title: Evidence for radial flow of thermal dileptons in high-energy nuclear collisions.
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.
authors.affiliation: Università di Torino and INFN, Torino, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Arnaldi
authors.forename: K
authors.initials: K
authors.lastname: Banicz
authors.forename: J
authors.initials: J
authors.lastname: Castor
authors.forename: B
authors.initials: B
authors.lastname: Chaurand
authors.forename: C
authors.initials: C
authors.lastname: Cicalò
authors.forename: A
authors.initials: A
authors.lastname: Colla
authors.forename: P
authors.initials: P
authors.lastname: Cortese
authors.forename: S
authors.initials: S
authors.lastname: Damjanovic
authors.forename: A
authors.initials: A
authors.lastname: David
authors.forename: A
authors.initials: A
authors.lastname: de Falco
authors.forename: A
authors.initials: A
authors.lastname: Devaux
authors.forename: L
authors.initials: L
authors.lastname: Ducroux
authors.forename: H
authors.initials: H
authors.lastname: En'yo
authors.forename: J
authors.initials: J
authors.lastname: Fargeix
authors.forename: A
authors.initials: A
authors.lastname: Ferretti
authors.forename: M
authors.initials: M
authors.lastname: Floris
authors.forename: A
authors.initials: A
authors.lastname: Förster
authors.forename: P
authors.initials: P
authors.lastname: Force
authors.forename: N
authors.initials: N
authors.lastname: Guettet
authors.forename: A
authors.initials: A
authors.lastname: Guichard
authors.forename: H
authors.initials: H
authors.lastname: Gulkanian
authors.forename: J M
authors.initials: JM
authors.lastname: Heuser
authors.forename: M
authors.initials: M
authors.lastname: Keil
authors.forename: L
authors.initials: L
authors.lastname: Kluberg
authors.forename: C
authors.initials: C
authors.lastname: Lourenço
authors.forename: J
authors.initials: J
authors.lastname: Lozano
authors.forename: F
authors.initials: F
authors.lastname: Manso
authors.forename: P
authors.initials: P
authors.lastname: Martins
authors.forename: A
authors.initials: A
authors.lastname: Masoni
authors.forename: A
authors.initials: A
authors.lastname: Neves
authors.forename: H
authors.initials: H
authors.lastname: Ohnishi
authors.forename: C
authors.initials: C
authors.lastname: Oppedisano
authors.forename: P
authors.initials: P
authors.lastname: Parracho
authors.forename: P
authors.initials: P
authors.lastname: Pillot
authors.forename: T
authors.initials: T
authors.lastname: Poghosyan
authors.forename: G
authors.initials: G
authors.lastname: Puddu
authors.forename: E
authors.initials: E
authors.lastname: Radermacher
authors.forename: P
authors.initials: P
authors.lastname: Ramalhete
authors.forename: P
authors.initials: P
authors.lastname: Rosinsky
authors.forename: E
authors.initials: E
authors.lastname: Scomparin
authors.forename: J
authors.initials: J
authors.lastname: Seixas
authors.forename: S
authors.initials: S
authors.lastname: Serci
authors.forename: R
authors.initials: R
authors.lastname: Shahoyan
authors.forename: P
authors.initials: P
authors.lastname: Sonderegger
authors.forename: H J
authors.initials: HJ
authors.lastname: Specht
authors.forename: R
authors.initials: R
authors.lastname: Tieulent
authors.forename: G
authors.initials: G
authors.lastname: Usai
authors.forename: R
authors.initials: R
authors.lastname: Veenhof
authors.forename: H K
authors.initials: HK
authors.lastname: Wöhri