NA60 Collaboration

Publications (5)7.37 Total impact

• Source

  Available from: ArXiv

  Article: Study of the electromagnetic transition form-factors in \eta -> \mu^+\mu^-\gamma and \omega -> \mu^+\mu^-\pi^0 decays with NA60

  NA60 Collaboration, R. Arnaldi
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  ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158A GeV In-In collisions. The mass and pT spectra associated with peripheral collisions can quantitatively be described by the known neutral meson decays. The high data quality has allowed to remeasure the electromagnetic transition form factors of the Dalitz decays \eta -> \mu^+\mu^-\gamma and \omega -> \mu^+\mu^-\pi^0. Using the usual pole approximation F = (1-M_{\mu\mu}^{2}/\Lambda^{2})^{-1} for the form factors, we find \Lambda^{-2} (in GeV^{-2}) to be 1.95+-0.17(stat.)+-0.05(syst.) for the \eta and 2.24+-0.06(stat.)+-0.02(syst.) for the \omega. While the values agree with previous results from the Lepton-G experiment, the errors are greatly improved, confirming now on the level of 10\sigma the strong enhancement of the \omega form factor beyond the expectation from vector meson dominance. An improved value of the branching ratio BR(\omega -> \mu^+\mu^-\pi^0) = [1.73+-0.25(stat.)+-0.14(syst.)]*10^{-4} has been obtained as a byproduct. Comment: Submitted to Phys. Lett. B
  02/2009;
• Source

  Available from: Ernst Radermacher

  Article: First results on angular distributions of thermal dileptons in nuclear collisions

  NA60 Collaboration, R. Arnaldi, K Banicz, K Borer, J. Castor, B Chaurand, W Chen, C. Cicalo, A. Colla, P. Cortese, [......], E. Scomparin, J Seixas, S. Serci, R. Shahoyan, P Sonderegger, H J Specht, R. Tieulent, G. Usai, R Veenhof, H. K. Woehri
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  ABSTRACT: The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters \lambda, \mu and \nu are measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system. Comment: Submitted to Physical Review Letters
  Physical Review Letters 12/2008; · 7.37 Impact Factor
• Source

  Available from: Ernst Radermacher

  Article: NA60 results on thermal dimuons

  NA60 Collaboration, R. Arnaldi, K Banicz, K Borer, J. Castor, B Chaurand, W Chen, C. Cicalo, A. Colla, P. Cortese, [......], E. Scomparin, J Seixas, S. Serci, R. Shahoyan, P Sonderegger, H J Specht, R. Tieulent, G. Usai, R Veenhof, H. K. Woehri
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  ABSTRACT: The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158A GeV In-In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2<M<2.6 GeV. The mass spectrum for M<1 GeV is consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell-Yan pairs. The slope parameter Teff associated with the transverse momentum spectra rises with mass up to the rho, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton-hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low pT and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on omega in-medium effects. Comment: 10 pages, 12 figures, submitted to Eur. Phys. J. C
  12/2008;
• Source

  Available from: ArXiv

  Article: J/psi production in Indium-Indium collisions at 158 GeV/nucleon

  NA60 Collaboration, R. Arnaldi
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  ABSTRACT: The NA60 experiment studies muon pair production at the CERN SPS. In this letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than ~80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.
  07/2007;
• Source

  Available from: arxiv.org

  Article: NA60 results on the rho spectral function in In-In collisions

  S. Damjanovic, NA60 Collaboration
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  ABSTRACT: The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In-In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. After subtraction of the decay sources, the shape of the resulting mass spectrum is largely consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected pT spectra have a shape atypical for radial flow. They also significantly depend on mass, pointing to different sources in different mass regions. Both mass and pT spectra are compared to recent theoretical predictions.
  02/2007;