Spatial correlations of charm and anticharm quarks at hadronisation

Abstract

Heavy-ion collisions are a unique tool for studying properties of strong interactions at high energy densities. In particular, the momentum correlations of charm and bottom hadrons have been considered for testing heavy quark thermalisation in the dense matter produced by the collisions. In this respect, two effects have been considered: the decrease of the initial back-to-back correlations and the increase of correlations due to heavy-quark interactions with the collectively flowing medium. Here, we show that information on the spatial correlations of the charm-anticharm quarks at the hadronisation can be extracted by measuring the momentum correlation of charm and anticharm hadrons produced in central collisions of two heavy nuclei. This, however, requires collisions with a single charm-anticharm quark pair created - the condition likely to be fulfilled in central Pb+Pb collisions at the CERN SPS energies. We introduce a method to correct the measured joint distribution function for the smearing of the charm and anticharm hadron momenta caused by hadronisation. Then the results are directly sensitive to the spatial correlations at the hadronisation. Using an example of central Pb+Pb collisions at the CERN SPS energies, we demonstrate that even a limited statistics of charm-anticharm hadron pairs can distinguish between different spatial correlation functions of charm-anticharm quarks at hadronisation. The results on spatial charm-anticharm quark correlations will provide a unique test of different assumptions on heavy quark creation in space-time and transport in dense, strongly interacting matter. We show that the existing detector technology and beam intensities at the CERN SPS should allow us to conduct the needed experiments soon.