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Correlations and Fluctuations from the STAR Experiment

Correlations and Fluctuations from the STAR Experiment. Terence J Tarnowsky for the STAR Collaboration January 6, 2010 Winter Workshop on Nuclear Dynamics 2010 Ocho Rios, Jamaica. Motivation Behind Correlations and Fluctuations.

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Correlations and Fluctuations from the STAR Experiment

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  1. Correlations and Fluctuations from the STAR Experiment Terence J Tarnowsky for the STAR Collaboration January 6, 2010 Winter Workshop on Nuclear Dynamics 2010 Ocho Rios, Jamaica

  2. Motivation Behind Correlations and Fluctuations • Many theoretical predictions that behavior of correlations and fluctuations in a deconfined phase different than that in hadron gas. • Justification from experimental 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 • Net Charge Fluctuations • Net-proton kurtosis, <pT> flucuations, Dh-Dj correlations, etc. WWND 2010, Jamaica January 6, 2010

  3. STAR Detector • STAR is a large acceptance detector. • Good h and j coverage for measuring fluctuations. • |h| < 1.0 • PID: • p, K, p ID for pT < 1 GeV. • ToF upgrade will enhance PID capabilities. STAR Preliminary WWND 2010, Jamaica January 6, 2010

  4. F-B Multiplicity Correlations • Predicted in context of Dual Parton Model [DPM] (and ColorGlassCondensate [CGC]). • Test of multiple elementary [partonic] scattering. • Linear expression relating Nb and Nf (forward and backward multiplicity), found in hadron-hadron experiments (ex. UA5), • “b” is correlation strength. • Function of √s and A. • Coefficient can be expressed as, N = # of hadrons WWND 2010, Jamaica January 6, 2010

  5. Strings Low Energy Long Range Long Range Short + Long Range High Energy Backward nb Forward nf η - η1 η1 η2 - η2 0 Pseudorapidity Gap Probes longitudinalcharacteristics of the system. WWND 2010, Jamaica January 6, 2010 Pseudorapidity interval

  6. F-B Correlations Central 200 GeV Au+Au collisions show a strong long-range correlation. Most peripheral Au+Au have negligible LRC, as does pp. HIJING and Parton String Model (PSM) do not agree w/ Au+Au data. Multiparton interaction in central Au+Au collisions. See talk by M. Skoby. Phys.Rev.Lett.103:172301,2009 WWND 2010, Jamaica January 6, 2010

  7. Characterize Fluctuations • NA49 uses the variable dyn • Measure deviation from Poisson behavior using dyn • It has been demonstrated (for K/p and p/p) that, WWND 2010, Jamaica January 6, 2010

  8. Excitation Function for σdyn,K/π Phys.Rev.Lett.103:092301,2009 • 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. • p : 0.2 < pT < 0.6 GeV/c • K: 0.2 < pT < 0.6 GeV/c STAR central Au+Au (0-5%) collisions with SPS central Pb+Pb collisions (0-3.5%). WWND 2010, Jamaica January 6, 2010

  9. Phys.Rev.Lett.103:092301,2009 Scaling w/ dN/dh in Au+Au Charge dependent and independent ndyn,K/p was found to scale linearly with dN/dh (at small dn/dh) in Au+Au at 200 and 62.4 GeV WWND 2010, Jamaica January 6, 2010

  10. Excitation Function for σdyn,pπ Solid points are data from STAR or NA49. Open black points are HSD prediction from Konchakovski, et. al. arXiv:0906.3229. Open red points are UrQMD run locally with STAR acceptance.

  11. ndyn,p/p, STAR and NA49 ndyn,p/pdisplays strong system size dependence for small dN/dh. Fit is to STAR Cu+Cu 22.4 GeV data only. Interpretation still under study. WWND 2010, Jamaica January 6, 2010

  12. Excitation Function for σdyn,Kp HSD points from arXiv:0906.3229 NA49 data from CPOD 2009 talk by T. Schuster • sdyn,K/p for central Cu+Cu 22.4 GeV is strongly negative. • General agreement w/ NA49 at 17.3 GeV. • Does not show large increase seen in model predictions. • sdyn,K/p for central Au+Au 200 and 62.4 GeV are also negative. WWND 2010, Jamaica January 6, 2010

  13. Balance Function • Prediction that delayed hadronization will cause width of longitudinal charge balance function to be narrower in central vs. peripheral collisions. • Definition: • Dij is number of charged particles pairs in a (pseudo)rapidity range. • Calculated by taking ith particle and incrementing a histogram of Dh wrt all jth particles in that event. WWND 2010, Jamaica January 6, 2010

  14. Balance Function • Width in 200 GeV Au+Au data narrows with increasing collision centrality. • Shuffled events and Hijing and URQMD show no centrality dependence. • Width from pp collisions agrees w/ most peripheral Au+Au bin. • Results consistent with narrowing of the balance function in most central Au+Au collisions. STAR Preliminary STAR Preliminary WWND 2010, Jamaica January 6, 2010

  15. Net Charge Fluctuations • Predictions that net charge fluctuations due to QGP << Hadron Gas. • Measured using, WWND 2010, Jamaica January 6, 2010

  16. Net Charge Fluctuations • Large differences between pp, Cu+Cu, and Au+Au. Slope depends on correlation length in h. Larger slope = shorter correlation length. Agrees w/ balance function results. • Larger slope indicate correlated pairs of -/+ particles emitted closer in rapidity than those in peripheral Au+Au or pp collisions. • Could be related to narrowing of balance function, or radial flow. Phys. Rev. C 79 (2009) 24906 WWND 2010, Jamaica January 6, 2010

  17. Search for the QCD Critical Point Proposal for future running at RHIC to consist of an “energy scan” to search for predicted QCD critical point. Fluctuations and correlations (particle ratios, multiplicity, pT, etc.) and behavior of flow (directed and elliptic) in vicinity of the critical point are expected to be primary signatures. STAR has the capability to measure correlations and fluctuations at all energies. WWND 2010, Jamaica January 6, 2010

  18. 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. Search for the QCD Critical Point II WWND 2010, Jamaica January 6, 2010

  19. Critical Fluctuations • An example of critical fluctuations: • Mixture of cyclohexane (C6H12) and aniline (C6H7N). WWND 2010, Jamaica January 6, 2010

  20. 2008 Test at √sNN =9.2 GeV WWND 2010, Jamaica January 6, 2010

  21. STAR • The STAR detector is in a prime configuration for measuring fluctuations and correlations: • Full ToF is installed. Will provide enhanced PID capabilities. • Low material budget between beam pipe and TPC. • DAQ 1000 installed as of Run 9. Not rate limited by DAQ at higher energies of BES. WWND 2010, Jamaica January 6, 2010

  22. Summary • The STAR experiment has results on fluctuations and correlations for several colliding systems and energies that have provided new insights into particle production. • K/p fluctuations approximately constant at RHIC energies. • First measurement of long-range forward-backward multiplicity correlations provides information on multiparton interactions. • Narrowing of balance function coincides with shorter correlation lengths as measured from net charge fluctuations. • The RHIC Beam Energy Scan (BES) program will probe new areas of the QCD phase diagram while revisiting energies studied at fixed target experiments using a mature collider and well understood detector setup. • Provide a comprehensive picture of the T-mB phase space at the same facility. • The STAR experiment is fully prepared to capitalize on collisions at all energies during the RHIC BES. • STAR will continue to produce new results in the future from higher statistics data sets w/ the Time-of-Flight upgrade. WWND 2010, Jamaica January 6, 2010

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