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@article{neg_c5_c6, title={Hyper-order baryon number fluctuations at finite temperature and density}, volume={104}, DOI={10.1103/physrevd.104.094047}, number={9 094047}, journal={Physical Review D}, author={Fu, Wei-jie and Luo, Xiaofeng and Pawlowski, Jan M. and Rennecke, Fabian and Wen, Rui and Yin, Shi}, year={2021}}
@article{cumulant_order, title={Skewness, kurtosis, and the fifth and sixth order cumulants of net baryon-number distributions from lattice QCD confront high-statistics star data}, volume={101}, DOI={10.1103/physrevd.101.074502}, number={7 074502}, journal={Physical Review D}, author={Bazavov, A. and Bollweg, D. and Ding, H.-T. and Enns, P. and Goswami, J. and Hegde, P. and Kaczmarek, O. and Karsch, F. and Larsen, R. and Mukherjee, Swagato and et al.}, year={2020}}
@article{bzdak_koch_2019, title={Mapping the QCD phase diagram with statistics-friendly distributions}, volume={100}, DOI={10.1103/physrevc.100.051902}, number={5 051902}, journal={Physical Review C}, author={Bzdak, Adam and Koch, Volker}, year={2019}}
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\title{Probing the nature of the QCD phase transition with higher-order net-proton number fluctuation and local parton density fluctuation measurements at RHIC-STAR}
\author{Dylan Neff and Ashish Pandav\\(for the STAR Collaboration)}
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Higher-order cumulants ($C_n$) of net-baryon distributions are sensitive to the nature of the QCD phase transition. Recent lattice QCD calculations~\cite{neg_c5_c6} suggest a negative $C_5/C_1$ and $C_6/C_2$ in the crossover regime at small baryon chemical potential ($\mu_B \leq$ 110 MeV). In addition, lattice QCD predicts a special ordering of cumulant ratios for systems of thermalized QGP~\cite{cumulant_order}: $C_3/C_1 > C_4/C_2 > C_5/C_1 > C_6/C_2$. Both predictions can be tested in heavy-ion collision experiments by measuring higher-order cumulants of the net-proton multiplicity distributions.

In the high $\mu_B$ region of the QCD phase diagram, proton multiplicity distributions are utilized to probe characteristics of the phase transition. The variance of proton multiplicity within azimuthal subvolumes of phase space may provide insight into local parton density fluctuations. The deviation of this variance from a binomial baseline along with proton factorial cumulants over the full azimuth~\cite{bzdak_koch_2019} may be observables sensitive to a possible first-order phase transition. 

In this talk, we report measurements of net-proton $C_5/C_1$ and $C_6/C_2$ in Au+Au collisions with center-of-mass energies from 3 GeV to 200 GeV, where the 3 GeV data are from the fixed-target program and the other data sets are from the Beam Energy Scan program phase I at RHIC-STAR. Proton factorial cumulants and the variance of proton multiplicities in azimuthal partitions are also presented. The cumulant measurements are compared with a QCD-based FRG model, UrQMD, and HRG calculations as well as lattice QCD calculations. The AMPT and MUSIC+FIST models are used as non-critical references in the search for local density fluctuations.


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