Abstract
The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 A∈GeV In-In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size close to 400000 events and the good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution from π+π -→ →μ+μ- annihilation. The associated Q spectral function exhibits considerable broadening, but essentially no shift in mass. The pT-differential mass spectra show the excess to be much stronger at low pT than at high pT. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to the chiral condensate.
Lingua originale | Inglese |
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pagine (da-a) | 235-241 |
Numero di pagine | 7 |
Rivista | European Physical Journal C |
Volume | 49 |
Numero di pubblicazione | 1 |
DOI | |
Stato di pubblicazione | Pubblicato - gen 2007 |
Pubblicato esternamente | Sì |