First Results on Angular Distributions of Thermal Dileptons in Nuclear Collisions

Journal Article · Fri Jun 05 00:00:00 EDT 2009 · Physical Review Letters

DOI:https://doi.org/10.1103/PHYSREVLETT.102.222301· OSTI ID:21325530

Arnaldi, R; Colla, A; Cortese, P; Ferretti, A; Oppedisano, C; Scomparin, E ^[1]; Banicz, K; Damjanovic, S ^[2]; Castor, J; Devaux, A; Fargeix, J; Force, P; Manso, F ^[3]; Chaurand, B ^[4]; Cicalo, C; Falco, A de; Floris, M; Masoni, A; Puddu, G; Serci, S ^[5]

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1. Universita di Torino and INFN (Italy)
2. CERN, 1211 Geneva 23 (Switzerland)
3. LPC, Universite Blaise Pascal and CNRS-IN2P3, Clermont-Ferrand (France)
4. LLR, Ecole Polytechnique and CNRS-IN2P3, Palaiseau (France)
5. Universita di Cagliari and INFN, Cagliari (Italy)

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.

• OSTI ID: 21325530
• Journal Information: Physical Review Letters, Vol. 102, Issue 22; Other Information: DOI: 10.1103/PhysRevLett.102.222301; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0031-9007
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANGULAR DISTRIBUTION
GEV RANGE 01-10
MEV RANGE 100-1000
PROTONS
STRUCTURE FUNCTIONS
THERMAL RADIATION