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.

Thermal Dimuon Emission in In-In at the CERN SPS

FERRETTI, Alessandro;
2008-01-01

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.
2008
43rd Rencontres de Moriond on Electroweak Interactions and Unified Theories
La Thuile, Italy
1-8 Mar 2008
Proceedings of the 43rd Rencontres de Moriond on Electrowek Interactions and Unified Theories
The Gioi Publishers
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http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.0577v1.pdf
R. Arnaldi; K. Banicz; J. Castor; B. Chaurand; C. Cicalo; A. Colla; P. Cortese; S. Damjanovic; A. David; A. de Falco; A. Devaux; L. Ducroux; H. En'yo; J. Farjeix; A. Ferretti; M. Floris; A. F orster; P. Force; N. Guettet; A. Guichard; H. Gulkanyan; J. Heuser; M. Keil; L. Kluberg; C. Lourenco; J. Lozano; F. Manso; P. Martins; A. Masoni; A. Neves; H. Ohnishi; C. Oppedisano; P. Parracho; P. Pillot; T. Poghosyan; G. Puddu; E. Radermacher; P. Ramalhete; P. Rosinsky; E. Scomparin; J. Seixas; S. Serci; R. Shahoyan; P. Sonderegger; H.J. Specht; R. Tieulent; G. Usai; R. Veenhof; H.K. W ohri
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1512494
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