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

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

Pratt-Bertsch Parameterization px qOut py qSide 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

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

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

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

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

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

But Hydro fits spectra and v2 nicely! 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

RHIC HBT Puzzle Most “reasonable” models still do not reproduce RHIC √SNN = 130GeV HBT radii Hydro + RQMD STAR 130 GeV PHENIX 130 GeV p + p - 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  1 fm/c (Gaussian) from spectra, v2 Sergey Panitkin

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

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

Centrality and mT dependence at 200 GeV Midcentral Peripheral 200GeV 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

Comparison to 130 GeV. Transverse radii STAR PRELIMINARY * Central Midcentral Peripheral PHENIX Central 200GeV - 130 GeV 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 Boris is a great guy! Statistical errors only Sergey Panitkin

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

Evolution timescale from RL Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow) * Central Midcentral Peripheral PHENIX Central 200GeV - 130 GeV 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

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

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

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

K0sK0s Correlations from STAR STAR PRELIMINARY S/N = 19.11 Minv (GeV/c2) counts 0.46 0.48 0.50 0.52 blue: signal from fit red : noise no coulomb interaction less affected by long-lived resonance feed-down extend systematic to higher pT strangeness dynamics unique measurement Qinv (GeV/c) CF STAR PRELIMINARY 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

Summary pp interferometry: 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

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 R b s Flow profile used r =s (r/R)0.5 The model is from E.Schenedermann et al. PRC48 (1993) 2462 and based on Blast wave model Sergey Panitkin

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) -- R = 9.7±0.2 fm 0 = 132 fm/c 10% central negative pion HBT radii. Systematic uncertainty in the data is 8.2% for Rs, 16.1% for Ro, 8.3% for RL. Model by Wiedemann, Scotto, Heinz, PRC 53 (No. 2), Feb. 1996 Sergey Panitkin