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Claude A Pruneau STAR Collaboration Physics & Astronomy Department Wayne State University

2nd International Workshop on the Critical Point and Onset of Deconfinement, 2005 Bergen, Norway Fluctuations at RHIC. Claude A Pruneau STAR Collaboration Physics & Astronomy Department Wayne State University Detroit, Michigan, USA. Talk Outline. Net Charge Fluctuations

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Claude A Pruneau STAR Collaboration Physics & Astronomy Department Wayne State University

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  1. 2nd International Workshop on the Critical Point and Onset of Deconfinement, 2005Bergen, NorwayFluctuations at RHIC Claude A Pruneau STAR Collaboration Physics & Astronomy Department Wayne State University Detroit, Michigan, USA

  2. Talk Outline • Net Charge Fluctuations • Transverse Momentum Fluctuations • K/ Fluctuations (proof of principle) • Questions: • Smoking gun for QGP, phase transition ? • Can we learn about the collision dynamics ?

  3. Net Charge Fluctuations - a signature for the QGP ? Prediction by Koch, Jeon, et al., Asakawa et al., Heiselberg et al., of reduced net charge fluctuation variance following the production of a QGP.

  4. Predictions Consider different scenarios: Neutral resonances decay to charged particles • Increases Nch • Do not contribute to <DQ2> Jeon/Koch, PRL83(99)5435 QGP QGP - Coalescence Scenario (A. Bialas, PLB 532 (2002) 249) Gluons “attached” to quarks and forming constituent quarks. Small contribution to the entropy.

  5. Brief Historical Review • Choice of Observable • Many different approaches proposed/used • “D” - S. Jeon and V. Koch, Phys. Rev. Lett. 85, 2076 “Q” - H. Heiselberg, Phys. Rep. 351, 161 • “ Q” - M. Gazdzicki and S. Mrowczynski, Z. Phys. C 54, 127 “+-,dyn” - C.P., S. Gavin, S. Voloshin - PRC 66, 44904 (2002). • Relationships between observables • S. Mrowczynski, nucl-th/0112007. • “Equivalence not perfect - advocate usage a common language by all experiments. • Published Measurements • Au + Au sNN1/2 = 130 GeV • PHENIX, PRL 89 (2002) 082301. • STAR, PRC68, 044905 (2003). • Pb + Pb • CERES @ QM04 • NA49

  6. Dynamical Net Charge Fluctuations Independent Particle (Poisson) Limit Definition: Measurement: Physical Motivation: Properties and robustness of this observable discussed in: “Methods for the study of particle production fluctuations”, C.P., S.G., S.V. - PRC 66, 44904 (2002). S. Mrowczynski, PRC C66, 024904 (2002). “On the Net-Charge Fluctuations in Relativistic Heavy-Ion Interactions”, J. Nystrand, E. Stenlund, and H. Tydesjo, PRC 68, 034902 (2003).

  7. Dynamical Fluctuations Properties Independent of volumefluctuationsIndependent Particle Production Collision Dynamics Independent of collisioncentrality Robust Observable(Independent of efficiency) Charge Conservation Perfect N+=N- correlation

  8. Data Sets - STAR • Au + Au • sNN1/2 = 20, 62, 130, 200 GeV • Collision Centrality Determination based on all charged particle multiplicity ||<0.5. • Centrality slices 0-5%, 5-10%, 10-20 %, … • Use Glauber model/MC to estimate the corresponding number of participants. • Events analyzed for |zvertex|<MAX. • DCA < 3 cm. • Track quality Nhit>15; Nfit/Nhit>0.5. • Fluctuations studied in finite rapidity ranges, and azimuthal slices, for 0.2 < pt < 5.0 GeV/c.

  9. Net Charge Dynamical Fluctuations Beam Energy Dependence Study STAR TPC - ||<0.5; 0.2 < pt < 5.0 GeV/c Au +Au • Finite Fluctuations • @ all energies. • Increased dilution with increasing Npart • Some energy dependence • |n+-,dyn| larger at 20 than 62, 130 and 200 GeV.

  10. Effects of Kinematic Cut Simulation based on 630k HIJING events @ 62 GeV ||<0.6, pt>0., 0.1, 0.2, 0.3 GeV/c

  11. Comparisons with Models 1000000/620000 Hijing events, 700000 RQMD events

  12. Au +Au 62 GeV QGP Signature? 1/N Scaling? PHOBOS - PRC65, 061901R Au + Au sqrt(sNN)=130 and 200 GeV. Poisson Limit Coalescence Resonance Gas Koch/Jeon QGP ~ -3.

  13. Fluctuations vs Beam Energy STAR -Preliminary H. Sako (CERES) @ QM 04. Not corrected for finite efficiency

  14. Dynamical Fluctuations vs Energy STAR ||<0.5 PHENIX ||<0.35, =/2 CERES 2.0<  <2.9 UrQMD RQMD

  15. NA49 Results

  16. Summary so far… • No smoking gun for D ~ 1 • +-,dyn dependence on beam energy is not clear. • dN/d+-,dyn exhibits finite dependence on beam energy and collision centrality - mostly accounted for by the change in dN/d. • More detailed comparison between experiments requires more work… • What about reaction dynamic effects?

  17. Transverse Momentum Fluctuations • Pt Dynamic Fluctuations observed to be finite at RHIC. • PHENIX • STAR • Non-monotonic change in pt correlations with incident energy/centrality might indicate the onset of QGP. • STAR - Au + Au sNN1/2 = 20, 62, 130, 200 GeV. • ||<1, 0.15 < pt < 2.0 GeV/c

  18. Measurement of Pt Fluctuations • To quantify dynamical pt fluctuations • We define the quantity <pt,1pt,2>. • It is a covariance and an integral of 2-body correlations. • It equals zero in the absence of dynamical fluctuations • Defined to be positive for correlation and negative for anti-correlation.

  19. Pt Correlation Integral G. Westfall et al., STAR to be submitted to PRC. • Calculate <<pt>> and <pt,1pt,2> • Vs acceptance • Vs centrality - 9 standard STAR centrality bins in Nch, || < 0.5 • Results reported here for all centralities for || < 1.0 (full STAR acceptance) for 0.15 < pt < 2.0 GeV/c • Correlations are positive • Decrease with centrality • ~ 1/N dependence • Somee incident energy dependence • HIJING underpredicts the measured correlations

  20. Scaling Properties (1) Scale <pt,1pt,2> by dN/dto remove 1/N correlation dilutionand allow comparison with pt and pt Clear Scaling Violation HIJING does not agree with the data. - Magnitude - Centrality Dependence

  21. Scaling Properties (2) Take square root of <pt,1pt,2>, divide by <<pt>> to obtain dimensionless quantity + remove effects of <<pt>> variation incident energy and centrality HIJING still does not agree with the data. CERES - SPS - Adamova et al., Nucl. Phys. A727, 97 (2003)

  22. 1.1% (<pt,ipt,j>)1/2/<<pt>>

  23. Dynamical Effects • Resonance Decays • Radial and Elliptical Flow • Diffusion/Thermalization • Jet Production/Quenching • …

  24.  ~ 0.17 kos~ 0.12 ~ 0.08 effective with DCA < 3cm. Resonances  0.3 STAR, PRL92 (2004) 092301 Resonance Contributions - An Example Assume multinomial production of p+, p-, and ro with probabilities f1, f2, and f3. Generating functions: n+-,dyn Probability - f3

  25. Collectivity S. Voloshin, nucl-th/0312065 Uses “blast wave” Model

  26. Sensitivity to Velocity Profile S. Voloshin, nucl-th/0312065 Single Particle Spectrum Two Particle Correlation

  27. Comparison with Data Scale <pt,1pt,2>, divide by <<pt>>2 and number of participants. Compare to Blastwave calculation by S. Voloshin

  28. Effect of radial flow on Net Charge Correlations Toy model Multinomial production of +, -, and 0. Isotropic source Maxwell Boltzman Dist. T = 0.18 GeV Radial Flow vr as shown.

  29. Toy Model (Continued) Binomial production of +, -, and X0. Isotropic source Maxwell Boltzman Dist. T = 0.18 GeV No Radial Flow mx as shown.

  30. Hijing/Rqmd Prediction of Angular Dependence Au + Au @ sNN1/2 = 62 GeV RQMD HIJING Version 1.38

  31. STAR @ 200 GeV RQMD +-,dyn vs || range

  32. 0-5% 10-20% 30-40% 70-80% Azimuthal Dependence Au+Au @ sNN1/2 = 62 GeV Resonance Gas - Toy Model T=0.18 GeV; +, -, , K0s, vr as shown Indications of resonance + flow effects Interpretation requires detailed model comparisons

  33. K/ Fluctuation Measurement Consider two approaches: Fluctuations of the Kaon to Pion yields ratios Measure integral correlations Particle identification from dE/dx in TPC M. Anderson et al. NIMA499 (2003)

  34. K/ Fluctuations Preliminary Suprya Das, STAR

  35. HIJING 1.38 - Au + Au 200 GeV k,dyn(||<0.5) k,dyn M K/ Dynamical Fluctuations Preliminary

  36. Summary • Net Charge fluctuations • No smoking gun for reduced fluctuations as predicted by Koch et al. • Bulk of observed correlations due to resonance decays. • A new tool to evaluate the role of resonances and radial flow. • Observed centrality dependence of +-,dyn vs . • Pt fluctuations • No smoking gun for large fluctuations. • No beam energy dependence. • A tool to study the velocity profile (see Sergei Voloshin’s talk). • K/ Yield fluctuations • Results by STAR on their way...

  37. Energy Dependence Au + Au 0-5 % most central collisions Charge Conservation Limit: n+-,q-lim = -4/NCH,4p

  38. Comparison with HIJING/RQMD

  39. Thermalization S. Gavin, Nucl. Dyn. Conf. Jamaica • Solves Boltzmann equation with Langevin noise • phase-space correlations • dynamic fluctuations

  40. Summary of Charge Fluctuation Measuresbased on a slide from J. Mitchell’s QM04 talk.

  41. Basic Observable - Mixed Events • Au+Au at 200 GeV <pt,ipt,j> is zero for mixed events

  42. Estimate Contribution from Short Range Correlations • To get an estimate for the contribution from short range correlations, we calculate <pt,ipt,j> excluding pairs with qinv < 100 MeV • To do this calculation, we assume all particles are pions • model dependent • CERES carried out somewhat different calculation to estimate the contribution from SRC • When pairs with qinv < 100 MeV are removed, a strong, artificial anti-correlation is introduced • CERES compensated for this effect by introducing randomly chosen particles • We compensate by subtracting mixed events with the same cut on pairs with qinv < 100 MeV

  43. Results for SRC Estimation <pt,ipt,j>, qinv > 100 MeV Correlation Function Au+Au 62 GeV

  44. Au+Au 62 GeV Ratios<pt,ipt,j> for pairs with qinv > 100 MeVto <pt,ipt,j> for all pairs <Ratio> = 0.90  0.01 <Ratio> = 0.80  0.06 <Ratio> = 0.90  0.01 <Ratio> = 0.90  0.04

  45. Estimate of Contributionfrom SRC to <pt,ipt,j>

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