Article

# A comparative measurement of and in In–In collisions at the CERN SPS

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05/2011; 699(5):325-329. DOI: 10.1016/j.physletb.2011.04.028
Source: arXiv

ABSTRACT

The NA60 experiment at the CERN SPS has studied $\phi$ meson production in
In-In collisions at 158A GeV via both the $K^+K^-$ and the $\mu^+\mu^-$ decay
channels. The yields and inverse slope parameters of the $m_T$ spectra observed
in the two channels are compatible within errors, different from the large
discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon
(NA50) decay channels. Possible physics implications are discussed.

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Physics Letters B 04/2012; 710(4-5-4-5):557-568. DOI:10.1016/j.physletb.2012.03.038 · 6.13 Impact Factor
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ABSTRACT: The NA60 experiment at the CERN SPS has studied light vector meson production in In-In collisions at 158A GeV. The ϕ meson was detected via both the K+K- and the μ+μ- decay channels. The yields and inverse slope parameters of the mT spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. In the invariant mass region 0.2 < Mμμ < 2.6 GeV, a strong excess of pairs above the sources that describe the mass spectrum in p-A collisions is observed. The mass spectrum for Mμμ < 1 GeV is consistent with a dominant contribution from the pion annihilation process π + π → ρ → μ+μ-. For Mμμ > 1 GeV, the excess is found to be prompt, with remarkable differences with respect to the Drell-Yan process. The Teff slope parameter, extracted from the transverse mass spectra, shows a rise with mass up to the ρ, followed by a sudden decline for higher masses. The former is consistent with radial flow of a hadronic source, while the latter suggests a dominantly partonic emission source.
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ABSTRACT: Vector mesons are key probes of the hot and dense state of strongly interacting matter produced in heavy ion collisions. Their dileptonic decay channel is particularly suitable for these studies, since dileptons have negligible final state interactions in hadronic matter. In particular, strangeness production can be studied through the measurement of muon pairs coming from the decay of phi mesons. The ALICE apparatus at the LHC can access vector mesons produced at forward rapidity (2.5 < y < 4) through their decays in muon pairs. We present results on vector meson production in pp and Pb-Pb collisions at root S-NN = 2.76 TeV. The phi meson production cross section is measured in pp collisions. In Pb-Pb collisions, a measurement of the phi/(rho + omega) ratio and of the phi nuclear modification factor as a function of the collision centrality is obtained.
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