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The European Physical Journal C

, Volume 61, Issue 4, pp 711–720 | Cite as

NA60 results on thermal dimuons

  • NA60 Collaboration
  • R. Arnaldi
  • K. Banicz
  • K. Borer
  • J. Castor
  • B. Chaurand
  • W. Chen
  • C. Cicalò
  • A. Colla
  • P. Cortese
  • S. Damjanovic
  • A. David
  • A. de Falco
  • A. Devaux
  • L. Ducroux
  • H. En’yo
  • J. Fargeix
  • A. Ferretti
  • M. Floris
  • A. Förster
  • P. Force
  • N. Guettet
  • A. Guichard
  • H. Gulkanian
  • J. M. Heuser
  • M. Keil
  • L. Kluberg
  • Z. Li
  • C. Lourenço
  • 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. Wöhri
Open Access
Regular Article - Experimental Physics

Abstract

The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158 A 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 π + π ρμ + μ annihilation. The associated ρ 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 T eff associated with the transverse momentum spectra rises with mass up to the ρ, 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 p T and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on ω in-medium effects.

PACS

25.75.-q 12.38.Mh 13.85.Qk 

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Copyright information

© Springer-Verlag / Società Italiana di Fisica 2009

Authors and Affiliations

  • NA60 Collaboration
  • R. Arnaldi
    • 11
  • K. Banicz
    • 4
    • 6
  • K. Borer
    • 1
  • J. Castor
    • 5
  • B. Chaurand
    • 9
  • W. Chen
    • 2
  • C. Cicalò
    • 3
  • A. Colla
    • 11
  • P. Cortese
    • 11
  • S. Damjanovic
    • 4
  • A. David
    • 4
    • 7
  • A. de Falco
    • 3
  • A. Devaux
    • 5
  • L. Ducroux
    • 8
  • H. En’yo
    • 10
  • J. Fargeix
    • 5
  • A. Ferretti
    • 11
  • M. Floris
    • 3
  • A. Förster
    • 4
  • P. Force
    • 5
  • N. Guettet
    • 4
    • 5
  • A. Guichard
    • 8
  • H. Gulkanian
    • 12
  • J. M. Heuser
    • 10
  • M. Keil
    • 4
    • 7
  • L. Kluberg
    • 9
  • Z. Li
    • 2
  • C. Lourenço
    • 4
  • J. Lozano
    • 7
  • F. Manso
    • 5
  • P. Martins
    • 4
    • 7
  • A. Masoni
    • 3
  • A. Neves
    • 7
  • H. Ohnishi
    • 10
  • C. Oppedisano
    • 11
  • P. Parracho
    • 4
    • 7
  • P. Pillot
    • 8
  • T. Poghosyan
    • 12
  • G. Puddu
    • 3
  • E. Radermacher
    • 4
  • P. Ramalhete
    • 4
    • 7
  • P. Rosinsky
    • 4
  • E. Scomparin
    • 11
  • J. Seixas
    • 7
  • S. Serci
    • 3
  • R. Shahoyan
    • 4
    • 7
  • P. Sonderegger
    • 7
  • H. J. Specht
    • 6
  • R. Tieulent
    • 8
  • G. Usai
    • 3
  • R. Veenhof
    • 7
  • H. K. Wöhri
    • 3
    • 7
  1. 1.Laboratory for High Energy PhysicsBernSwitzerland
  2. 2.BNLUptonUSA
  3. 3.Università di Cagliari and INFNCagliariItaly
  4. 4.CERNGenevaSwitzerland
  5. 5.LPCUniversité Blaise Pascal and CNRS-IN2P3Clermont-FerrandFrance
  6. 6.Physikalisches Institut der Universität HeidelbergHeidelbergGermany
  7. 7.IST-CFTPLisbonPortugal
  8. 8.IPN-LyonUniv. Claude Bernard Lyon-I and CNRS-IN2P3LyonFrance
  9. 9.LLREcole Polytechnique and CNRS-IN2P3PalaiseauFrance
  10. 10.RIKENWakoJapan
  11. 11.Università di Torino and INFNTorinoItaly
  12. 12.YerPhIYerevanArmenia

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