Conserved Charge Fluctuations and Correlations from Lattice QCD and the Beam Energy Scan

Transcription

1 Conserved Charge Fluctuations and Correlations from Lattice QCD and the Beam Energy Scan Frithjof Karsch Brookhaven National Laboratory & Bielefeld University Bielefeld-BNL-CCNU Collaboration A. Bazavov, H.-T. Ding, P. Hegde, O. Kaczmarek, FK, E. Laermann, S. Mukherjee, H. Ohno, P. Petreczky, C.Schmidt, S. Sharma, W. Soeldner and M.Wagner, arxiv: and preliminary results 1

2 Conserved Charge Fluctuations and Correlations from Lattice QCD and the Beam Energy Scan Frithjof Karsch Brookhaven National Laboratory & Bielefeld University Conclusion the preliminary STAR data on cumulant ratios of net-proton number distributions for can be understood in terms of a next-to-leading order expansion of net-baryon number fluctuations calculated in QCD equilibrium thermodynamics Bielefeld-BNL-CCNU Collaboration A. Bazavov, H.-T. Ding, P. Hegde, O. Kaczmarek, FK, E. Laermann, S. Mukherjee, H. Ohno, P. Petreczky, C.Schmidt, S. Sharma, W. Soeldner and M.Wagner, arxiv: and preliminary results 2

3 Exploring the QCD phase diagram X. Luo (STAR Collaboration), PoS CPOD2014 (2014) 019 equilibrium thermodynamics: Where is the critical point? conserved charge fluctuation controlled by 3

4 Exploring the QCD phase diagram More moderate questions: Can we understand the systematics seen in cumulants of charge fluctuations in terms of QCD thermodynamics? How far do we get with low order Taylor expansions of QCD in explaining the obvious deviations from HRG model behavior? equilibrium thermodynamics: Where is the critical point? conserved charge fluctuation controlled by 4

5 Exploring the QCD phase diagram More moderate questions: preliminary answer (modulo well known details like proton vs baryon fluctuations, acceptance cuts,.)? equilibrium thermodynamics: For Structure of net-electric charge and net-proton cumulants is inconsistent with HRG thermodynamics, but can eventually be understood in terms of QCD thermodynamics in a next-to-leading order Taylor expansion Where is the critical point? conserved charge fluctuation controlled by 5

6 STAR and PHENIX data on cumulant ratios of net-proton number and net-electric charge fluctuations 6

7 STAR and PHENIX data on cumulant ratios of net-proton number and net-electric charge fluctuations and are monotonic functions of and hence also of (this is not trivial; It will not hold close to a critical point!) replace in favor of, e.g., e.g. 7

8 Taylor expansion of the pressure generalized susceptibilities: conserved charge fluctuations: 8

9 Conserved charge fluctuations and freeze-out mean and variance for simplicity: e.g. ratio of cumulants on ''a line'' in the plane (NLO Taylor expansion) will not discuss here: non-equilibrium effects (see Swagato's talk) (S. Mukherjee et al., arxiv: ) proton vs. baryon number distributions (M. Kitazawa et al, arxiv: , arxiv: ) acceptance and pt-cuts (P. Garg et al, arxiv: , FK et al, arxiv: A. Bzdak and V. Koch, arxiv: ) 9

10 Conserved charge fluctuations and freeze-out mean and variance for simplicity: ratio of cumulants on ''a line'' in the plane (NLO Taylor expansion) 10

11 Conserved charge fluctuations and freeze-out mean and variance for simplicity: freeze-out line ratio of cumulants on ''a line'' in the plane (NLO Taylor expansion) all eventually need to be expanded in T 11

12 Conserved charge fluctuations and freeze-out mean and variance for simplicity: freeze-out line ratio of cumulants on ''a line'' in the plane (NLO Taylor expansion) cumulant ratios on the freeze-out line all eventually need to be expanded in T 12

13 Curvature of the freeze-out line compare lattice QCD calculation of with experimental data for BI-BNL-CCNU, arxiv:1509:05786 intercept fixes freeze-out temperature slope fixes curvature coefficient 13

14 Curvature of the freeze-out line compare lattice QCD calculation of with experimental data for BI-BNL-CCNU, arxiv:1509:05786 fits to data yield comparing intercept with yields once 155 MeV 147 MeV 145 MeV is fixed, the coefficients and are fixed and the slope of the data determines 14

15 Curvature of the freeze-out line compare lattice QCD calculation of fits to data yield with experimental data for BI-BNL-CCNU, arxiv:1509:05786 published STAR data are too steep, yield a negative curvature 155 MeV 147 MeV 145 MeV prelim. STAR data favor a small curvature coefficient for the freeze-out curve 15

16 Conserved charge fluctuations and freeze-out mean, variance and skewness huge deviations from HRG at all do we understand this in QCD? NLO Taylor expansion What does the curvature tell us? for simplicity: 16

17 Conserved charge fluctuations and freeze-out mean, variance and skewness NLO Taylor expansion used determined from fit to 17

18 Conserved charge fluctuations and freeze-out mean, variance and skewness NLO Taylor expansion used determined from fit to 18

19 Conserved charge fluctuations and freeze-out mean, variance and skewness NLO Taylor expansion curvature is negative 19

20 Conserved charge fluctuations and freeze-out mean, variance and skewness NLO Taylor expansion used determined from fit to 20

21 Conserved charge fluctuations and freeze-out mean, variance, skewness and kurtosis in a NLO Taylor expansion are closely related data at present without errors 21

22 Conserved charge fluctuations and freeze-out mean, variance, skewness and kurtosis in a NLO Taylor expansion are closely related 22

23 Conclusion a comparison of the STAR data on net-proton number fluctuations with QCD thermodynamics suggests curvature of the freeze-out line is compatible with zero the freeze-out temperature is below that for the crossover transition the kurtosis ratio is smaller than the skewness ratio 23

24 Conclusion the preliminary STAR data on mean and variance of net-proton number distributions can be understood in terms of a next-to-leading order expansion of net-baryon number and net-electric charge fluctuations calculated in QCD equilibrium thermodynamics 24