CERN Accelerating science

Article
Report number arXiv:0812.3053
Title NA60 results on thermal dimuons
Author(s) NA60 collaboration  Mostrar todos os 52 autores
Publication 2009
Imprint 17 Dec 2008
Number of pages 10
Note Comments: 10 pages, 12 figures, submitted to Eur. Phys. J. C
10 pages, 12 figures, submitted to Eur. Phys. J. C
In: Eur. Phys. J. C 61 (2009) 711-720
DOI 10.1140/epjc/s10052-009-0878-5
Subject category Nuclear Physics - Experiment
Accelerator/Facility, Experiment CERN SPS ; NA60
Abstract The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158A GeV In-In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The mass spectrum for M<1 GeV is consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell-Yan pairs. The slope parameter Teff associated with the transverse momentum spectra rises with mass up to the rho, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton-hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low pT and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on omega in-medium effects.



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 Record created 2008-12-17, last modified 2023-03-14


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