Determining the existence and nature of the quark-gluon plasma by Upsilon suppression at the LHC

Minijet production in √ s = 5.5 TeV Pb+Pb collisions at the LHC is expected to produce a gluon-dominated plasma with large initial temperatures and energy densities. We discuss the implications of the high initial temperatures on the screening mass and on the relative suppression of members of the Υ family. We demonstrate that pT -dependence of the Υ /Υ ratio is only expected if a quark-gluon plasma with significant energy density is present, and that the precise dependence of this ratio will strongly constrain the QGP models. We also propose that the pT spectra of the Υ resonances themselves will provide valuable information by comparing these spectra to that of the Z boson, which should not be influenced by plasma production. Supported by the Department of Energy under Contract No. DE-FG03-91ER40674 and by the Davis Institute for High Energy Physics. This work was supported in part by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U. S. Department of Energy under Contract No. DE-AC03-76SF0098.