1. SPS Charm(onium) and Bottom(onium) measurements
E. Scomparin
INFN Torino (Italy)
Via P. Giuria 1, I Torino (Italy)
Abstract
Heavy quark and quarkonium production are an essential part of the heavy-ion program
at SPS energy. In particular, quarkonium production has been studied by NA38, NA50 and,
more recently, by the NA60 experiment. The results show that in both In-In and Pb-Pb
collisions an anomalous J/ suppression is present, i.e. suppression mechanisms different
from nuclear absorption must be invoked to explain the observed J/ yield. The onset of the
anomalous suppression occurs at around Npart=100. From the comparison of the centrality
pattern of the J/ suppression bewtween various systems, one can possibly single out the physics
variable, related to centrality, that drives the J/ suppression.
A first study of open charm production, triggered by the previous discovery (by Helios-3 and
NA38/NA50) of a dimuon excess in the intermediate mass region (m<mµµ<mJ/), has been
recently performed by NA60. Preliminary results show that, in In-In collisions, open charm
production scales, with respect to pp and pA, with the number of nucleon-nucleon collisions.
This result implies that the intermediate mass excess is not due to an anomalous open charm
enhancement, but rather to a “prompt” source. Further work, by theory and experiment,
is needed in order to understand if thermal dimuon production can account for the observed
excess.