femtoscopy in heavy ion collisions: two decades of progress

mike lisa - Femtoscopy in relativistic heavy ion collisions - WPCF Aug 2005 - Kroměříž Czech Republic 1

Femtoscopy in heavy ion collisions:Two decades of progress

Mike Lisa

Ohio State University

An experimentalist’s view of the situation B.Q.M.(*)cf. Bysterský, Chajecki, Chaloupka, Chung, Kisiel, Kniege, Panitkin...

* BQM= Before Quark Matter


Outline

• Relevance of femtoscopy to R.H.I.C.

• Growing activitiies of a (sub)field : 2 decades of systematics

• R(√SNN, b, Npart, A, B, mT, y, , PID)• what information is encoded?• what have we mined so far?• special attention to size and shape

• comments

blastwave

comparison to modelsexperimental details


Spacetime - an annoying bump on the road to Stockholm?

• Non-trivial space-time - the hallmark of rhic• Initial state: dominates further dynamics• Intermediate state: impt element in exciting signals• Final state:

• Geometric structural scale is THE defining feature of QGP

STAR, PRC66 (2002) 034904 STAR, PRL93 (2004) 252301


Spacetime - an annoying bump on the road to Stockholm?

• Non-trivial space-time - the hallmark of rhic• 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 (?)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Ann.Rev.Nucl.Part.Sci. 46 (1996) 71


A.D. Chacon et al, Phys. Rev. C43 2670 (1991)G. Alexander, Rep. Prog. Phys. 66 481 (2003)

R = 1.2 (fm)•A1/3

Two decades of systematics

• Pion HBT @ Bevalac: “largely confirming nuclear dimensions”• Since 90’s: increasingly detailed understanding and study w/ high stats

)s(HBT

‘85 ‘90 ‘95 ‘00 ‘05

5

10

15

20AGS/SPS/RHIC HBT papers (expt)

Bo

al/

Je

nn

ing

s/G

elb

ke

Heinz/JacakWiedemann/Heinz

Csorgo

To

ma

sik

/Wie

de

ma

nn

“R = 5 fm”


Two decades of systematics

• Pion HBT @ Bevalac: “largely confirming nuclear dimensions”• Since 90’s: increasingly detailed understanding and study w/ high stats

T 1 2 sysˆHBT( ;p , y, b ,b,ms ,m ,A )

r

y

|b|

pT

‘85 ‘90 ‘95 ‘00 ‘05

5

10

15

20AGS/SPS/RHIC HBT papers (expt)

Bo

al/

Je

nn

ing

s/G

elb

ke

Heinz/JacakWiedemann/Heinz

Csorgo

To

ma

sik

/Wie

de

ma

nn


Forget homogeneity regions or fancy stuff.

Do femtoscopic length scales increase when they “should?”

Also• SPS [NA44(‘99),NA49(‘00)]• RHIC [STAR(‘05)]

Repeating most basic sanity check at relativistic energies...

p-p correlations

* big bump small source


ˆT 1b ys2 sHBT( ;p , y, ,b ,m ,m ,A )s φr

•Generalize A1/3 Npart1/3

•not bad @ RHIC!•connection w/ init. size?

Varying initial “source size”

Fixed A+B : vary b

Fixed b : vary A (& B!)

Likely scaling variable: Npart

b

PHENIX, PRL 2004

Au+Au sNN =200 GeV


•Generalize A1/3 Npart1/3

•not bad @ RHIC!•connection w/ init. size?

•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 GeV)

ˆT 1b ys2 sHBT( ;p , y, ,b ,m ,m ,A )s φr

PHOBOS

LPSW nucl-ex/0505014

NB: not constant density


We are not alone...

H. Caines (STAR) QM05

Tounsi, Mischke, RedlichNPA715 565 (2003)

H. Caines (STAR) QM05

NA57 (open)STAR (filled)

NA57 (open)STAR (filled)

S. Manly (PHOBOS) QM05

Entropy determines “everything” at bulk level (soft sector) ?

NB: scaling violated s < 4 GeV(as with femtoscopy)


Refinement: chemical effects

• different behaviour below/above AGS

• violates “universal” scaling

• baryon meson dominance

• neglect time/dynamics: gross F.O.

geometry appears determined by

• chemistry

• “universal” mean free path ~ 1 fm (!?)

fm 1~ ⇒==σσ

ρλ

NVff

fm.f.p

2sidelong

2/3)2( RRV f π≡~ FO volume

∑ +=≡i

NNii NNNN πππππ σσσσx-section:

Vf

Nσ

CERES, PRL 90 (2003) 022301


Messages from systematics• AB, |b|, Npart systematics

• sanity check on overall size dependence • final state multiplicity/chemistry determines rough geometry...

c.f. Chajecki - lighter systems

collective/flow-like expansion? probe anisotropically!

...and that geometry is ~2x initial size


Strongly-interacting 6Li released from an asymmetric trapO’Hara, et al, Science 298 2179 (2002)

T ˆ 1 ysb 2 sHBT( ;p , y, b , ,m ,m ,A )s φr

What can we learn?

in-plane-extended

out-of-plane-extended

Teaney, Lauret, & Shuryak nucl-th/0110037

transverse FO shape+ collective velocity evolution time estimate

check independent of RL(pT)

?


• observe the source from all angles

with respect to RP• expect oscillations in HBT radii

big RS

small RS



• observe the source from all angles

with respect to RP• expect oscillations in HBT radii

(including “new” cross-terms)

out

side

out

side

R2out-side<0

when pair=135º



STAR, PRL93 012301 (2004)Measured final source* shape

* model-dependent, but see Retiere & MAL PRC70 044907 2004

R2out-side<0

when pair=135º


ever see that symmetry at ycm ?


STAR, PRL93 012301 (2004)

centralcollisions

mid-centralcollisions

peripheralcollisions

Measured final source* shape


* model-dependent, but see Retiere & MAL PRC70 044907 2004

Expected evolution:


Evolution of size and shape - “the rule of two”

€

R s;pT ,y,r b ,AB,φˆ b

,m1,m2( )

initi

al= fin

al

STAR PRL93 012301 (2004)

Initial size/shape estimated by Glauber calculationFinal config according to Retiere & MAL PRC70 044907 2004

~ x2 size increase ~ 1/2 shape reduction

c.f. Chajecki - lighter systems

2x

2y

2x

2y

RR

RR

+−

≡


• non-trivial excitation function• does it make sense? Is it

related to bulk dynamics? YES

sNN (GeV)

(approximately same centrality)

AGS: FO init

RHIC: FO < init

“Anisotropic sanity check”

€

Δ ≈β ⊗ v2 ⊗ τ ???

is relation b/t final and near quantitatively sensible?


A simple estimate – 0 from init and final

0Y,XY,X

t.)O.F()t(

ββ ⋅=→

“radial flow”

P. Kolb, nucl-th/0306081

• BW → βX, βY @ F.O. (βX > βY)

• hydro: flow velocity grows ~ t

• From RL(mT): 0 ~ 9 fm/c

consistent picture• Longer or shorter evolution times

X inconsistent

toy estimate: 0 ~ 0(BW)~ 9 fm/c

• too short to account for expansion??

• Need a real model comparison→ asHBT workable “evolutionary clock” constraint for models MAL ISMD03


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 v2

• ...flow is defined by space-momentum correlations

only femtoscopy can probe substructureof dynamic bulk behaviour


Spectra

v2

HBT

Flow-dominated“Blast-wave” modelPRC70 044907 (2004)


ˆ 1 2 sysbTHBT( ; , y, b , ,m ,m ,A )ps φr

Kolb & Heinz, QGP3 nucl-th/0305084

Decreasing R(pT)

• 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



Decreasing R(pT)




Non-flow possibilities• cooling, thermally (not collectively)

expanding source

• combo of x-t and t-p correlationsearly times: small, hot source

late times: large, cool source



Decreasing R(pT)





expanding source

• combo of x-t and t-p correlations

MAL et al, PRC49 2788 (1994)



Decreasing R(pT)





expanding source


• hot core surrounded by cool shell

• important ingredient of Buda-Lund hydro picturee.g. Csörgő & LörstadPRC54 1390 (1996)



Decreasing R(pT)





expanding source


• hot core surrounded by cool shell

• important ingredient of Buda-Lund hydro picturee.g. Csörgő & LörstadPRC54 1390 (1996)

t

Each scenario generatesx-p correlations but…

x2-p correlation: yesx-p correlation: yes

x2-p correlation: yesx-p correlation: no

x2-p correlation: yesx-p correlation: no



• flow-dominated “models” can reproduce soft-sector x-space observables

• imply short timescales

• however, are we on the right track? [flow]• puzzles? check your assumptions!• look for flow’s “special signature”

x-p correlation

• In flow pictures, low-pT particles emitted closer to source’s center (along “out”)

• non-identical particle correlations(FSI at low Δv) probe:

(x1-x2)2 (as does HBT)

x1-x2

Csanád, Csörgő, Lörstad nucl-th/0311102 and nucl-th/0310040

[click for more details on non-id correlations]

F. Retiere & MAL, nucl-th/0312024

pT

βT

K

p

π


ˆT 2 sysb 1HBT( ;p , y, b , m ,m, ,A )s φr

• In flow pictures, low-pT particles emitted closer to source’s center (along “out”)

• non-identical particle correlations(FSI at low Δv) probe:

(x1-x2)2 (as does HBT)

x1-x2

• extracted shift in emission point x1-x2 consistent w/ flow-dominated blastwave

A. Kisiel (STAR) QM04

Δx

(fm

)Δ

x (

fm)

βT βT



QM02


RHIC femtoscopy with wide variety of particle species

π+ π- K+ K- K0S p p

π+

π-

- K+

K-

- - K0S

p

p

R(√SNN, b, Npart, A, B, mT, y, , PID1, PID2)

= prelim or final result available


Strong flow confirmed by all expts...

€


,m1,m2( )LPSW(05) - DATA in color-- experimentalist’s plot

what agreement!! (what agreement?)


€


,m1,m2( )

€

R i mT( ) =′ R i

mTα i

Strong flow confirmed by all expts...

Central (~10%) AuAu (PbPb) collisions at y~0


Another implication of strong flow: ~mT scaling

€


,m1,m2( )


Motivation Formalism Experiment Trends Models

Some longitudinal systematics

€


,m1,m2( )

cons

istent w

ith bo

ost-inva

riance



inconsis

tent with

boost-inva

riance

PHOBOS nucl-ex/0410022


beam

“Dynamic” BI without “Chemical” BI ?Only femtoscopy can tell!


qX (GeV/c) qY (GeV/c) qZ (GeV/c)

C

E877, Miskowiec CRIS’98 nucl-ex/9808003

p-π-

Greater detail - π-p correlations @ AGS

€


,m1,m2( )



sizes and offsets in impact parameterand longitudinal directions

b

z

10 fm


Comments• massive systematic program provides tremendous geometric detail

• each element reasonable by itself not really “puzzling.”

• “critical mass” in the femtoscopy community• Related, but not in my talk: important new directions [talks @ WPCF]

• moments analysis• imaging• continued emphasis on non-identical particle correlations• connection to “elementary” systems - communication “across lines”

• Important puzzles beyond central Au+Au at top energy

• Ignoring femtoscopy to pursue “perfection” is unjustified• Space-time is the defining feature of R.H.I.C.• Femtoscopy does measure space-time• The measurements are sensitive to underlying physics

We are working on the many slowly crawling ants...We are working on the many slowly crawling ants...

... don’t give up your dreams!!... don’t give up your dreams!!

femtoscopy in heavy ion collisions: two decades of progress

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