X.-N. Wang, Phys. Rev. C 51, 3326 (1995)
Z. Lin, X.-N. Wang, Phys. Lett. B 444, 245 (1998)
J.W. Qiu, X.F. Zhang, Phys. Lett. B 525, 265 (2002)
C. Spieles et al., Eur. Phys. J. C 5, 349 (1998)
R. Shahoyan, Physica G 34, 1029 (2007)
M.C. Abreu et al. (NA50 Collaboration), Phys. Lett. B 410, 327 (1997)
M. Keil et al., Nucl. Instrum. Methods A 549, 20 (2005)
S. Damjanovic et al. (NA60 Collaoration), Eur. Phys. J. C 49, 235 (2007)
S. Damjanovic et al., Nucl. Phys. A 783, 327 (2007)
A. David, PhD thesis, Instituto Superior Técnico, Universidade Técnica de Lisboa, 2005 (CERN-THESIS-2006-007)
K. Wyllie et al., in Proc. of the Fifth Workshop on Electronics for LHC Experiments, Snowmass, CO, 1999
L. Casagrande et al., Nucl. Instrum. Methods A 478, 325 (2002)
T. Sjöstrand et al., Comput. Phys. Commun. 135, 238 (2001)
J. Pumplin et al., J. High Energy Phys. 07, 012 (2002)
K.J. Eskola, V.J. Kolhinen, C.A. Salgado, Eur. Phys. J. C 9, 61 (1999)
H.K. Wöhri, C. Lourenço, J. Phys. G 30, S315 (2004)
C. Lourenço, H.K. Wöhri, Phys. Rep. 433, 127 (2006)
A. David, Phys. Lett. B 644, 224 (2007)
GEANT, http://wwasd.web.cern.ch/wwwasd/geant
M. Floris et al. (NA60 Collaboration), Phys. Conf. Ser. 5, 55–63 (2005)
J. Badier et al. (NA3 Collaboration), Z. Phys. C 26, 489 (1985)
M.C. Abreu et al. (NA50 Collaboration), Phys. Lett. B 410, 337 (1997)
B. Alessandro et al. (NA50 Collaboration), Eur. Phys. J. C 39, 335 (2007)
R. Arnaldi et al. (NA60 Collaboration), Phys. Rev. Lett. 99, 132302 (2007)
G. Moreno et al., Phys. Rev. D 43, 2815 (1991)
R. Arnaldi et al. (NA60 Collaboration), Phys. Rev. Lett. 100, 022302 (2008)
S. Damjanovic et al. (NA60 Collaboration), 0805.4153 [nucl-ex]
S. Damjanovic et al. (NA60 Collaboration), in Proceedings of Hard Probes 2008 Conference. 0812.3053v1 [nucl-ex]
H. van Hees, R. Rapp, Nucl. Phys. A 806, 339 (2008)
J. Ruppert, C. Gale, T. Renk, P. Litchard, J. Kapusta, Phys. Rev. Lett. 100, 162301 (2008)
T. Renk, J. Ruppert, Phys. Rev. C 77, 024907 (2008)
K. Dusling, D. Teaney, I. Zahed, Phys. Rev. C 75, 024908 (2007). hep-ph/0701253
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License ( https://creativecommons.org/licenses/by-nc/2.0 ), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
About this article
Cite this article
Arnaldi, R., Banicz, K., Borer, K. et al. Evidence for the production of thermal muon pairs with masses above 1 GeV/c 2 in 158 A GeV indium-indium collisions. Eur. Phys. J. C 59, 607–623 (2009). https://doi.org/10.1140/epjc/s10052-008-0857-2
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1140/epjc/s10052-008-0857-2