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Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS Energy

Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS Energy. … and their scale dependence in Dh-Df space. Georgios Tsiledakis for the CERES Collaboration GSI, Darmstadt, Germany. 2005 RHIC & AGS Annual Users' Meeting Tuesday, June 21, 2005. Outline.

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Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS Energy

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  1. Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS Energy • … and their scale dependence in Dh-Df space Georgios Tsiledakis for the CERES Collaboration GSI, Darmstadt, Germany 2005 RHIC & AGS Annual Users' Meeting Tuesday, June 21, 2005

  2. Outline • <pT> Fluctuations: Probing for Signs of a Phase Transition • CERES experiment at the SPS • Measure of mean pt fluctuations • Previous results from SPS • Recent results from run2000 at 158AGeV/c Pb-Au • Scale dependence of the fluctuation strength as a function of Df and Dh • Two-particle correlation plots (cumulant pT variable c) • Centrality dependence • Conclusions and outlook

  3. <pT>EbE Fluctuations: Search for signatures of the QCD phase transition They might be sensitive to… • 1st order Phase Transition • Formation of QGP droplets • 2nd order phase transitions • Location of Critical Point of QCD phase diagram • Lattice QCD : There is a critical point...but uncertainty in location is large. M. Stephanov (hep-ph/0402115) • Experiments : Can contribute... • Observables : <pT>EbE fluctuations … but also to… • HBT and Coulomb correlations • Collective flow • Resonance decays • (Mini-) jet production • … S. Mrowczynski (Phys. Lett. B314 (1993) 118) M. Stephanov, et al. (Phys. Rev. Lett. 81 (1998) 4816)

  4. Event-by-event mean pT distributions(CERES collaboration, Nucl. Phys. A727(2003)97-119) Event-by-event MpT distributions in real events are slightly wider than those in mixed events • Evidence for the non-statistical (dynamical) mean pT fluctuations Real mixed Real /mixed 6.5% central, 2.2<h<2.7, 0.1<pT<1.5GeV/c

  5. CERES Experiment radial TPC track/momentum RICHes Silicon Drift Detectors Primary vertex Hadron measurement near mid-rapidity in Pb+Au collisions acceptance: 8 < q < 15 deg 2.2 < h < 2.7 Df=2p Multiplicity Counter RUN2000 : 30M Pb-Au events at 158 AGeV/c, 8 % centrality 3M Pb-Au events at 158 AGeV/c, 20 % centrality • 7M events analyzed for the present analysis

  6. Measure of mean pt fluctuations • DMpT : r.m.s. of MpT dist. • Dp2T : r.m.s. of inclusive pT dist. • <N> : mean multiplicity • pT : inclusive mean pT • normalizeddynamical fluctuation Dimensionless measure = 0 for purely statistical fluctuation > 0(< 0) with positive/negative two-particle correlation or dynamical EbyE fluctuation SpT • Proportional to mean covariance • of all particle pairs / event • Robust under change of multiplicity due to changes in beam energy and acceptance

  7. Previous results on Event-by-Event fluctuations of Mpt Collision energy dependence • Dynamical fluctuations of ~ 1 % are observed at SPS, which are similar to RHIC data. • No indication for the critical point or phase transition is observed. (CERES collaboration, Nucl. Phys. A727(2003)97, J.Phys.G30(2004)S1376)

  8. Centrality dependence • Baseline:extrapolation from p+p measurement 12% measured in p+p@ISR (Braune, PLB123(1983)467) • Non-monotonic dependence of NpartSpT2 • Little collision energy dependence • Maximum in semi-central events • Consistent with the p+p extrapolation in central and peripheral NpartSpT2= 0.03(const) (CERES collaboration, Nucl. Phys. A727(2003)97, J.Phys.G30(2004)S1376)

  9. Comparison to STAR and NA49 data STAR preliminary CERES NA49 (158AGeV/c) hep-ex/0311009 G. Westfall, QM2004 • Similar fluctuations at each centrality at SPS and RHIC energies similar non-monotonic dependence

  10. Rapidity range dependence of Mean pT fluctuations • Monotonic increase in FpT, decrease and saturation in SpT • SpT agrees at each Dh bin at 3 beam energies • We use SpT to compare data with different Dh FpT dependent on multiplicity, acceptance size, beam energy. (CERES collaboration, Nucl. Phys. A727(2003)97)

  11. Fpt measure at NA49 data • Proposed by S. Mrowczynski, and M. Gazdzicki. NA49 nucl-ex/0208020 Fpt small and charge dependent

  12. Recent results from run2000 at 158AGeV/c Pb-Au • Scale dependence of the fluctuation strength as a function of Df and Dh magnitude of fluctuations • Two-particle correlation plots (cumulant pT variable c) origin of fluctuations ??

  13. Tracking selection and parameters • Track Selection • TPC tracks (no. of hits >= 12 out of 20) • Target cut (projection of TPC track on the primary vertex < 10cm) • Momentum resolution Dp/p =((0.0152+(0.016p)2)1/ 2 at 158 AGeV • Full f Acceptance • Tracking efficiency • Better than 85% at pT>0.05GeV/c • 2-particle resolution • ~5 mrad in TPC • 7M events analyzed for the present analysis • 0.1 < pT < 1.5

  14. Centrality determination 50 40 30 20 10 5 0 % minb cental Centrality selection Multiplicity Counter (158 GeV) Number of participant nucleons is estimated with a geometric nuclear overlap (Glauber) model • 0%-100% of the total Pb+Au • inelastic cross section • 0% -> impact parameter=0 • Multiplicity Counter gain distribution

  15. Average momentum correlator <pt,i pt,j> S. Voloshin. V. Koch. H. Ritter, PRC60 (1999) mean covariance of all particle pairs / event … but <Dpt,iDpt,j> allows to select pairs by charge sign, Df, Dh,...

  16. Peaks at Df=0, Dh=0 and Dh=0, Df=p <Dpt,iDpt,j> as function of Df and Dh 0.1 < pT < 1.5 GeV/c <pi,pj> (MeV2) CERES 158 AGeV/c Pb-Au Preliminary • 7M events analyzed, 8% centrality

  17. Using mixing events • 7M events analyzed, 8% centrality • 2M mixed events analyzed <Dpt,iDpt,j> = 22.71+/- 0.32 MeV2 <Dpt,iDpt,j> = -0.20+/- 0.42 MeV2

  18. Normalized dynamical fluctuation SpT (%) CERES 158 AGeV/c Pb-Au Preliminary SpT = 100 * (<pt,i pt,j>)1/2 / pT<incl>(%) • On average : SpT ~ 1.04 % (agrees well with previous studies)

  19. <Dpt,iDpt,j> as function of Df and Dh CERES 158 AGeV/c Pb-Au Preliminary <Dpt,iDpt,j> = 22.71+/- 0.32 MeV2 s 2pT,dyn= 22.28 +/- 0.48 MeV2 0 < Dh < 0.1 • average value consistent • rich structure in Dh-Df • origin? 0.1 < Dh < 0.2 0.2 < Dh < 0.3 0.3 < Dh < 0.4 0.4 < Dh < 0.5 Overall fit 0 - 180 0 - 180 0 - 180 0 - 180 0 - 180 Df (degrees)

  20. <pi,pj> for different charge combinations (+) (+) (-) (-) (+) (-) • there are differences… • at Df < 7.5 deg. and small Dh (+) (+) and (-) (-) similar strength and shape •  origin could be the same (HBT, Coulomb?) • (+) (-) peak weaker and narrower •  Coulomb, resonances, e+e-? • away-side component (flow, minijets?) • What is the proton contribution ? CERES 158 AGeV/c Pb-Au Preliminary

  21. Centrality dependence CERES Pb-Au Preliminary <pi,pj> (MeV2) Npart • similar centrality dependence at SPS and RHIC

  22. Centrality dependence 0-5 % 10-20 % centrality 20-30 % CERES 158 AGeV/c Pb-Au Preliminary 40-50 % • peak structure enhances with centrality • could be elliptic flow, but only?

  23. Centrality dependence CERES 158 AGeV/c Pb-Au Preliminary <pi,pj> (MeV2) Dh= 0 - 0.5 Df

  24. <N><pt,i pt,j> vs Centrality non-monotonic centrality dependence is related to back-to-back structure (?)

  25. Two-particle correlations (cumulant pT variable c) No structure characteristic of event-by-event temperature fluctuations is observed NA49 nucl-ex/0208020

  26. Two-particle correlations (Df dependence) Dh= 0 - 0.5 all pairs CERES 158 AGeV/c Pb-Au Preliminary

  27. Two-particle correlations (Df dependence) Dh= 0 - 0.5 all pairs

  28. Two-particle correlations (Df dependence) Dh= 0 - 0.5 +/+

  29. Two-particle correlations (Df dependence) - / - Dh= 0 - 0.5

  30. Two-particle correlations (Df dependence) + / - Dh= 0 - 0.5

  31. <Dpt,iDpt,j> as function of Df and Dh

  32. Summary and conclusions <pt,i pt,j> as a function of Df and Dh(?) have been presented strong dependence on Df, Dh and + +, - -, + - has been observed integrated SpT is mainly given by small angle correlations there are hints of an away-side structure correction should be applied for detector effects (using mixing events) conclusive results require full statistics + comparison to models

  33. CERES Collaboration D. Adamova, G. Agakichiev, D. Antonczyk, A. Andronic, H. Appelshäuser, V. Belaga, J. Bielcikova, P. Braun-Munzinger, O. Busch, A. Castillo, A. Cherlin, S. Damjanovic, T. Dietel, L. Dietrich, A. Drees, S. Esumi, K. Filimonov, K. Fomenko, Z. Fraenkel, C. Garabatos, P. Glässel, G. Hering, J. Holeczek, V. Kushpil, B. Lenkeit, W. Ludolphs, A. Maas, A. Marin, J. Milosevic, A. Milov, D. Miskowiec, R. Ortega, Yu. Panebrattsev, O. Petchenova, V. Petracek, A. Pfeiffer, S. Radomski, J. Rak, Ravinovich, P. Rehak, W. Schmitz, J. Schukraft, H. Sako, S. Shimansky, S. Sedykh, J. Stachel, M. Sumbera, H. Tilsner, I. Tserruya, G. Tsiledakis, T. Wienold, B. Windelband, J.P. Wessels, J.P. Wurm, W. Xie, S. Yurevich, V. Yurevitch NPI ASCR, Rez, Czech Republic GSI Darmstadt, Germany Frankfurt University, Germany Heidelberg University, Germany JINR Dubna, Russia Weizmann Institute, Rehovot, Israel SUNY at Stony Brook, USA CERN, Switzerland BNL, Upton, USA Münster University, Germany MPI Heidelberg, Germany

  34. Short-range correlations (SRC) C2(qinv) all acceptance 0 < Df < 7.5 deg. , 0 < Dh < 0.1 p-,p- HBT + Coulomb 1 qinv (GeV/c) p-,p+ qinv (GeV/c) Coulomb + resonances • The peak at the origin is probably contaminated • by HBT+Coulomb 1 qinv (GeV/c) D.Antonczyk p - correlations for CERES

  35. Dependence on pT cuts 0.1 < pT < 0.8 GeV/c 0.1 < pT < 1.5 GeV/c CERES 158 AGeV/c Pb-Au Preliminary SpT ~ 1.02 % SpT ~ 1.14 % 0.6 < pT < 2 GeV/c 0.1 < pT < 2 GeV/c SpT ~ 1.24 % SpT ~ 0.46 %

  36. Centrality dependence 0-5 % centrality 5-10 % centrality CERES 158 AGeV/c Pb-Au Preliminary • <Dpt,iDpt,j> = 32.23 +/- 1.82 MeV2 • <Dpt,iDpt,j> = 24.05 +/- 1.28 MeV2 10-20 % centrality 20-30 % centrality • <Dpt,iDpt,j> = 41.39 +/- 7.12 MeV2 • <Dpt,iDpt,j> = 87.34 +/- 10.93 MeV2 • peak structure enhances • with centrality • could be elliptic flow, but only? 40-50 % centrality 30-40 % centrality • <Dpt,iDpt,j> = 134.54 +/- 20.12 MeV2 • <Dpt,iDpt,j> = 294.76 +/- 40.24 MeV2

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