Femtoscopy in heavy ion collisions Wherefore Whence Whither

Femtoscopy in heavy ion collisions: Wherefore, Whence, & Whither? Mike Lisa Ohio State University • Wherefore (=“why? ”) • motivation & (basic) formalism • Whence (=“from where? ”) • systematics over 2 decades • Whither (=“to where? ”) • or “wither”. . . ? http: //www-rnc. lbl. gov/TBS MAL, Pratt, Soltz, Wiedemann Ann Rev Nucl Part Sci 55 (2005) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 1

Spacetime - The characteristic of H. I. C. STAR, PRC 66 (2002) 034904 STAR, PRL 93 (2004) 252301 Ann. Rev. Nucl. Part. Sci. 46 (1996) 71 • Non-trivial space-time - the hallmark of R. H. I. C. • Initial state: dominates further dynamics • Intermediate state: impt element in exciting signals • Final state: • Geometric structural scale is THE defining feature of QGP • Temporal scale sensitive to deconfinement transition (? ) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 2

Extraction of length scales maximum-likelihood fit to usually used (even for non-id) Gaussian parameterization of a-b separation pa xa pb pa xa for identical pions p b • F(Qinv) = integratedxsquared Coulomb wavefunction b xb • “contamination” included via • NB: Gaussian source: not Gaussian CF mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 3

Reminder • Two-particle interferometry: p-space separation space-time separation ng R lo x 1 p 1 qside p 2 Rside x 2 qout qlong Rout source sp(x) = homogeneity region [Sinyukov(95)] connections with “whole source” always model-dependent Rside Pratt-Bertsch (“out-side-long”) decomposition designed to help disentangle space & time Rout mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 4

Disintegration timescale - INITIAL expectation 3 D 1 -fluid Hydrodynamics Rischke & Gyulassy, NPA 608, 479 (1996) with transition “ ” Long-standing favorite signature of QGP: • increase in , ROUT/RSIDE due to deconfinement transition • hoped-for “turn on” as QGP threshold is reached mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 5

Two decades of systematics A. D. Chacon et al, Phys. Rev. C 43 2670 (1991) G. Alexander, Rep. Prog. Phys. 66 481 (2003) 15 10 Heinz/Jacak Wiedemann/Heinz Csorgo Tomasik/Wiedemann Boal/Jennings/Gelbke 20 Lisa, Pratt, Soltz, Wiedemann AGS/SPS/RHIC HBT papers (expt) R = 1. 2 (fm) • A 1/3 “R = 5 fm” 5 ‘ 85 ‘ 90 ‘ 95 ‘ 00 ‘ 05 • Pion HBT @ Bevalac: “largely confirming nuclear dimensions” • Since 90’s: increasingly detailed understanding and study w/ high stats mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 6

Two decades of systematics 15 10 Heinz/Jacak Wiedemann/Heinz Csorgo Tomasik/Wiedemann Boal/Jennings/Gelbke 20 Lisa, Pratt, Soltz, Wiedemann AGS/SPS/RHIC HBT papers (expt) y |b| 5 p. T ‘ 85 ‘ 90 ‘ 95 ‘ 00 ‘ 05 • Pion HBT @ Bevalac: “largely confirming nuclear dimensions” • Since 90’s: increasingly detailed understanding and study w/ high stats mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 7

Repeating most basic sanity check at relativistic energies. . . Forget homogeneity regions or fancy stuff. Do femtoscopic length scales increase when they “should? ” p-p correlations * big bump small source Also • SPS [NA 44(‘ 99), NA 49(‘ 00)] • RHIC [STAR(‘ 05)] mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 8

Varying initial “source size” Au+Au s. NN =200 Ge. V Fixed b : vary A (& B!) • Generalize A 1/3 Npart 1/3 • not bad @ RHIC! • connection w/ init. size? Fixed A+B : vary b Likely scaling variable: Npart PHENIX, PRL 2004 b mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 9

• Generalize A 1/3 Npart 1/3 • not bad @ RHIC! • connection w/ init. size? NB: not constant density PHOBOS • Heavy and light data from AGS, SPS, RHIC • ~ s-ordering in “geometrical” Rlong, Rside • Mult ~ K( s)*Npart • source of residual s dep? • . . . Yes! common scaling • final state drives radii, not init. geometry • (breaks down s < 5 Ge. V) LPSW nucl-ex/0505014 mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 10

Entropy determines “everything” at bulk level (soft sector) ? c. f. Helen’s talk H. Caines (STAR) QM 05 We are not alone. . . NA 57 (open) STAR (filled) Tounsi, Mischke, Redlich NA 57 (open) STAR (filled) NPA 715 565 (2003) S. Manly (PHOBOS) QM 05 NB: scaling violated s < 4 Ge. V (as with femtoscopy) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 11

Refinement: chemical effects • different behaviour below/above AGS • violates “universal” scaling • baryon meson dominance Vf • neglect time/dynamics: gross F. O. geometry appears determined by N • chemistry • “universal” mean free path ~ 1 fm (!? ) ~ FO volume CERES, PRL 90 (2003) 022301 x-section: m. f. p mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 12

Messages from systematics • AB, |b|, Npart systematics • sanity check on overall size dependence • final state multiplicity/chemistry determines rough geometry. . . and that geometry is ~2 x initial size collective/flow-like expansion? probe anisotropically! c. f. Chajecki - lighter systems mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 13

Strongly-interacting 6 Li released from an asymmetric trap O’Hara, et al, Science 298 2179 (2002) What can we learn? ? in-planeextended transverse FO shape + collective velocity evolution time estimate check independent of RL(p. T) out-of-plane-extended Teaney, Lauret, Shuryak- nucl-th/0110037 mike lisa - Femtoscopy in relativistic heavy ion & collisions Hot Quarks 17 May 2006, Sardinia, Italy 14

small RS • observe the source from all angles with respect to RP • expect oscillations in HBT radii big RS mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 15

• observe the source from all angles with respect to RP • expect oscillations in HBT radii (including “new” cross-terms) e d si side out t ou R 2 out-side<0 when pair=135º mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 16

Measured final source* shape STAR, PRL 93 012301 (2004) R 2 out-side<0 when pair=135º ever see that symmetry at ycm ? * model-dependent, see Retiere & ion MAL PRC 70 044907 2004 mike lisa - Femtoscopy but in relativistic heavy collisions - Hot Quarks 17 May 2006, Sardinia, Italy 17

Measured final source* shape STAR, PRL 93 012301 (2004) central collisions mid-central collisions peripheral collisions Expected evolution: * model-dependent, see Retiere & ion MAL PRC 70 044907 2004 mike lisa - Femtoscopy but in relativistic heavy collisions - Hot Quarks 17 May 2006, Sardinia, Italy 18

Evolution of size and shape - “the rule of two” i nit ial = f ina l STAR PRL 93 012301 (2004) c. f. Chajecki - lighter systems ~ x 2 size increase ~ 1/2 shape reduction Initial size/shape estimated by Glauber calculation Final config according to Retiere & MAL PRC 70 044907 2004 mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 19

• non-trivial excitation function • does it make sense? Is it related to bulk dynamics? ü YES “Anisotropic sanity check” AGS: FO init RHIC: FO < init (approximately same centrality) s. NN (Ge. V) is relation b/t final and near quantitatively sensible? (in a toy model yes - for discusison if asked) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 20

Messages from systematics • AB, |b|, Npart systematics • sanity check on overall size dependence • final state multiplicity/chemistry determines rough geometry. . . • , |b|, s systematics • sanity check on shape evolution • geometric evolution ~ consistent with collective bulk dynamics (flow) look for dynamic signatures & substructure • more than T versus mass • more than spectral shapes • more than v 2 • . . . flow is defined by space-momentum correlations only femtoscopy can probe substructure of dynamic bulk behaviour mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 21

Geometric substructure? random (non-)system: all observers measure the “whole source” mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 22

Flow-generated substructure random (non-)system: all observers measure the “whole source” Specific predictions of bulk global collective flow: • space-momentum (x-p) correlations • faster (high p. T) particles come from • smaller source • closer to “the edge” mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 23

Strong flow confirmed by all expts. . . what agreement!! (what agreement? ) LPSW(05) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 24

Flow-dominated “Blast-wave” model PRC 70 044907 (2004) Spectra v 2 HBT mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 25

Decreasing R(p. T) • usually attributed to collective flow • flow integral to our understanding of R. H. I. C. ; taken for granted • femtoscopy the only way to confirm x-p correlations – impt check Non-flow possibilities • cooling, thermally (not collectively) expanding source • combo of x-t and t-p correlations early times: small, hot source late times: large, cool source mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 26

MAL et al, PRC 49 2788 (1994) Decreasing R(p. T) • usually attributed to collective flow • flow integral to our understanding of R. H. I. C. ; taken for granted • femtoscopy the only way to confirm x-p correlations – impt check Non-flow possibilities • cooling, thermally (not collectively) expanding source • combo of x-t and t-p correlations mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 27

Decreasing R(p. T) • usually attributed to collective flow • flow integral to our understanding of R. H. I. C. ; taken for granted • femtoscopy the only way to confirm x-p correlations – impt check Non-flow possibilities • cooling, thermally (not collectively) expanding source • combo of x-t and t-p correlations • hot core surrounded by cool shell • important ingredient of Buda-Lund hydro picture e. g. Csörgő & Lörstad PRC 54 1390 (1996) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 28

Each scenario generates x-p correlations but… Decreasing R(p. T) • usually attributed to collective flow • flow integral to our understanding of R. H. I. C. ; taken for granted • femtoscopy the only way to confirm x-p correlations – impt check x 2 -p correlation: yes x -p correlation: yes Non-flow possibilities • cooling, thermally (not collectively) expanding source • combo of x-t and t-p correlations • hot core surrounded by cool shell • important ingredient of Buda-Lund hydro picture e. g. Csörgő & Lörstad PRC 54 1390 (1996) t x 2 -p correlation: yes x -p correlation: no mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 29

Flow-dominated “Blast-wave” model PRC 70 044907 (2004) R (fm) Spectra v 2 HBT STAR PRL 91 262301 (2003) K m. T (Ge. V/c) space-momentum substructure mapped in detail mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 30

RHIC femtoscopy with wide variety of particle species R(√SNN, b, Npart, A, B, m. T, y, , PID 1, PID 2) p p + - K+ K- + - - K+ K- - - K 0 S p p K 0 S = prelim or final result available mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 31

Trends, soft sector, and RHI history Finally, we • unlike hard and understand it! “intermediate” sectors, soft sector has “decades” of systematics A. Wetzler (2005) Just one event! Then: p-dependent potentials, surface effects, hard-cores, absoption. . . M Gyulassy ‘ 95 mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 32

model comparisons • unlike hard and “intermediate” sectors, soft sector has “decades” of systematics • single-point agreement a bit unsatisfying. . . • femtoscopic model comparisons: mostly “HBT radii” in b=0 collisions • RHIC models only expected to work at highest energies. . . mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 33

Comparison to “perfect” hydro calculations LPSW(05) • model sensitivity (not just R=5) • Rout too big (too long emission time? ) • Rlong too big (too long evolution time? ) • Rside too small (? ) - Hot Quarks 17 May 2006, Sardinia, Italy mike lisa - Femtoscopy in relativistic heavy ion collisions 34

Comparison to Boltzmann/cascade models better! (better than “perfect”. . . ? ) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 35

What’s the difference? freeeze-out. . . . Eo. S. . . viscosity hydro “HBT radii” from variances cascade fit calculated* 3 D C(q) to Gaussian functional form: *later: how it is calculated theionsame IF- source mike lisa - Femtoscopy inshould relativisticbe heavy collisions Hot Quarksis 17 Gaussian May 2006, Sardinia, Italy 36

Non-Gaussian Effects and Model Comparisons Hydro/BW Frodermann, Heinz, MAL PRC 63 (2006) C 2 Hydrodynamics - CE EOS Hydrodynamics - NCE EOS Frodermann, Heinz, MAL PRC 63 (2006) Blast Wave C 2 Depending on model (& parameters, like Eo. S), non-Gauss effects mayqbe important, (also, Hirano, Ko/Li, Rischke) qs (Ge. V/c) • BW - no big effect • “perfect” hydro - pushes results into “right” direction. NCE Eo. S close RO KT (Ge. V/c) KRTS(Ge. V/c) KT (Ge. V/c) RL KT (Ge. V/c) qs (Ge. V/c) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 37

Wherefore & Whence R(√SNN, b, Npart, A, B, m. T, y, , PID 1, PID 2) • size & shape; timescale estimate • space-momentum substructure of a flowing system; dynamics and evolution of • radial flow (size and shift) • elliptic flow (shape and timescale) • directed flow (shape and tilt) [did not show due to time] • hadronic particle potentials / phase shifts • Femtoscopy: • • well-calibrated, well-established tool the one most directly connected to space-time - THE defining feature of R. H. I. C. huge set of systematics of consistent measurements sensitive to physics in models • with care: the femtoscope is a precision tool to apply to new systems LHC, p+p, etc mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 38

Whither? • non-id correlations for b≠ 0 [Retiere & Lisa PRCPRC 70 044907 (2004)] • invert the problem : low-energy phaseshifts from exotic pairs (e. g. - ) [talk of H. Gos] & [P. Chaloupta QM 05] • space-time substructure in p+p ? ? - “direct comparison] [talk of Z. Chajecki] [Chajecki et al, WW 05] • imaging - beyond sizes and shifts [Brown, Danielewicz, Pratt, & others] • first-order azimuthally-sensitive femtoscopy - spacetime aspects of v 1 [Lisa et al, PLB 489 287; PLB 496 1] • relative jets, spin. . (? ) • continue/expand rich program @ ALICE/LHC mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 39

THE END mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 40

Strong flow confirmed by all expts. . . Central (~10%) Au. Au (Pb. Pb) collisions at y~0 mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 41

A simple estimate – 0 from init and final • BW → X, Y @ F. O. ( X > Y) • hydro: flow velocity grows ~ t w l flo ” dia a r “ • From RL(m. T): 0 ~ 9 fm/c üconsistent picture • Longer or shorter evolution times X inconsistent P. Kolb, nucl-th/0306081 ütoy estimate: 0 ~ 0(BW)~ 9 fm/c • too short to account for expansion? ? • Need a real model comparison → as. HBT workable “evolutionary clock” constraint for models mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy MAL ISMD 03 42

Motivation Formalism Experiment Trends 1 D projections: a limited view Models STAR PRC 71 044906 (2005) • Usually, quality of data and fit shown in 1 D projections • Narrow integration best out “Gaussian fit” (remember: not Gaussian CF) • limited view of data • see talks of Adam, Scott, Sandra • tomorrow: a better way side long mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 43

Motivation Formalism Experiment Trends Models The perennial non-Gaussianness • Source has never been fully Gaussian. c. f. J. Sullivan @ SPS • periodically re-discovered, with little change; information condensation needed to observe systematic data trends • non-Gaussianness @ RHIC reported in first and subsequent HBT measurements • imaging is probably best solution (but even then. . . ) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 44

Motivation Formalism Experiment Trends Models The perennial non-Gaussianness CF is “mostly” Gaussian STAR tried “Edgeworth” functional expansion (Csorgo 2000) STAR PRC 71 044906 (2005) Rl (fm) RO/RS • 20% effect in Rlong! systematic error. . . ? • appears fit captures dominant scale- Hot Quarks 17 May 2006, Sardinia, Italy mike lisa - Femtoscopy in relativistic heavylength ion collisions RS (fm) RO (fm) among few quantitative estimates of non-Gaussian shape 45

Another implication of strong flow: ~ m. T scaling mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 46

• transverse shape: • non-trivial excitation function • increased flow*time rounder FO geometry @ RHIC • insufficient [flow]x[time] to become in-plane AGS: FO init RHIC: FO < init (approximately same centrality) using four of the six “radii” s. NN (Ge. V) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 47

using ALL of the six “radii” Au+Au s. NN = 2. 3 Ge. V; b 5 fm E 895, PLB 496 1 (2000) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 48

(o ) AGS • transverse shape: • non-trivial excitation function • increased flow*time rounder FO geometry @ RHIC • insufficient [flow]x[time] to become in-plane • Spatial orientation: • another handle on flow & time • HUGE tilts @ AGS!! • RHIC? • QGP-induced orientation? STAR: soon ? ? s. NN (Ge. V) y x qs z (Beam) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 49

v 1 predictions (QGP invoked) x-p transverse-longitudinal coupling may be affected in early (v 1) stage J. Brachmann et al. , Phys. Rev. C. 61 024909 (2000) L. P. Csernai, D. Rohrich: Phys. Lett. B 458 (1999) 454 mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 50

(o ) AGS • transverse shape: • non-trivial excitation function • increased flow*time rounder FO geometry @ RHIC • insufficient [flow]x[time] to become in-plane • Spatial orientation: • another handle on flow & time • HUGE tilts @ AGS!! • RHIC? • QGP-induced orientation? • requires true 3 D dynamical model (explicitly non-B. I. ) STAR: soon ? ? ? s. NN (Ge. V) y x qs z (Beam) mike lisa - Femtoscopy in relativistic heavy ion collisions - Hot Quarks 17 May 2006, Sardinia, Italy 51