# 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.
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http://hal.in2p3.fr/in2p3-00342023
Contributor : Jeanine Pellet <>
Submitted on : Wednesday, November 26, 2008 - 3:21:16 PM
Last modification on : Thursday, February 25, 2021 - 10:58:19 AM

### Identifiers

• HAL Id : in2p3-00342023, version 1
• ARXIV : 0806.0577

### Citation

R. Arnaldi, K. Banicz, J. Castor, B. Chaurand, C. Cicalò, et al.. Thermal Dimuon Emission in In-In at the CERN SPS. 2008. ⟨in2p3-00342023⟩

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