Measurement of the cumulants of net-proton multiplicity distributions by STAR

Fluctuations and correlations of conserved quantities (baryon number, strangeness, and charge) can be used to probe phases of the strongly interacting QCD matter and the possible existence of a critical point in the phase diagram. The cumulants of the multiplicity distributions related to these conserved quantities are expected to be sensitive to possible increased fluctuations near a critical point. In this report, we present the measurements of the cumulants of net-proton multiplicity distributions from Au+Au collisions at s_NN = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 (up to fourth order) and 200 GeV (up to sixth order) as measured by the STAR experiment at RHIC. Multi-particle correlation functions will also be presented. The higher order cumulants are also very sensitive to experimental artifacts that one has to deal with in the analyses of heavy-ion collision data. We demonstrate a data-driven approach to measure the cumulants of event-by-event distributions of physical variables using large samples of AMPT events. Our approach investigates the corrections for multiplicity-dependent detector response and efficiency variations. The comparison of the various correction approaches should provide important guidance towards a reliable experimental determination of the multiplicity cumulants.