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

2. Sergey Panitkin Who cares about the soft sector? 99.5% Well-justified excitement about high-p T 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

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

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

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

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

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

8. Sergey Panitkin HBT for Gaussian sources Decompose q into components: q Long : in beam direction q Out : in direction of transverse momentum K T q Side :  q Long & q Out Radii are related to source variances: In Longitudinally Co-Moving System (LCMS)  l =0 Sensitive to emission time Sensitive to transverse extent Sensitive to longitudinal extent

9. 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……

10. Sergey Panitkin 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”

11. Sergey Panitkin Excitation function of the HBT parameters ~10% Central AuAu(PbPb) events y ~ 0 k T 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

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

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

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

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

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

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

18. Sergey Panitkin 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!

19. Sergey Panitkin The END

20. Sergey Panitkin Back Up slides

21. Sergey Panitkin Does HBT in rhic make sense? YES… Size [R(N part 1/3 )] Shape [R( )] Dynamic structure [R(m T )] … and NO ?Model disagreement [transport] ?Too-short timescales [BW] ?Inconsistent dynamical picture ?No large rise in R O, R L [general]

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

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

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

25. Sergey Panitkin  Elliptic geometry leads to oscillations of the radii –For example R side R side 2 (fm 2 ) Out-of-planeIn-planeCircular  (degree) out-of-plane extended source  p =0°  p =90° R side (large) Reaction plane R side (small) Naïve view with no flow HBT with respect to reaction plane Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)

26. Sergey Panitkin q out q side q long Hanbury Brown-Twiss interferometry R side R long R out x1x1 x2x2 p1p1 p2p2  Two-particle interferometry: p-space separation  space-time separation  HBT: Quantum interference between identical particles q (GeV/c) C (q) 1 2 –Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for Gaussian model (3-d):