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

Abstract

Minijet production in $\sqrt{s} = 5.5$ 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 $\Upsilon$ family. We demonstrate that $p_T$-dependence of the $\Upsilon'/\Upsilon$ 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 $p_T$ spectra of the $\Upsilon$ resonances themselves will provide valuable information by comparing these spectra to that of the $Z$ boson, which should not be influenced by plasma production.