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Arnaldi R, Banicz K, Castor J, Chaurand B, Cicalò C, Colla A, Cortese P, Damjanovic S, David A, de Falco A, Devaux A, Ducroux L, En'yo H, Fargeix J, Ferretti A, Floris M, Förster A, Force P, Guettet N, Guichard A, Gulkanian H, Heuser JM, Keil M, Kluberg L, Lourenço C, Lozano J, Manso F, Martins P, Masoni A, Neves A, Ohnishi H, Oppedisano C, Parracho P, Pillot P, Poghosyan T, Puddu G, Radermacher E, Ramalhete P, Rosinsky P, Scomparin E, Seixas J, Serci S, Shahoyan R, Sonderegger P, Specht HJ, Tieulent R, Usai G, Veenhof R, Wöhri HK. First results on angular distributions of thermal dileptons in nuclear collisions. Phys Rev Lett 2009; 102:222301. [PMID: 19658858 DOI: 10.1103/physrevlett.102.222301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Indexed: 05/28/2023]
Abstract
The NA60 experiment at the CERN Super Proton Synchrotron 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.
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Affiliation(s)
- R Arnaldi
- Università di Torino and INFN, Italy
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Arnaldi R, Banicz K, Castor J, Chaurand B, Cicalò C, Colla A, Cortese P, Damjanovic S, David A, de Falco A, Devaux A, Ducroux L, En'yo H, Fargeix J, Ferretti A, Floris M, Förster A, Force P, Guettet N, Guichard A, Gulkanian H, Heuser JM, Keil M, Kluberg L, Lourenço C, Lozano J, Manso F, Martins P, Masoni A, Neves A, Ohnishi H, Oppedisano C, Parracho P, Pillot P, Poghosyan T, Puddu G, Radermacher E, Ramalhete P, Rosinsky P, Scomparin E, Seixas J, Serci S, Shahoyan R, Sonderegger P, Specht HJ, Tieulent R, Usai G, Veenhof R, Wöhri HK. Evidence for radial flow of thermal dileptons in high-energy nuclear collisions. Phys Rev Lett 2008; 100:022302. [PMID: 18232858 DOI: 10.1103/physrevlett.100.022302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2007] [Indexed: 05/25/2023]
Abstract
The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff 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 signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.
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Affiliation(s)
- R Arnaldi
- Università di Torino and INFN, Torino, Italy
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Arnaldi R, Banicz K, Castor J, Chaurand B, Cicalò C, Colla A, Cortese P, Damjanovic S, David A, de Falco A, Devaux A, Ducroux L, En'yo H, Fargeix J, Ferretti A, Floris M, Förster A, Force P, Guettet N, Guichard A, Gulkanian H, Heuser JM, Keil M, Kluberg L, Lourenço C, Lozano J, Manso F, Martins P, Masoni A, Neves A, Ohnishi H, Oppedisano C, Parracho P, Pillot P, Poghosyan T, Puddu G, Radermacher E, Ramalhete P, Rosinsky P, Scomparin E, Seixas J, Serci S, Shahoyan R, Sonderegger P, Specht HJ, Tieulent R, Usai G, Veenhof R, Wöhri HK. J/psi production in Indium-Indium collisions at 158 GeV/nucleon. Phys Rev Lett 2007; 99:132302. [PMID: 17930580 DOI: 10.1103/physrevlett.99.132302] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Indexed: 05/25/2023]
Abstract
The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. 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 approximately 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.
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Affiliation(s)
- R Arnaldi
- Università di Torino and INFN, Italy
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Arnaldi R, Averbeck R, Banicz K, Castor J, Chaurand B, Cicalò C, Colla A, Cortese P, Damjanovic S, David A, De Falco A, Devaux A, Drees A, Ducroux L, En'yo H, Fargeix J, Ferretti A, Floris M, Förster A, Force P, Guettet N, Guichard A, Gulkanian H, Heuser JM, Keil M, Kluberg L, Lourenço C, Lozano J, Manso F, Masoni A, Martins P, Neves A, Ohnishi H, Oppedisano C, Parracho P, Pillot P, Puddu G, Radermacher E, Ramalhete P, Rosinsky P, Scomparin E, Seixas J, Serci S, Shahoyan R, Sonderegger P, Specht HJ, Tieulent R, Usai G, Veenhof R, Wöhri HK. First measurement of the rho spectral function in high-energy nuclear collisions. Phys Rev Lett 2006; 96:162302. [PMID: 16712218 DOI: 10.1103/physrevlett.96.162302] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2005] [Indexed: 05/09/2023]
Abstract
We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of 360,000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from pi+pi- -->rho -->mu+mu- annihilation. The associated space-time averaged spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.
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Affiliation(s)
- R Arnaldi
- Università di Torino and INFN, Turin, Italy
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