Higher-order cumulants of conserved quantities (B, Q, S) are sensitive observables to study the QCD phase structures, nature of quark-hadron phase transition and freeze-out dynamics.
In this talk, we will present new measurements of sixth to second-order cumulant ratios (C6/C2) of net-proton distributions in Au+Au collisions at sNN =54.4 and 200 GeV, as well as cumulants up to the fourth-order of net-proton, net-kaon and net-charge multiplicity distributions in Au+Au collisions at sNN =27 and 54.4 GeV. The C6/C2 results are compared with a recent model calculation which predicts a negative C6/C2 value if the freeze-out occurs 10 near the chiral transition temperature. The dependence of cumulants, measured in Au+Au collisions at sNN =27 GeV, on the centrality definition was tested using the Event Plane Detector (EPD). The physics implications of the results, a detailed discussion of the background contributions and the status and prospects of phase II of the STAR Beam Energy Scan program are discussed.