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Current Status of the RHIC HBT Puzzle

Current Status of the RHIC HBT Puzzle. Sergey Panitkin Brookhaven National Lab La Thuile, March 18, 2005. 99.5%. Who cares about the soft sector?. Well-justified excitement about high-p T physics. But recall that we want to create/study a new type of matter (= bulk system)

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Current Status of the RHIC HBT Puzzle

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  1. Current Status of the RHIC HBT Puzzle Sergey Panitkin Brookhaven National Lab La Thuile, March 18, 2005 Sergey Panitkin

  2. 99.5% Who cares about the soft sector? • Well-justified excitement about high-pT physics • But recall that we want to create/study a new type of matter (= bulk system) • large-scale (soft?) deconfinement • Collective properties (T,p, flow?) • Jets/ect are probes of this system • Crucial to understand bulk properties and dynamics in their own right Sergey Panitkin

  3. Collective behavior at RHIC P. Kolb, J. Sollfrank, U. Heinz • Hydrodynamics seems to reproduce p-space aspects (spectra and elliptical flow) of particle emission up to pT~2GeV/c • Bulk system?!Note: Hydro provides complete space-time evolution. Can be tested! Heinz & Kolb, hep-th/0204061 Sergey Panitkin

  4. Two-particle Correlations Single particle spectrum is sensitive to momentum distribution only Relative momentum distribution of particle pairs is sensitive to space-time information FSI Source function Intensity interferometry, HBT technique, etc…. Sergey Panitkin

  5. Two particle Interferometry: Idealized case For non-interacting identical bosons: emission function Sergey Panitkin

  6. Au+Au R ~ 6 fm p+p R ~ 1 fm d+Au R ~ 2 fm Correlation functions for different colliding systems STAR preliminary C2(Qinv) Qinv (GeV/c) Correlations have more information One can use more sophisticated analysis to extract it Sergey Panitkin

  7. “Standard” Pratt-Bertsch coordinate system Sergey Panitkin

  8. HBT for Gaussian sources Decompose q into components: qLong: in beam direction qOut : in direction of transverse momentum KT qSide:  qLong & qOut Radii are related to source variances: Sensitive to emission time Sensitive to transverse extent Sensitive to longitudinal extent In Longitudinally Co-Moving System (LCMS) bl =0 Sergey Panitkin

  9. 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

  10. In Search of the QGP. Expectations. “Energy density” • One step further: • Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ 2->4 @ Kt = 350 MeV. • Looking for a “soft spot” Sergey Panitkin

  11. 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 • Ro/Rs ~ 1 • Some rise in Rlong Note ~100 GeV gap between SPS and RHIC Sergey Panitkin

  12. RHIC Energy Scan • Measurements at 200, 130, 62 GeV • No significant change with energy • Ro/Rs ~1 Where are signs of phase transition?! Is HBT sensitive to geometry at all?! PHOBOS nucl-ex/0409001 Sergey Panitkin

  13. More Experimental Systematics b≠0 STAR PRL 93:12301 (2004) PHENIX nucl-ex/0401003 Centrality dependence asHBT Clear sensitivity to source geometry ! Sergey Panitkin

  14. Ry Rx Source expansion at RHIC STAR Collaboration, nucl-ex/0312009 initial = final STAR preliminary Expansion at low Pt Change in eccentricity of the source Sergey Panitkin

  15. the puzzle Model Comparison (the puzzle) • Subset of models shown • Broad range of physics scenarios explored • Good description of p-space • Poor description of HBT data Sergey Panitkin Does Rout/Rside of unity imply no long-lived mixed phase?

  16. x-t Correlation of Source Function positive! Why hydro doesn’t work? Positive? Negative? Rout~Rside may require positive x-t corr. t t Hubble like flow? Buda-Lund, AMPT Typical source function from hydro with Bjorken flow x x Negative x-t correlation Positive x-t correlation Sergey Panitkin

  17. BudaLund fits to 130 GeV data Parameterization, not a model ! PRC54 (1996) 1390, NPA 590 (1995) 465 Sergey Panitkin

  18. Conclusions • Rich set of experimental HBT results exists at RHIC • Large number of models has been developed to explain RHIC physics • Good description of momentum space observables • Evidence that matter at RHIC exhibits collective bulk properties • Most models still can not reproduce simultaneously experimental observables at low Pt: v2, spectra, correlations, dN/dy, etc • We are gaining better understanding of model failures • Bjorken longitudinal boost-invariance assumption seems to be one of the sources of discrepancies (at least for Hydrodynamical models) • More detailed correlation measurements will be available soon: non-identical correlations, HBT Pt>1 GeV/c, Kaons, protons, etc • Stay tuned! Sergey Panitkin

  19. The END Sergey Panitkin

  20. Back Up slides Sergey Panitkin

  21. Does HBT in rhic make sense? YES… • Size [R(Npart1/3)] • Shape [R( )] • Dynamic structure [R(mT)] … and NO • Model disagreement [transport] • Too-short timescales [BW] • Inconsistent dynamical picture • No large rise in RO, RL[general] Sergey Panitkin

  22. Buda-Lund fits to 130 GeV data Sergey Panitkin

  23. Freeze-out eccentricity can be estimated from relative amplitudes • Blast-wave: rel. amplitudes sensitive to spatial anisotropy, depend weakly on collective flowRetiere and Lisa, nucl-th/0312024 no temporal component Fourier coefficients of HBT() oscillations means relative amplitudes • 0th-order FC: centrality & kT dependence mirrors -integrated analyses; quantitatively consistent • Relative amplitudes increase from central to peripheral collisions STAR Collaboration, nucl-ex/0312009 Sergey Panitkin

  24. Comparison to PHENIX AuAu 200 GeV 30% Centrality Sergey Panitkin

  25. Elliptic geometry leads to oscillations of the radii For example Rside Out-of-plane Circular In-plane Rside2 (fm2) f (degree) HBT with respect to reaction plane fp=90° Rside (small) Rside (large) Reaction plane fp=0° out-of-plane extended source Naïve view with no flow Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002) Sergey Panitkin

  26. Rlong p1 x1 p2 qside Rside x2 qout qlong Rout • HBT: Quantum interference between identical particles 2 C (q) Gaussian model (3-d): 1 • Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for q (GeV/c) Hanbury Brown-Twiss interferometry • Two-particle interferometry: p-space separation  space-time separation Sergey Panitkin

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