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status of RHIC femtoscopy program

status of RHIC femtoscopy program. Mike Lisa Ohio State University. Outline. Present directions increasing quality/interpretability fitting methods parallel focus of the program status of systematics and results. Overview of status at RHIC quality of measured correlations

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status of RHIC femtoscopy program

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  1. status of RHIC femtoscopy program Mike Lisa Ohio State University mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  2. Outline • Present directions • increasing quality/interpretability • fitting methods • parallel focus of the program • status of systematics and results • Overview of status at RHIC • quality of measured correlations • fitting methods • focus of study • systematics and results Open issues during discussions mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  3. Outline • Present directions • increasing quality/interpretability • fitting methods • parallel focus of the program • status of systematics and results • Overview of status at RHIC • quality of measured correlations • fitting methods • focus of study • systematics and results Open issues mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  4. hydro P. Chaloupka QM06 STAR PRC 71 (2005) 044906 STAR PRC 71 (2005) 044906 High-quality correlation functions (~99% level for ) excellent statistics, PID, acceptance great care taken in (e.g.) event-mixing mature techniques Distillation of information mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  5. pa pa pb pb xa xa xb xb Distilling the information • Usually, the ~104 datapoints in CF are distilled into ~8-12 numbers • (still true today...) • commonly used to fit CF: kernel-convoluted Gaussian function S • resulting “HBT radii” characterize size, shape, orientation in spacetime • frequent approximation for light particles: K-P eq. mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  6. mass s pT R(√SNN, b, Npart, A, B, mT, y, ,PID) • Vary colliding system • does physics change? • requires dedicated program • Vary kinematic variables • space-time dynamics • requires large acceptance • Vary particle type • consistent picture? • unique probe of dynamical structure • requires good particle identification & acceptance mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  7. DNP/JPS 2005, J. Newby PRL 93 012301 ‘04 asHBT: Source anisotropy mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  8. …   /2 R  2R asHBT: Source anisotropy mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  9. …   /2 R  2R asHBT: Source anisotropy ppt scale 1”=5 fm 20-30% 30-80% 0-5% mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  10. Spectra v2 HBT slow  emission fast  emission Geometric substructure: expansion is explosive • All signatures of explosive flow observed • momentum-space-only (spectra, v2) • falling pion “radii” with mT mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  11. R (fm)  emission region mT (GeV/c) K emission region Geometric substructure: expansion is explosive • All signatures of explosive flow observed • momentum-space-only (spectra, v2) • falling pion “radii” with mT • falling other “radii” with mT mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  12. PRL 91 262301 (2003)  emission region K emission region Geometric substructure: expansion is explosive • All signatures of explosive flow observed • momentum-space-only (spectra, v2) • falling pion “radii” with mT • falling other “radii” with mT • mass-ordered shift patern mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  13. PHOBOS PRC73, 031901(R) (2006) D. Flierl, PhD thesis 2002 Geometric substructure: expansion is explosive • All signatures of explosive flow observed • momentum-space-only (spectra, v2) • falling pion “radii” with mT • falling other “radii” with mT • mass-ordered shift patern • longitudinal scale and y-dependence consistent with boost-invariant scenario mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  14. Similar kinematic, mass behaviours at different s (up to a scale) PRC 71 044906 (2005) Similar kinematic behaviours at different |b| (up to a scale) Ann. Rev. Nucl. Part. Sci.55, 311 (2005) Factorization and universality R(√SNN, b, Npart, A, B, mT, y, ,m1,m2)  RG(√SNN, b, Npart, A, B)*D(mT, y, ,m1,m2) mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  15. Factorization and universality R(√SNN, b, Npart, A, B, mT, y, ,m1,m2)  RG(√SNN, b, Npart, A, B)*D(mT, y, ,m1,m2)  RG(dN/d)*D(mT, y, ,m1,m2) As “all” soft-physics observables @ RHIC, multiplicity driven at broad scale -> hydro-esque (entropy dominance) ? NB: factorization unclear for Rout, asHBT, long-range tails mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  16. hydro cascade Comments on model comparisons • mature comparisons exist (largely with pion HBT radii), enjoying some measure of success • unfortunately (generic curse): difficult to test against our hard-earned systematics since these models are “only valid at RHIC” • exception: HRM, often thought to be valid nowhere... • still, indications away from softest point, etc • interpretation clouded by apples::oranges comparisons... mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  17. Beyond the 99% level... more details, more questions • Data: Many efforts to improve experimental analysis • Fitting: Alternate fitting parameterizations mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  18. Ratio of (AuAu, CuCu, dAu) HBT radii by pp STAR preliminary mT (GeV) mT (GeV) pp, dAu, CuCu - STAR preliminary An overdose of universality • pT-dependence of length scales in p+p collisions “very” similar to that in A+A mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  19. STAR preliminary d+Au peripheral collisions Gaussian fit BUT... Clear interpretation clouded by data features Non-femtoscopic q-anisotropic behaviour at large |q| does this structure affect femtoscopic region as well? mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  20. STAR preliminary d+Au peripheral collisions QLONG Q  Gaussian fit QOUT  QSIDE Spherical harmonic decomposition as data diagnostic nucl-ex/0505009 • femtoscopic correlation at low |q| • must vanish at high |q|. [indep “direction”] mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  21. STAR preliminary d+Au peripheral collisions Gaussian fit Decomposition of CF onto Spherical Harmonics non-femtoscopic structure (not just “non-Gaussian”) Z.Ch., Gutierrez, MAL, Lopez-Noriega, nucl-ex/0505009 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  22. Not only for “very” small systems see talk of Z. Chajecki • believed largely due to global N-particle correlations. • much effort into diagnosis, disentangling • M. Kopytine: Similar issues for non-identical particle correlations in d+Au collisions • -- “shift” in emission points -> flow in d+A? is our data under sufficient control to extract fine details of femtoscopy? STAR preliminary mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  23. Complicating detailed fits, centrality dependence • Thought due to <pT> fluctuations. In progress • Again, neglecting non-femtoscopic correlations not justified (& if one doesn’t look, one might not know he has a problem) Issues in the fine details - non-id particle correlations Adam Kisiel mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  24. Correlated ‘contamination’ in (anti-)baryon correlations Typically one considers “contamination” in terms of uncorrelated pairs (mid-id, weak decays, ...) Fits are kernel-filtered Gaussian sources 30-80% measured CF is just “diluted” true CF (e.g. “”) 0-10% H. Gos; see talk by A. Kisiel mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  25. Correlated ‘contamination’ in (anti-)baryon correlations Crucial to extract reliable source estimates STAR, PRC74 (2006) 064906 H. Gos; see talk by A. Kisiel mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  26. Now, more detailed fitting (Assuming/hoping that DATA is quite under control) mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  27. “NCE” EoS  Ro Rs RL dN/dx PRC73 044908 (2006 KT (GeV/c) STAR Phys. RevC 71 (2005) 044906 Retiere & MAL PRC70 044907 (2004) Improving Gaussian ansatz • Sufficient statistics -> no CF fully Gaussian • No “realistic” model fully Gaussian • Comparisons to “HBT radii” typically improve when CF generated from Smodel • Look at two good/popular alternatives mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  28. 3) Sum of splines (imaging) 1) Gaussian source 2) Physical model source (Towards Scott’s dream) pa pa pb pb xa xa xb xb Distilling the information, redux • Usually, the ~103 datapoints in CF are distilled into ~5-10 numbers(still true today...) • source parameters varied to minimize 2 b/t measurement & kernel-filtered source mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  29. pi-Xi correlations - many technical improvements Gaussian fit • Improvements render “artifacts” < % • Now can fit, individually, four  correlations • ~consistent. • tendency for smaller shift of anti-baryon? (B-bars all produced) Petr Chaloupka; see talk of M. Sumbera mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  30. pi-Xi correlations - many technical improvements • Improvements render “artifacts” < % • Now can fit, individually, four  correlations • ~consistent. • tendency for smaller shift of anti-baryon? (B-bars all produced) • dynamic evidence of “early freezeout”??  (fm/c) Such fitting methods will be important to establish errorbars on EoS, etc, in larger context RSource (fm) Petr Chaloupka; see talk of M. Sumbera mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  31. lmax =0 Imaging - Spline source • 1D images show large-r behaviour, arising from small-q part of CF • significant tail beyond “Gaussian” PHENIX, Phys. Rev. Lett. 98, 132301 (2007) , mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  32. lmax =0 Imaging - Spline source • 1D images show large-r behaviour, arising from small-q part of CF • significant tail beyond “Gaussian” • STAR[prelim] versus PHENIX[final] • signif discrepancies in interesting region • errorbars understood? • DATA under control at required level? • method stability? STAR prelim see talk of Michal Bystersky mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  33. Brown, Soltz, Newby, Kisiel nucl-th/0705.1337 First model comparisons - 1D images • Statistical: BW-type emission function (Therminator) • most  emitted directly from decay •  (h/G=24 fm) important • tail underpredicted mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  34. First model comparisons - 1D images • Statistical: BW-type emission function (Therminator) • most  emitted directly from decay •  (h/G=24 fm) important • tail underpredicted • Dynamical: rescattering model (HRM) • naturally generates tail in separation distribution of “core” pions •  ? • good agreement at low pT • tail overpredicted at higher pT Central collisions, .20 < pT <.36 GeV Central collisions, .48 < pT <.60 GeV Also, Csanad, Csörgo, Nagy hep-ph/0702032 Core: ,,K* Halo: ,’,, PHENIX, R. Vertesi, WWND07 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  35. lmax > 0 Including higher-l terms (shapes) • holds hope to distinguish source of tail • resonances (core/halo)? • flow/rescattering • long-lived core component? • see many talks at this meeting... PHENIX, R. Lacey WPCF06 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  36. pa pa pb pb xa xa xb xb Parallel focus - vary kernel parameters, too mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  37. pa pa pb pb xa xa xb xb Parallel focus - vary kernel parameters, too STAR, PRC 2006 • First-ever p-, p-, p- correlations • Consistency from baryon sector for flow-generated x-p correlations • Extraction of real/imaginary p-, p- scattering lengths from CF !! • important new physics direction mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  38. F. Retiere WPCF05 see talk of M. Bysersky / M. Sumbera mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  39. Topics • Present directions • “relentless pursuit of excellence”: attacking new, non-trivial expt issues at 1/1000 level • fitting: • kernel-filtered splines (imaging) • model-cum-fit parameters (towards Scott’s dream) • increasing parallel focus on inverting the femtoscopic paradigm (phase shifts) • beginning program • systematics • identification of driving physics • model comparisons • Status at RHIC to-date • high-quality correlation functions “at 99% level;” excellent consistency between expts • (typically) source characterization with kernel-filtered Gaussians • focus on extracting femtoscopic information per se • extensive systematics • identification of “universalities” • detailed characterization of dynamic source • some mature model comparisons mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  40. Danke mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  41. Slides from Dave Brown’s (excellent) talk at WPCF05 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  42. Generalized Splines: • Nb=0 is histogram, • Nb=1 is linear interpolation, • Nb=3 is equivalent to cubic interpolation. • Recursion relations == fast to evaluate, differentiate, integrate • Resolution controlled by knot placement • Form basis for R2, but not orthonormal Representing the Source Function Radial dependence of each term in terms of Basis Splines: Dave Brown, WPCF05 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  43. this is an ill-posed problem • kernel not square • kernel possibly singular • noisy data • error propagation Practical solution to linear inverse problem, minimize : Most probable source is: With covariance matrix: The inversion process Koonin-Pratt eq. in matrix form: Dave Brown, WPCF05 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  44. Where Cartesian harmonics give analogous expressions Breaking Problem into 1d Problems Expand in Ylm’s and Legendre polynomials: Dave Brown, WPCF05 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

  45. What do the terms mean? • l = 0 : Angle averaged correlation, get access to Rinv • l = 1 : Access to Lednicky offset, i.e. who emitted first (unlike only) • l = 2 : Shape information: access to RO, RS, RL: C20 RL C00-(C20±C22)  RS ,RO • l = 3 : Boomerang/triaxial deformation (unlike only) • l = 4 : Squares off shape Dave Brown, WPCF05 mike lisa - femtoscopy status - WPCF August 2007, Santa Rosa, CA

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