Energy scan by ϕ mesons and threshold energy for the confinement–deconfinement phase transition

Abstract

We argue that the ratio of φ mesons multiplicity over cube of the mean pT is proportional to the degeneracy of the medium produced in ultra-relativistic heavy ion collisions. The ratio extracted from the existing φ meson data in the energy range √ s=6.3-200 GeV, indicate that beyond a threshold energy √ s th = 15.74 ± 8.10 GeV, the medium crosses over from a confined phase to a deconfined phase.PACS numbers: 25.75.Nq, 25.75.Ag Lattice QCD predicts [1,2] that in ultra-relativistic heavy ion collisions, a confinement-deconfinement phase transition can occur, producing a new state of matter, Quark-Gluon Plasma (QGP). QGP is a collective state where color degrees of freedom become manifest over nuclear rather than hadronic volume. Recent experiments [3-6] have produced convincing evidences for a confinement-deconfinement phase transition in √ s=200 GeV Au+Au collisions at RHIC. One naturally wonders, whether or not there is a threshold energy for the transition. One of the aims of the STAR's energy scan programme at RHIC is to determine the threshold energy for the confinement-deconfinement transition [7,8]. STAR proposes to study nuclear collisions at √ s=5, 7.7, 11.5, 17.3, 27 and 39 GeV. With the existing data at √ s=62,130 and 200 GeV, STAR will scan a large energy range, √ s=5-200 GeV. For long, strangeness enhancement is considered as a signature of QGP formation [9]. In QGP environment, gg → ss is abundant. If not annihilated before hadronisation, early produced strange and anti-strange quarks will coalesce in to form strange hadrons and compared to elementary pp collisions, strange particle production will be enhanced. However, strangeness enhancement could also be obtained in a purely hadronic scenario, mainly due to the 'volume effect' [10][11][12][13]. Strangeness production in small volume elementary pp collisions can be 'canonically' suppressed due to 'strict' strangeness conservation [10][11][12][13]. In bigger volume AA collisions, locally, strangeness conservation condition can be relaxed to produce strange particles. In the language of statistical mechanics, while canonical ensemble is applicable in pp collisions, grand canonical ensemble is more appropriate in heavy ion collisions. Additionally, strange particle phase space appears to be under-saturated in elementary pp or peripheral heavy ion collisions [14,15].As noted in [16], several unique features of φ mesons make it an ideal probe to investigate medium properties in heavy ion collisions. They are hidden strange particle and are not affected by canonical suppression. Also they *

Stopping in central Pb+Pb collisions at SPS energies and beyond

“…(a) E-mail: wolschin@uni-hd.de For φ-meson production, data from NA49 and STAR exist already for central Cu + Cu, Au + Au and Pb + Pb collisions in the energy range 6.3-200 GeV. It was argued in [6] that these data "indicate a threshold energy for the confinement-deconfinement phase transition" at √ s NN = 15.7 ± 8.1 GeV.…”