PUB - Publikationen an der Universität Bielefeld

Ratios of cumulants of conserved net charge fluctuations are sensitive to thedegrees of freedom that are carriers of the corresponding quantum numbers indifferent phases of strong interaction matter. Using lattice QCD with 2+1dynamical flavors and quenched charm quarks we calculate second and fourthorder cumulants of net charm fluctuations and their correlations with otherconserved charges such as net baryon number, electric charge and strangeness.Analyzing appropriate ratios of these cumulants we probe the nature of charmeddegrees of freedom in the vicinity of the QCD chiral crossover region. We showthat for temperatures above the chiral crossover transition temperature,charmed degrees of freedom can no longer be described by an uncorrelated gas ofhadrons. This suggests that the dissociation of open charm hadrons and theemergence of deconfined charm states sets in just near the chiral crossovertransition. Till the crossover region we compare these lattice QCD results withtwo hadron resonance gas models --including only the experimentally establishedcharmed resonances and also including additional states predicted by quarkmodel and lattice QCD calculations. This comparison provides evidence for sofar unobserved charmed hadrons that contribute to the thermodynamics in thecrossover region.