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Terence J Tarnowsky (for the STAR Collaboration) Michigan State University

Searching for the QCD Critical Point Using Particle Ratio Fluctuations and Higher Moments of Multiplicity Distributions. Terence J Tarnowsky (for the STAR Collaboration) Michigan State University Quark Matter 2011, Annecy, France May 23, 2011. Outline. Introduction STAR Detector

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Terence J Tarnowsky (for the STAR Collaboration) Michigan State University

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  1. Searching for the QCD Critical Point Using Particle Ratio Fluctuations and Higher Moments of Multiplicity Distributions Terence J Tarnowsky (for the STAR Collaboration) Michigan State University Quark Matter 2011, Annecy, France May 23, 2011

  2. Outline • Introduction • STAR Detector • Particle Ratio Fluctuations • Higher moments of Conserved Quantities. • Summary Quark Matter 2011 May 23, 2011

  3. Motivation Behind Correlations and Fluctuations • Have been many theoretical predictions that the behavior of correlations and fluctuations in a deconfined phase are different than that in hadron gas. • Experimental justification from studies of the thermodynamics of phase transitions. • Even w/o such guidance, can search for discontinuities in fluctuations and correlations as functions of incident energy and centrality (not an inclusive list): • Particle ratio fluctuations (K/p, p/p, K/p). • Forward-Backward multiplicity correlations. • Balance Functions • Higher moments of conserved quantities. • Etc. See Posters: Lizhu Chen, Poster #146, Xiaofeng Luo, Poster #141, Nihar Sahoo, Poster #191, Amal Sarkar, Poster #93, Michael Skoby, Poster #89, Prithwish Tribedy, Poster #86, Hui Wang, Poster #95 Quark Matter 2011 May 23, 2011

  4. Search for the QCD Critical Point • In a phase transition near a critical point, an increase in non-statistical fluctuations is expected. • Finite system-size effects may influence fluctuation measurements. • Finite-size scaling of fluctuations may indicate existence of critical point. • E.g. Change in behavior of quark susceptibilities. Aoki, Endrodi, Fodor, Katz, and Szabó Nature443, 675-678 (2006) • These may manifest in final-state measurements. mB = 0 mB = 0 Quark Matter 2011 May 23, 2011

  5. RHIC “Energy Scan” • Using RHIC to run an “energy scan” to search for predicted QCD critical point. • For 2010, we had Au+Au collisions at √sNN = 200, 62.4, 39, 11.5, and 7.7 GeV. • 2011 added Au+Au collisions at √sNN = 19.6 GeV. • 2012 should bring Au+Au collisions √sNN = 27 GeV. • Can examine our fluctuation observables to look for non-monotonic behavior as a function of collision energy. Quark Matter 2011 May 23, 2011

  6. STAR Detector • STAR is a large acceptance detector. • Good h and j coverage for measuring fluctuations. • TPC: |h| < 1.0, TOF: |h| < 0.9 • TOF upgrade has enhanced STAR’s PID capabilities. Quark Matter 2011 May 23, 2011

  7. Particle Ratio Fluctuations p/p (p+ + p-)/(p+ + p-) K/p (K+ + K-)/(p+ + p-) K/p (K+ + K-)/(p+ + p-)

  8. Fluctuation Observables, sdyn • NA49 uses the variable dyn s is the reduced width of K/p distribution Quark Matter 2011 May 23, 2011

  9. Fluctuation Observables, ndyn • STAR uses a different fluctuation observable, ndyn. • Introduced to study net-charge fluctuations. • Measures deviation from Poisson behavior. • It has been demonstrated that, Quark Matter 2011 May 23, 2011

  10. Phys.Rev.Lett.103:092301,2009 Excitation Function for sdyn,K/p Large decrease in fluctuations as function of energy from NA49. Fluctuations measured by STAR approximately constant as function of energy from 19.6-200 GeV. |h| < 1.0 p, K: 0.2 < pT < 0.6 GeV/c. STAR central Au+Au (0-5%) collisions with SPS central Pb+Pb collisions (0-3.5%). Quark Matter 2011 May 23, 2011

  11. Excitation Function for ndyn,p/p • NA49 sdyn,p/p converted to ndyn,p/p. • TPC+TOF (GeV/c): • p : 0.2 < pT < 1.4 • p : 0.4 < pT < 1.8 • TPC+TOF includes statistical and systematic errors from electron contamination. • Agreement with measurements from NA49 at low energies. (NA49 data from: C. Alt et al. [NA49 Collab.], Phys. Rev. C 79, 044910 (2009) • UrQMD and HSD predictions both change sign at high energies. Quark Matter 2011 May 23, 2011

  12. Excitation Function for ndyn,K/p NA49 sdyn,K/p converted to ndyn,K/p using s2dyn = ndyn. • TPC+TOF (GeV/c): • K : 0.2 < pT < 1.4 • p : 0.4 < pT < 1.8 • TPC+TOF includes statistical and systematic errors from electron contamination. • Large deviation between STAR and NA49 result at √sNN = 7.7 GeV. (NA49 data from: T. Anticic, et al [NA49 Collab.] arXiv:1101.3250v1 [nucl-ex]) • Models predominantly independent of experimental acceptance. Quark Matter 2011 May 23, 2011

  13. Excitation Function for ndyn,K/p • TPC+TOF (GeV/c): • p : 0.2 < pT < 1.4 • K : 0.2 < pT < 1.4 • TPC+TOF includes statistical and systematic errors from electron contamination. • Pion contamination of kaons < 3% using TPC and TOF. • Difference between STAR and NA49 result below √sNN = 11.5 GeV. (NA49 data from C. Alt et al. [NA49 Collab.], Phys. Rev. C 79, 044910 (2009) • Both models show little acceptance effects. • UrQMD predicts little energy dependence. • HSD predicts an energy dependence. NA49 sdyn,K/p converted to ndyn,K/p using s2dyn = ndyn. Quark Matter 2011 May 23, 2011

  14. Higher Moments of Conserved Quantities (Skewness and kurtosis of net-protons and net-charge)

  15. 1st moment: mean = M 2nd moment: variance = s2 3rd standardized moment: skewness = S 4th standardized moment: kurtosis = k Calculate moments from the event-by-event net proton distribution. Have similar plots for net-charge and net-kaon distributions. Higher Moments of Net-Proton Distributions STAR Preliminary See Posters: Xiaofeng Luo, Poster #141, Nihar Sahoo, Poster #191, Amal Sarkar, Poster #93 Quark Matter 2011 May 23, 2011

  16. Connection to Physical Quantities • Higher moments of net-proton distribution can be related to thermodynamic susceptibilities. • (Ss)B = cB3 / cB2 • (ks2)B = cB4 / cB2 • (M.Cheng et al, Phys. Rev. D 79, 074505 (2009), F. Karsch and K. Redlich, Phys. Lett. B 695, 136 (2011)) • Predictions that critical fluctuations contribute to higher moments and are strongly dependent on correlation length (z) of the system: • 4th order moments go as z7. (M. A. Stephanov, Phys. Rev. Lett. 102, 032301 (2009)) • For net-charge, change index from B to Q. For net-kaons, change B to S. Quark Matter 2011 May 23, 2011

  17. Products of the moments cancel volume effects. Deviation from Hadron Resonance Gas (HRG) prediction below 62.4 GeV. For HRG: Ss = tanh(mB/T) ks2= 1 Products of the Moments See Xiaofeng Luo, Poster #141 Quark Matter 2011 May 23, 2011

  18. Products of the moments cancel volume effects. Products of the Moments See Nihar Sahoo, Poster #141 Quark Matter 2011 May 23, 2011

  19. Summary • New results for dynamical particle ratio fluctuations from data collected during first part of the RHIC energy scan to search for QCD critical point. • For p/p fluctuations: • From √sNN = 7.7-200 GeV, all measured fluctuations are negative. • For K/p fluctuations: • Similar to p/p, fluctuations measured from √sNN = 7.7-200 GeV are negative. • For K/p fluctuations: • STAR does not observe any strong energy dependence of K/p fluctuations in central Au+Au collisions. • Additional systematics under study. • An additional data point below √sNN = 7.7 GeV (e.g. √sNN = 5 GeV) could provide additional support to the observed trends. • Higher moments of the distributions of conserved quantities (e.g. net-proton, net-charge) are expected to be sensitive to critical fluctuations. • For net-proton, Ss and ks2 are consistent with the HRG prediction above √sNN = 39 GeV, but slightly below the prediction at lower energies. Quark Matter 2011 May 23, 2011

  20. BACKUP Quark Matter 2011 May 23, 2011

  21. STAR Fluctuation and Correlation Posters • Mix-Ratios of Higher Order Moments of Protons and Kaons for QCD Critical Point search at RHIC. (Lizhu Chen, Poster #146) • Higher Moments of Event-by-Event Net-proton Multiplicity Distributions at RHIC. (Xiaofeng Luo, Poster #141) • Search for the QCD Critical Point by the Higher Moments of the Net-charge Multiplicity Distribution. (Nihar Sahoo, Poster #191) • Net Kaon Fluctuations in the STAR Beam Energy Scan Program. (Amal Sarkar, Poster #93) • Forward-Backward Multiplicity Correlations for Identified Particles at STAR. (Michael Skoby, Poster #89) • Local Parity Violation or Local Charge Conservation/Flow? A Reaction-Plane-Dependent Balance Function Study. (Hui Wang, Poster #95) • Charge-to-Neutral Fluctuations in AuAu Collisions at Forward Rapidity at RHIC. (Prithwish Tribedy, Poster #86) Quark Matter 2011 May 23, 2011

  22. 7.7 GeV Hui Wang Quark Matter 2011 May 23, 2011 11/13/2014 22 Hui Wang

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