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Two Particle Interferometry at RHIC

Two Particle Interferometry at RHIC. Sergey Panitkin (Brookhaven National Laboratory). Outline. Introduction and Motivation Summary of Results from AuAu 130 GeV Results from AuAu 200 GeV PHOBOS PHENIX STAR (see talks by M. Lisa, V. Okorokov) Summary and outlook. q Side. q Out. p y.

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Two Particle Interferometry at RHIC

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  1. Two Particle Interferometry at RHIC Sergey Panitkin (Brookhaven National Laboratory) Sergey Panitkin

  2. Outline • Introduction and Motivation • Summary of Results from AuAu 130 GeV • Results from AuAu 200 GeV • PHOBOS • PHENIX • STAR (see talks by M. Lisa, V. Okorokov) • Summary and outlook Sergey Panitkin

  3. qSide qOut py px Pratt-Bertsch Parameterization Decomposition of the pair relative momentum (measured in the LCMS frame; (p1+ p2)z=0) • Information: • geometrical source size: Rside • lifetime • (for simple sources!) • Rside2=R0ut2-(bpairt)2 Sergey Panitkin

  4. Pion Correlation Functions at RHIC STAR 130 GeV Open symbols – No Coulomb Solid – Coulomb corrected Red line – Gaussian fit Experimental effects that were evaluated: Single track cuts Track merging Track splitting PID Impurities Finite radius Coulomb Momentum resolution Event vertex mixing Sergey Panitkin

  5. In Search of the QGP. Naïve expectations QGP has more degrees of freedom than pion gas Entropy should be conserved during fireball evolution Hence: Look in hadronic phase for signs of: Large size, Large lifetime, Expansion…… Sergey Panitkin

  6. In search of the QGP: Expectations • “Naïve” picture (no space-momentum correlations): • Rout2=Rside2+(bpairt)2 • One step further: • Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ 2->4 @ kt = 350 MeV. • Looking for a “soft spot” Rside Rout Sergey Panitkin

  7. Excitation function of the HBT parameters • ~10% Central AuAu(PbPb) events • y ~ 0 • kT0.17 GeV/c • no significant rise in spatio-temporal size of the  emitting source at RHIC Note ~100 GeV gap between SPS and RHIC ! Sergey Panitkin

  8. The Rout/Rside Ratioat 130 GeV (S. Soff et al) Hydro +UrQMD STAR Smaller observed ratio than expected from theory. Different KT dependence. Data -> Short freeze-out Model -> Extended freeze-out ERHIC HBT Puzzle Sergey Panitkin

  9. RHIC HBT PUZZLE Small Rout implies small Dt P.Kolb Small Rbeam implies small lifetime t, ~10 fm/c Large Rside implies large R But Hydro fits spectra and v2 nicely! Sergey Panitkin

  10. STAR 130 GeV PHENIX 130 GeV p + p - RHIC HBT Puzzle Most “reasonable” models still do not reproduce RHIC √SNN = 130GeV HBT radii Hydro + RQMD PHENIX PRL 88 192302 (2002) √SNN = 130GeV • “Blast wave” parameterization (Sollfrank model) can approximately describe data at 130 GeV • …but emission duration must be small •  = 0.6 (radial flow) • T = 110 MeV • R = 13.5  1fm (hard-sphere) • emission= 1.5  1fm/c (Gaussian) from spectra, v2 Sergey Panitkin

  11. PHENIX kT dependence of source radii Centrality is in top 30% Sergey Panitkin

  12. PHENIX Centrality dependence @ 200 GeV 0.2<kT<2.0GeV/c, <kT>=0.46GeV/c Fit with p0+p1*Npart^1/3 Rlong increases more rapidly with the Npart than Rout. Rlong ~ Rside Sergey Panitkin

  13. 200GeV Central Midcentral Peripheral Centrality and mT dependence at 200 GeV STAR PRELIMINARY RL varies similar to RO, RS with centrality HBT radii decrease with mT (flow) Roughly parallel mT dependence for different centralities RO/RS ~ 1 (short emission time) Sergey Panitkin

  14. 200GeV - 130 GeV Central Midcentral Peripheral PHENIX Central * Comparison to 130 GeV. Transverse radii STAR PRELIMINARY • Higher B-field  higher pT • Transverse radii: • similar but not identical • low-pT RO, RS larger at 200 GeV • steeper falloff in mT • (PHENIX 130GeV) • Ro falls steeper with mT Statistical errors only Sergey Panitkin

  15. Rout/Rside Ratios at 200 GeV Ratio is <1 at high Pt (but note different centralities!) Errors are statistical + systematic Sergey Panitkin

  16. 200GeV - 130 GeV Central Midcentral Peripheral PHENIX Central * Evolution timescale from RL Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow) Makhlin and Sinyukov, Z. Phys. C 39 (1988) 69 Assuming TK=110 MeV(from spectra at 130 GeV) STAR PRELIMINARY (fit to STAR 200GeV data only) Longitudinal radius: at 200GeV identical to 130 GeV rapid evolution!!! Sergey Panitkin

  17. What have we learned about pion source S(x,p) ? • Pion spectra shapes plus HBT RO,S,L(KT): • T ~ 100 MeV • <r> ~ 0.6 • R ~ 12 fm • t0~10 fm/c • Rout/Rside described by sharp radial cut-off and brief emission duration,Dt~2 fm/c which squeezes Rout • Increased pion phase space density (see talk by R. Lednicky) • Azimuthal dependence points toward fast break up of the source (see talk by M. Lisa) Sergey Panitkin

  18. Comparison of kaons to pions In the most 30% central Mt scaling violation ? Sergey Panitkin

  19. Vo Mean ~ 3.79 / Event pT ~ 1 GeV/c mT ~ 1.12 GeV/c2 counts Number of events Number of K0s pT(GeV/c) STAR K0s Reconstruction DCA between daughters DCA of V0 to primary vertex DCA of daughters to primary vertex Decay Length DCA – distance of closest approach Sergey Panitkin

  20. blue: signal from fit red : noise S/N = 19.11 counts CF STAR PRELIMINARY STAR PRELIMINARY 0.46 0.48 0.50 0.52 Minv (GeV/c2) Qinv (GeV/c) K0sK0s Correlations from STAR • no coulomb interaction • less affected by long-lived resonance feed-down • extend systematic to higher pT • strangeness dynamics • unique measurement A promising low-Q correlation! l=0.76 0.29 Rinv=5.75 ± 1.0 fm Large source for <mT> ~ 1.12 GeV/c2 ??? systematic study underway… Sergey Panitkin

  21. Summary • Lots of new data from all RHIC experiments ! • So far no obvious inconsistencies in pion HBT data • pp interferometry: • sources sizes at 200 roughly same as at 130GeV, with similar systematics: • radii decrease with mT: consistent with radial flow • mT dependence independent of centrality • RO/RS ~ 1 over large Pt range: short emission duration t • RL(mT): Sinyukov fits → evolution time: <t> ≈ 10fm/c • systematics study underway • Kaon interferometry: • Mt scaling violation (Charged kaons –PHENIX, K0 – STAR) ? • More data needed (coming soon!) • More data to come soon ! Need theoretical explanation! Sergey Panitkin

  22. b s R Fireball dynamics: Collective expansion Shape of the mT spectrum depends on particle mass Inverse-slope depends on mT-range where and Description of freeze-out inspired by hydrodynamics Flow profile used r =s (r/R)0.5 The model is from E.Schenedermann et al. PRC48 (1993) 2462and based on Blast wave model Sergey Panitkin

  23. Blast wave at 200 GeV: Fails? From the spectra (systematic errors): T = 0.7 ± 0.2 syst. Tfo = 110  23 syst. MeV J. Burward-Hoy(QM2002) PHENIX Preliminary Rs (fm) Ro (fm) RL (fm) • 10% central negative pion HBT radii. • Systematic uncertainty in the data is 8.2% for Rs, 16.1% for Ro, 8.3% for RL. -- R = 9.7±0.2 fm 0 = 132 fm/c Model by Wiedemann, Scotto, Heinz, PRC 53 (No. 2), Feb. 1996 Sergey Panitkin

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