STAR HBT 4 oct 2002malisa - seminar IUCF1 Two-particle correlations and Heavy Ion Collision Dynamics...

4 oct 2002 malisa - seminar IUCF 1

STARHBT

Two-particle correlations and Heavy Ion Collision Dynamics at RHIC/STAR

Mike Lisa, Ohio State UniversitySTAR Collaboration

• Motivation / STAR

• Central collision dynamics – spectra & HBT(pT)

• Non-central collision dynamics – elliptic flow & HBT()• Further info from correlations of non-identical particles• Consistent picture of RHIC dynamics• Conclusions


STARHBT

Why heavy ion collisions?

• Study bulk properties of nuclear matter

The “little bang”

• Extreme conditions (high density/temperature) expect a transition to new phase of matter…

• Quark-Gluon Plasma (QGP)• partons are relevant degrees of freedom over

large length scales (deconfined state)

• believed to define universe until ~ s

• Heavy ion collisions ( “little bang”)• the only way to experimentally probe

deconfined state

• Study of QGP crucial to understanding QCD• low-q (nonperturbative) behaviour

• confinement (defining property of QCD)

• nature of phase transition


STARHBT

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

Relativistic Heavy Ion Collider (RHIC)

2:00 o’clock

4:00 o’clock6:00 o’clock

8:00 o’clock

10:00 o’clock

STARPHENIX

RHIC

AGS

LINACBOOSTER

TANDEMS

9 GeV/uQ = +79

1 MeV/uQ = +32

HEP/NP

g-2

U-lineBAF (NASA)

PHOBOS12:00 o’clock BRAHMS

• 2 concentric rings of 1740 superconducting magnets• 3.8 km circumference• counter-rotating beams of ions from p to Au• max center-of-mass energy: AuAu 200 GeV, pp 500 GeV

RHIC RunsRun I: Au+Au at s = 130 GeVRun II: Au+Au and pp at s = 200 GeV


STARHBT

The STAR Collaboration

451 Collaborators (294 authors)

45 Institutions

9 Countries:

Brazil, China, England, France, Germany, India, Poland, Russia, US


STARHBT

Geometry of STAR

ZCal

Barrel EM Calorimeter

Endcap Calorimeter

Magnet

Coils

TPC Endcap & MWPC

ZCal

FTPCs

Vertex Position Detectors

Central Trigger Barrel or TOF

Time Projection Chamber

Silicon Vertex Tracker

RICH


STARHBT

Au on Au Event at CM Energy ~ 130 AGeV

Event Taken June 25, 2000.


STARHBT

Particle ID in STAR

pion

s

kaons

pro

tons

deute

rons

electrons

STAR

dE/dx

dE/dx PID range: (dE/dx) = .08]

p ~ 0.7 GeV/c for K/

~ 1.0 GeV/c for p/p

RICH PID range:

1 - 3 GeV/c for K/

1.5 - 5 GeV/c for p/p

RICH

“kinks”:

K +

Vo

Decay vertices

Ks + + - p + -

p + + - + -

+ + + + K -

Topology CombinatoricsKs + + - K + + K -

p + - p + +

+ + - p + -

from K+ K- pairs

K+ K- pairs

m inv

m inv

same event dist.mixed event dist.

background subtracted

dn/dm

dn/dm


STARHBT

Kaon Spectra at Mid-rapidity vs Centrality

Exponential fits to mT spectra: ⎟⎠

⎞⎜⎝

⎛−∝T

mA

dm

dN

mT

TT

exp1

K+ K- (K++K-)/2

Ks

STAR preliminary STAR preliminary STAR preliminary

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

Good agreement betweendifferent PID methods


STARHBT

Hadrochemistry: particle yields vs statistical models


STARHBT

lattice QCD applies


STARHBT

Already producing QGP at lower energy?

Thermal model fits to particle yields(including strangeness, J/) approach QGP at CERN?

• is the system really thermal?• warning: e+e- falls on similar line!!

• dynamical signatures? (no)• what was pressure generated?• what is Equation of State of strongly-interacting matter?

Must go beyond chemistry: study dynamics of system well into deconfined phase (RHIC)

lattice QCD applies


STARHBT

Collision dynamics - several timescales

initial state

pre-equilibrium

QGP andhydrodynamic expansion

hadronic phaseand freeze-out

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Chemical freeze outKinetic freeze out

“end result” looks very similar whether a QGP was formed or not!!!

low-pT hadronic observables

hadronization

1 fm/c ? 5 fm/c ? 10 fm/c ? 50 fm/c ? time

dN/dt

“temperature”


STARHBT

First RHIC spectra - an explosive source

data: STAR, PHENIX, QM01model: P. Kolb, U. Heinz

• various experiments agree well

• different spectral shapes for particles of differing mass strong collective radial flow

mT1/m

T d

N/d

mT

light

heavyT

purely thermalsource

explosivesource

T,mT1/

mT d

N/d

mT

light

heavy• very good agreement with hydrodynamic

prediction


STARHBT

Hydrodynamics: modeling high-density scenarios

• Assumes local thermal equilibrium (zero mean-free-path limit) and solves equations of motion for fluid elements (not particles)

• Equations given by continuity, conservation laws, and Equation of State (EOS)

• EOS relates quantities like pressure, temperature, chemical potential, volume– direct access to underlying physics

• Works qualitatively at lower energybut always overpredicts collectiveeffects - infinite scattering limitnot valid there– RHIC is first time hydro works!

lattice QCD input


STARHBT

“Blast wave” Thermal motion superimposed on radial flow (+

geometry)Hydro-inspired “blast-wave” thermal freeze-out fits to , K, p,

)0 ,sinh ,(cosh )0,,( rezrtu ==

= −tanh 1r )( rfsr =

R

s

E.Schnedermann et al, PRC48 (1993) 2462

Tth = 107 MeV = 0.55

preliminary

M. Kaneta


STARHBT

• Momentum-space characteristics of freeze-out appear well understood

• Coordinate-space ?• Probe with two-particle intensity interferometry (“HBT”)

The other half of the story…


STARHBT

“HBT 101” - probing source geometry

2

21

2121 )q(~1

)p(P)p(P)p,p(P

)p,p(C +== C (Qinv)

Qinv (GeV/c)

1

2

0.05 0.10

Width ~ 1/R

Measurable! F.T. of pion source

222111 p)xr(i22

p)xr(i11T e)p,x(Ue)p,x(U

rrrrrr rrrr ⋅−⋅−=

5 fm

1 m source(x)

r1

r2

x1

x2

{2

1

}e)p,x(Ue)p,x(U 212121 p)xr(i21

p)xr(i12

rrrrrr rrrr ⋅−⋅−+

p1

p2

12 ppqrrr −=

1-particle probability(x,p) = U*U

( ))xx(iq2

*21

*1T

*T

21e1UUUU −⋅+⋅⋅=ψψ

2-particle probability


STARHBT

“HBT 101” - probing the timescale of emission

K

( ) ( ) ( )( ) ( )( ) ( ) ( )Kt~x~KR

Kx~KR

Kt~x~KR

2llong

2l

2side

2s

2out

2o

rr

rr

rr

β−=

=

β−= ⊥

xxx~ −≡

∫∫

⋅⋅⋅

≡)K,x(Sxd

)x(f)K,x(Sxdf

4

4

RoutRside ( ) ( )y,xx,x sideout ≠

Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentumqSide : qLong & qOut

(beam is into board)( )22

s2o RR τ⋅β+=

beware this “helpful” mnemonic!

( )2l

2l

2s

2s

2o

2o RqRqRq

lso e1)q,q,q(C ++−⋅λ+=


STARHBT

Large lifetime - a favorite signal of “new” physics at RHIC

• hadronization time (burning log) will increase emission timescale (“lifetime”)

• magnitude of predicted effect depends strongly on nature of transition

• measurements at lower energies (SPS, AGS) observe <~3 fm/c

“”

withtransition

c

Rischke & GyulassyNPA 608, 479 (1996)

3D 1-fluid Hydrodynamics

~

…but lifetime determination is complicated by other factors…


STARHBT

First HBT data at RHIC

STAR Collab., PRL 87 082301 (2001)

( )2l

2l

2s

2s

2o

2o RqRqRq


Data well-fit by Gaussian parametrization

Coulomb-corrected(5 fm full Coulomb-wave)

“raw” correlation function projection

1D projections of 3D correlation functionintegrated over 35 MeV/cin unplotted components


STARHBT

HBT excitation function

STAR Collab., PRL 87 082301 (2001)

•decreasing parameter partially due to resonances

•saturation in radii

•geometric or dynamic (thermal/flow) saturation

•the “action” is ~ 10 GeV (!)

•no jump in effective lifetime

•NO predicted Ro/Rs increase(theorists: data must be wrong)

•Lower energy running needed!?

midrapidity, low pT -

from central AuAu/PbPb


STARHBT

Central collision dynamics @ RHIC

• Hydrodynamics reproduces p-space aspects of particle emission up to pT~2GeV/c (99% of particles) hopes of exploring the early, dense stage

Heinz & Kolb, hep-th/0204061


STARHBT

Central collision dynamics @ RHIC

• Hydrodynamics reproduces p-space aspects of particle emission up to pT~2GeV/c (99% of particles) hopes of exploring the early, dense stage

• x-space is poorly reproduced• model source is too small and lives too

long and disintegrates too slowly?• Correct dynamics signatures with wrong

space-time dynamics?• The RHIC HBT Puzzle


• Is there any consistent way to understand the data?

• Try to understand in simplest way possible


STARHBT

Blastwave parameterization:Implications for HBT: radii vs pT

Assuming , T obtained from spectra fits strong x-p correlations, affecting RO, RS differently

pT=0.2

pT=0.4

( )22S

2O RR τ⋅β+=

K

KRS

RO

“whole source” not viewed


STARHBT

Blastwave: radii vs pT

STAR data

blastwave: R=13.5 fm, freezeout=1.5 fm/c

Using flow and temperature from spectra, can account for observed drop in HBT radii via x-p correlations, and Ro<Rs

…but emission duration must be small

Four parameters affect HBT radii

pT=0.4

pT=0.2

K

K

222s

2o RR +=


STARHBT

From Rlong: tkinetic = 8-10 fm/c (fast!)Simple Sinyukov formula

– RL2 = tkinetic2 T/mT

tkinetic = 10 fm/c (T=110 MeV)

B. Tomasik (~3D blast wave) tkinetic = 8-9 fm/c


STARHBT

hydro evolution

• Dynamical models:• x-anisotropy in entrance channel p-space anisotropy at freezeout

• magnitude depends on system response to pressure

Noncentral collision dynamics

φ= 2cosv2

( )φ+φ

2cosv21~d

dN2or


STARHBT

hydro evolution

• Dynamical models:• x-anisotropy in entrance channel p-space anisotropy at freezeout

• magnitude depends on system response to pressure

Noncentral collision dynamics

• hydro reproduces v2(pT,m) (details!)

@ RHIC for pT < ~1.5 GeV/c

• system response EoS• early thermalization indicated

Heinz & Kolb, hep-ph/0111075


STARHBT

hydro evolution later hadronic stage?




Effect of dilute stage

• dilute hadronic stage (RQMD):• little effect on v2 @ RHIC

Teaney, Lauret, & Shuryak, nucl-th/0110037

SPS

RHIC


STARHBT






• dilute hadronic stage (RQMD):• little effect on v2 @ RHIC• significant (bad) effect on HBT radii

calculation: Soff, Bass, Dumitru, PRL 2001

STARPHENIX

hydro onlyhydro+hadronic rescatt


STARHBT







• related to timescale? - need more info



STARHBT







• related to timescale? - need more info• qualitative change of freezeout shape!!

• important piece of the puzzle!

in-plane-extended

out-of-plane-extended



STARHBT

Possible to “see” via HBT relative to reaction plane?

p=0°

p=90°

Rside (large)

Rside (small)• for out-of-plane-extended source, expect• large Rside at 0• small Rside at 90

2nd-orderoscillation

Rs2 [no flow expectation]

p


STARHBT

“Traditional HBT” - cylindrical sources(reminder)

K

( ) ( ) ( )( ) ( )( ) ( ) ( )Kt~x~KR

Kx~KR

Kt~x~KR

2llong

2l

2side

2s

2out

2o

rr

rr

rr

β−=

=

β−= ⊥

xxx~ −≡

∫∫

⋅⋅⋅

≡)K,x(Sxd

)x(f)K,x(Sxdf

4

4RoutRside

( ) ( )y,xx,x sideout ≠

Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentumqSide : qLong & qOut

(beam is into board)

( )2l

2l

2s

2s

2o

2o RqRqRq



STARHBT

Anisotropic sources Six HBT radii vs

•Source in b-fixed system: (x,y,z)•Space/time entangled in

pair system (xO,xS,xL)

out

p

b

K

side

x

y

φ−−φ−=

+−φ−+φ−=

φ−φ+φ−+φ=

+−=

φ−φ−φ−+φ+φ=

φ−φ+φ=

⊥⊥

⊥⊥

⊥⊥⊥

sin)t~x~z~x~(cos)t~y~z~y~(R

t~t~z~sin)t~y~z~y~(cos)t~x~z~x~(R

cost~y~sint~x~2sin)x~y~(2cosy~x~R

t~t~z~2z~R

2siny~x~sint~y~2cost~x~2t~siny~cosx~R

2siny~x~cosy~sinx~R

LL2sl

2LLL

2ol

22212

os

22LL

22l

2222222o

22222s

!• explicit and implicit (xx()) dependence on

xxx~ −≡

∫∫

⋅⋅⋅

≡)K,x(fxd

)x(q)K,x(fxdq

4

4

Wiedemann, PRC57 266 (1998).


STARHBT

Symmetries of the emission functionI. Mirror reflection symmetry w.r.t. reactionplane (for spherical nuclei):

),,;,,,(S),,;,,,(S Φ−−=Φ TT KYtzyxKYtzyx

),,(~~),,(~~1 Φ−⋅θ=Φ TT KYxxKYxx

with 22)1(1 δ+δ−=θ

II. Point reflection symmetry w.r.t. collision center (equal nuclei):

),,;,,,(S),,;,,,(S +Φ−−−−=Φ TT KYtzyxKYtzyx

),,(~~),,(~~2 +Φ−⋅θ=Φ TT KYxxKYxx

with 00)1(2 δ+δ−=θ

Heinz, Hummel, MAL, Wiedemann, nucl-th/0207003


STARHBT

Fourier expansion of HBT radii @ Y=0Insert symmetry constraints of spatial correlation tensor into Wiedemann relations and combine with explicit Φ-dependence:

∑∑∑∑∑∑

=

=

=

=

=

=

φ⋅⋅=φ

φ⋅⋅=φ

φ⋅⋅+=φ

φ⋅⋅=φ

φ⋅⋅+=φ

φ⋅⋅+=φ

,...5,3,12

,2

,...5,3,12

,2

,...6,4,22,

20,

2,...6,4,2

2,

2,...6,4,2

2,

20,

2,...6,4,2

2,

20,

2

)sin(2)(

)cos(2)(

)cos(2)(

)sin(2)(

)cos(2)(

)cos(2)(

n nslsl

n nolol

n nlll

n nosos

n nooo

n nsss

nRR

nRR

nRRR

nRR

nRRR

nRRR

Note: These most general forms of the Fourier expansions for the HBT radii are preserved when averaging the correlation function over a finite, symmetric window around Y=0.

Relations between the Fourier coefficients reveal interplay between flow and geometry, and can help disentangle space and time

Heinz, Hummel, MAL, Wiedemann, nucl-th/0207003


STARHBT

xout

xside

K

Anisotropic HBT results @ AGS (s~2 AGeV)

p (°) 0 180

0

0 180 0 180

10

-10

20

40

R2 (

fm2 ) out side long

ol os sl

Au+Au 2 AGeV; E895, PLB 496 1 (2000)

• strong oscillations observed• lines: predictions for static (tilted) out-of-plane extended source

consistent with initial overlap geometry

p = 0°


STARHBT

xout

xside

K

Meaning of Ro2() and Rs

2() are clearWhat about Ros

2() ?

p (°) 0 180

0

0 180 0 180

10

-10

20

40

R2 (

fm2 ) out side long

ol os sl

Au+Au 2 AGeV; E895, PLB 496 1 (2000)

• Ros2() quantifies correlation between xout and xside

• No correlation (tilt) b/t between xout and xside at p=0° (or 90°)

K

x out x sid

e K x out x sid

e

K x out x side

K xout

x side

K xout

xside

K xout

xside

p = 0°p ~45°

• Strong (positive) correlation when p=45°

• Phase of Ros2() oscillation reveals orientation of extended source

No access to 1st-orderoscillations in STAR Y1


STARHBT

Indirect indications of x-space anisotropy @ RHIC

• v2(pT,m) globally well-fit by hydro-inspired “blast-wave”(Houvinen et al)

STAR, PRL 87 182301 (2001)

soliddashed

0.04 0.010.09 0.02a (c)

0.04 0.01 0.0S2

0.54 0.030.52 0.020(c)

100 24135 20T (MeV) temperature, radial flowconsistent with fits to spectra

anisotropy of flow boost

spatial anisotropy (out-of-plane extended)


STARHBT

STAR data Au+Au 130 GeV

minbias

2OR

2OSR

2SR

2LR

preliminary

• significant oscillations observed

• blastwave with ~ same parameters as used to describe spectra & v2(pT,m)

• additional parameters:

•R = 11 fm = 2 fm/c !!

full blastwave

consistent with R(pT), K-


STARHBT

2OR

2OSR

2SR

2LR

preliminary

full blastwave

STAR data Au+Au 130 GeV

minbias• significant oscillations observed

• blastwave with ~ same parameters as used to describe spectra & v2(pT,m)

• additional parameters:

•R = 11 fm = 2 fm/c !!

consistent with R(pT), K-

no spatial anisotropy

no flow anisotropy

• both flow anisotropy and source shape contribute to oscillations, but…

• geometry dominates dynamics

• freezeout source out-of-plane extended fast freeze-out timescale ! (7-9 fm/c)


STARHBT

Azimuthal HBT: hydro predictionsRHIC (T0=340 MeV @ 0=0.6 fm)

•Out-of-plane-extended source (but flips with hadronic afterburner)

• flow & geometry work together to produce HBT oscillations

•oscillations stable with KT


(note: RO/RS puzzle persists)


STARHBT

Azimuthal HBT: hydro predictions

“LHC” (T0=2.0 GeV @ 0=0.1 fm)

• In-plane-extended source (!)

•HBT oscillations reflect competition between geometry, flow

• low KT: geometry

•high KT: flowsign flip

RHIC (T0=340 MeV @ 0=0.6 fm)

•Out-of-plane-extended source (but flips with hadronic afterburner)

• flow & geometry work together to produce HBT oscillations

•oscillations stable with KT



STARHBT

HBT(φ) Results – 200 GeV

• Oscillations similar to those measured @ 130GeV

• 20x more statistics explore systematics in centrality, kT

• much more to come…

STAR PRELIMINARY


STARHBT

Kaon – pion correlations:dominated by Coulomb interaction

Smaller source stronger (anti)correlation

K-p correlation well-described by:

• Blast wave with same parameters as spectra, HBT

But with non-identical particles, we can access more information…

STAR preliminaryAdam Kiesel, Fabrice Retiere


STARHBT

Initial idea: probing emission-time ordering

• Catching up: cos0• long interaction time• strong correlation

• Ratio of both scenarios allow quantitative study of the emission asymmetry

• Moving away: cos0• short interaction time• weak correlation

Crucial point:kaon begins farther in “out” direction(in this case due to time-ordering)

purple K emitted firstgreen is faster

purple K emitted firstgreen is slower


STARHBT

measured K- correlations - natural consequence of space-momentum

correlations

• clear space-time asymmetry observed

• C+/C- ratio described by:– “standard” blastwave w/ no time shift

• Direct proof of radial flow-induced space-momentum correlations

Kaon <pt> = 0.42 GeV/c

Pion <pt> = 0.12 GeV/c

STAR preliminary


STARHBT

SummaryRHIC 130 GeV Au+Au

Disclaimer: all numbers (especially time) are rough estimates

Tomasik (3D blastwave): 8-9 fm/c (fit to PHENIX even smaller)Sinyukov formula: Rlong

2=2T/mT = 10 fm/c for T=110 MeVK-

K*


STARHBT

SummaryRHI – the only way to create/study deconfined colored matterHadrochemistry suggests creation of QGP @ RHIC (and SPS)Quantitative understanding of bulk dynamics crucial to extracting real physics at RHIC

• p-space - measurements well-reproduced by models• anisotropy [v2(pT,m)] system response to compression (EoS)

• x-space - generally not well-reproduced• anisotropy [HBT()] evolution, timescale information, geometry/flow interplay• Azimuthally-sensitive HBT: correlating quantum correlation with bulk correlation

• reconstruction of full 3D source geometry• relevant here: OOP freeze-out

Data do suggest consistent (though surprising) scenario• strong collective effects• rapid evolution, then emission in a “flash” (key input to models)• where is the hadronic phase?

• K-, HBT(pT), HBT(), K*…

By combining several (novel) measurements, STAR severely challenges our understanding of dynamics in the soft sector of RHIC


STARHBT

Backup slides follow

• Freezeout geometry out-of-plane extended• early (and fast) particle emission !• consistent with blast-wave parameterization of v2(pT,m), spectra, R(pT), K-

• With more detailed information, “RHIC HBT puzzle” deepens• what about hadronic rescattering stage? - “must” occur, or…?• does hydro reproduce t or not??

• ~right source shape via oscillations, but misses RL(mT)

• Models of bulk dynamics severely (over?)constrained


STARHBT

SummaryFreeze-out scenario f(x,t,p) crucial to understanding RHIC physics

• p-space - measurements well-reproduced by models• anisotropy system response to compression• probe via v2(pT,m)

• x-space - generally not well-reproduced• anisotropy evolution, timescale information• Azimuthally-sensitive HBT: a unique new tool to probe crucial information from

a new angle

elliptic flow data suggest x-space anisotropy HBT R() confirm out-of-plane extended source

• for RHIC conditions, geometry dominates dynamical effects• oscillations consistent with freeze-out directly from hydro stage (???)• consistent description of v2(pT,m) and R() in blastwave parameterization

• challenge/feedback for “real” physical models of collision dynamics


STARHBT

RHIC AGS

• Current experimental access only to second-order event-plane• odd-order oscillations in p are invisible

• cannot (unambiguously) extract tilt (which is likely tiny anyhow)• cross-terms Rsl

2 and Rol2 vanish @ y=0

concentrate on “purely transverse” radii Ro2, Rs

2, Ros2

• Strong pion flow cannot ignore space-momentum correlations• (unknown) implicit -dependences in homogeneity lengths geometrical inferences will be more model-dependent• the source you view depends on the viewing angle


STARHBT

Summary of anisotropic shape @ AGS

• RQMD reproduces data better in “cascade” mode

• Exactly the opposite trend as seen in flow (p-space anisotropy)

• Combined measurement much more stringent test of flow dynamics!!

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STAR HBT 4 oct 2002malisa - seminar IUCF1 Two-particle correlations and Heavy Ion Collision Dynamics...

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