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Femtoscopy with STAR

Femtoscopy with STAR. Zbigniew Chaj Ä™ cki for the Collaboration. Outline. Probing space and time in Heavy Ion Collisions with Femtoscopy Evolution and emission time Size and shape of the source Do we understand the transverse mass dependence of HBT radii?

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Femtoscopy with STAR

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  1. Femtoscopy with STAR Zbigniew Chajęcki for the Collaboration Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  2. Outline • Probing space and time in Heavy Ion Collisions with Femtoscopy • Evolution and emission time • Size and shape of the source • Do we understand the transverse mass dependence of HBT radii? • Underlying physics in AA: dynamically-driven geometric substructure • AuAu relative to pp (and dAu) • Problem with baseline of correlation function for p+p and d+Au collisions • Decomposition of correlation function in terms of spherical harmonics –new approach of studying particle correlations • Summary Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  3. The sketch of Heavy Ion Collision Femtoscopy probes the space and time in HIC dN/dt time hadronic phase and freeze-out QGP and hydrodynamic expansion hadronization initial state pre-equilibrium Emission time “temperature” Evolution time Chemical freeze out Thermal freeze out Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  4. Hydro predictions: Evolution and Emission time Hydrodynamic predictions Heinz & Kolb, hep-ph/0204061 • Long lifetime of the source • as signal of the QGP formation • Ro- Rs→Emission time • Rl→Evolution time • Hydrodynamic calculations reproduce momentum observables but fail to reproduce HBT results → RHIC HBT puzzle Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  5. Origin of HBT puzzle Evolution time Emission time Au+Au@200GeV Evolution time changes from ~9 fm/c for central collisions to ~5 fm/c for peripheral colisions 1.2 Blast Wave fit to spectra, v2 and HBT Hydro prediction:~ 15 fm/c Heinz & Kolb, hep-ph/0204061 Nparticipants 1.0 Nparticipants STAR - AuAu@200GeV, PRC71 (2005) 044906 Modified Sinyukov fit to RL M. Herrmann and G.F. Bertsch, PRC51 (1995) 328 * in the absence of transverse flow Short emission time (~2fm/c) consistent with RO/RS ratio Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  6. Properties of the source at freeze-out STAR, PRL93 012301 (2004) STAR, PRL93 012301 (2004) system changes the shape system expands eccentricity • estimate initial from Glauber • εfinalfrom asHBT: • Size of homogeneity region scales with initial source size (increase with increase of centrality of the collision -b→0 ) • Oscillation phases: out-of-plane extended source PRC66 (2002) 044903 Source remains out-of-plane at freeze out Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  7. Why do the HBT radii fall with increasing pT ? Au+Au@200GeV 0. 0. 0. .2 0.2 0.3 0.4 0.5 0.2 0.3 0.4 0.5 0.6 • Decrease of HBT radii with pT • usually attributed to collective flow • RL → longitudinal flow • RT→ transverse flow • Non-flow possibilities • termally (not collectively) expanding source • hot core surrounded by cool shell • important ingredient of Buda-Lund hydro picture (Csorgo et al.) t Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  8. STAR, Au+Au@200GeV STAR preliminary 2 Ratio of (AuAu, CuCu, dAu) HBT radii by pp p+p+X STAR preliminary Rlong • All pT(mT) dependences of HBT radii observed by STAR scale with pp although it’s expected that different origins drive these dependence • Is it only a coincidence or something deeper? Rout 1 Rside 0.25 0.5 pT HBT radii from p+p collisions fall with pT – as observed in the past, and usually attributed to string fragmentation Similar pT (mT) dependence as in p+p observed in d+Au collisions – do they have the same origin? 0.2 0.3 0.4 0.5 0.2 0.3 0.4 0.5 0.6 In Au+Au pT (mT) dependence attributed to collective expansion of the source mT mT HBT in Au+Au vs p+p (d+Au) Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  9. p+p like a little Au+Au? • flow not expected in such a small system as pp • Shuryak: a hydro approach cannot describe data in pp at RHIC – hep-ph/0405066 • Csorgo: mT dependence of HBT radii in pp is not generated by the transverse flow, but by the transverse temperature inhomegeneities of hadron-hadron collisions due to the freezing scale - hep-ph/0406042 Au+Au like superposition of p+p? • AuAu = N*(strings in pp) ? • AuAu = N*(„blast-waves”) ? NO! – that would generate local space-momentum correlations but in AuAu we see global correlations – although both scenarios would lead to the identical p-space observables Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  10. Initial vs Final Size : pp(dAu) vs AuAu STAR preliminary • AuAu mostly “understood” in terms of collective flow • pp (dAu) show apparent globalspace momentum correlations, but no (or little) expansion Model-dependent approach of veryfication of expansion scenario • RMS of initial size of the source calculated with Glauber model vs. experimental RSIDE for <kT>=0.2 GeV/c Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  11. Intriguing results ....Let’s take a closer look Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  12. Projection of 3D CF in d+Au STAR preliminary • Gaussian source vs non-Gaussianess of CF • It looks like fit describes the shape of correlation function d+Au central, kt: [0.25-0.35] GeV/c Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  13. Worst-case picture of d+Au STAR preliminary • Not great fit • One imagines one could do a better job, but fit must work in 3D; we see tiny portion of space • What is going on in the normalization region?(independent of Gaussian ansatz) • Problem with projections • cannot see systematics in 3D • experiments w/same CF will have different projections d+Au peripheral, kt: [0.15-0.60] GeV/c Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  14. Decomposition of CF onto spherical harmonics QLONG Q  QOUT  QSIDE Z.Ch., Gutierrez, Lisa, Lopez-Noriega, nucl-ex/0505009 • Cartesian-space (out-side-long) naturally encodes physics, but is poor/inefficient representation • Recognize symmetries of Q-space -- decompose by spherical harmonics! • Direct connection to source shapes [Danielewicz,Pratt: nucl-th/0501003] – decomposition of CF on cartesian harmonics • ~immune to acceptance • full information content at a glance[thanks to symmetries]  : [0,2p]  : [0,p] Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  15. Some properties of Alm coefficients • Alm = 0 for l or m odd – identical particle correlations (for non-id particles, odd l encodes shift information) • A00(Q) ≈ one-dimensional “CF(Qinv)” (bump ~ 1/R) • Alm(Q) = l,0 where correlations vanish • Al≠0,m(Q) ≠ 0  anisotropy in Q space • Im[Alm] = 0 Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  16. Simulations with Gaussian model RL < RT ~acceptance free RL > RT RO < RS Simple, Gaussian source calculations RO > RS Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  17. Decomposition of CF for centrald+Au collision Decomposition of CF for peripherald+Au collision Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  18. Baseline in p+p, d+Au and Au+Au • Some coefficients don’t vanish for large Q • Bias from zero is larger for more peripheral collisions • This problem is getting more significant for small systems (pp & dAu) • It can be due to • an experimental artifact • long range correlations (e.g. Jets) • problem with momentum conservation ? • or ? Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

  19. Summary • Femtoscopy indicates system evolution due to dynamic bulk behaviour • mT dependence of HBT radii for AuAu, dAu and pp seems to be the same although it’s expected (?) to have different origins • a new puzzle? • Looking in more details • baseline problem • Spherical harmonics allow efficent diagnostic of the correlation function • Use symmetry of the q-space • All information at a glance • Pratt and Danielewicz [nucl-th/0501003]: connection of one-to-one CF and spatial anisotropies • Investigation into the source of non-femtoscopic correlations under way Z. Chajęcki - Workshop on Femtoscopy at RHIC - BNL - June 21, 2005

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