First Measurement of the {rho} Spectral Function in High-Energy Nuclear Collisions

Journal Article · Fri Apr 28 00:00:00 EDT 2006 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.96.162302· OSTI ID:20775182

Arnaldi, R; Colla, A; Cortese, P; Ferretti, A; Oppedisano, C; Scomparin, E ^[1]; Averbeck, R; Drees, A ^[2]; Banicz, K; Specht, H J ^[3]; CERN, Geneva ^[4]; Castor, J; Devaux, A; Fargeix, J; Force, P; Manso, F ^[5]; Chaurand, B ^[6]; Cicalo, C; De Falco, A; Floris, M ; Masoni, A ^[7]

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1. Universita di Torino and INFN, Turin (Italy)
2. SUNY, Stony Brook, New York (United States)
3. Universitaet Heidelberg, Heidelberg (Germany)
4. Switzerland
5. LPC, Universite Blaise Pascal and CNRS-IN2P3, Clermont-Ferrand (France)
6. LLR, Ecole Polytechnique and CNRS-IN2P3, Palaiseau (France)
7. Universita di Cagliari and INFN, Cagliari (Italy)

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}{sup +}{pi}{sup -}{yields}{rho}{yields}{mu}{sup +}{mu}{sup -} annihilation. The associated space-time averaged {rho} 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.

• OSTI ID: 20775182
• Journal Information: Physical Review Letters, Vol. 96, Issue 16; Other Information: DOI: 10.1103/PhysRevLett.96.162302; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0031-9007
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANNIHILATION
CERN SPS SYNCHROTRON
CHIRALITY
COLLIDING BEAMS
HEAVY ION REACTIONS
INDIUM
LEPTONIC DECAY
MASS RESOLUTION
MASS SPECTRA
MUON PAIRS
MUONS MINUS
MUONS PLUS
PAIR PRODUCTION
PION-PION INTERACTIONS
PIONS MINUS
PIONS PLUS
QUANTUM CHROMODYNAMICS
RHO-770 MESONS
SPACE-TIME
SPECTRAL FUNCTIONS