Thermal Dimuon Emission in In-In at the CERN SPS
Abstract
The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. A significant excess of pairs is observed above the yield expected from neutral meson decays, consistent with a dominant contribution from $\pi\pi\to\rho\to\mu\mu$. This paper presents precision results on the mass and transverse momentum spectra of the excess pairs. The space-time averaged rho spectral function associated to the measured mass distribution shows a significant broadening, but essentially no mass shift. The slope parameter $T_{eff}$ extracted from the spectra rises with dimuon mass up to the $\rho$, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline indicates a transition to an emission source with much smaller flow, possibly of partonic origin.
- Publication:
-
arXiv e-prints
- Pub Date:
- June 2008
- DOI:
- 10.48550/arXiv.0806.0577
- arXiv:
- arXiv:0806.0577
- Bibcode:
- 2008arXiv0806.0577F
- Keywords:
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- Nuclear Experiment
- E-Print:
- 4 pages, 4 figures, presented at the XLIIIth Rencontres de Moriond