aa versus pp (& da): a puzzling scaling in hbt@rhic

February 2005 lisa - XXI Winter Workshop - Breckenridge CO 1

AA versus pp (& dA):A puzzling scaling in HBT@RHIC

Zbigniew Chajęcki1, Tom Gutierrez2,

Mike Lisa1, Mercedes López-Noriega1

1 Ohio State University2 U.C. Davis, LBL


Outline

• Indispensability of spacetime in RHI studies

• Femtoscopy in RHI collisions (rhic)– Rationality of systematics [important reminder]

– The “puzzle” [refresher of one aspect]

• Focus on mT (T) systematic

– Underlying physics in AA: dynamically-driven geometric substructure

– Do we understand AA relative to pp (and dA)?

– If not, what is the matter?!

• Not-really-a-conclusion


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


qout

qside

qlong

Hanbury Brown-Twiss interferometry

Rsi

de

R long

Rout

x1

x2

12 ppqrrr −=

p1

p2

qr

( )12 pp2

1k

rrr+=

• Two-particle interferometry: p-space separation space-time separation

• HBT: Quantum interference between identical particles

pairsevent mixed

pairsevent real

)(P)(P

),(P),(

21

2121 ==

pppp

ppC

2long

2long

2side

2side

2out

2out)(1),(

RqRqRqekkqC

−−−λ+=vrr

q (GeV/c)q (GeV/c)

C (

q)C

(q)

11

22R

1~

– Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for

Gaussian model (3-d):


qout

qside

qlong

Hanbury Brown-Twiss interferometry

Rsi

de

R long

Rout

x1

x2

12 ppqrrr −=

p1

p2

qr

( )12 pp2

1k

rrr+=

• Two-particle interferometry: p-space separation space-time separation

RRsideside

RRoutout


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 (neglected?) 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

Systematic decadence

• 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”


Systematic decadence

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

‘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

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

r

y

|b|

pT


Does HBT in rhic make sense?

YES…

Size [R(Npart1/3)]

Shape [R( )]

mor

e ce

ntra

l

STAR, PRL93 012301 (2004)



YES…

Size [R(Npart1/3)]

Shape [R( )]

? Dynamic substructure [R(mT)]


Why do the radii fallwith increasing momentum ??


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)

1500 fm/c (!)



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 v) 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, Phys. Rev. C70 044907 (2004)

pT

T

K

p


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 v) 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

x

(fm

)

x (

fm)

T T



YES…

Size [R(Npart1/3)]

Shape [R( )]

Dynamic structure [R(mT)] A. Kisiel (STAR) QM04

x

(fm

)

x (

fm)



YES…

Size [R(Npart1/3)]

Shape [R( )]

Dynamic structure [R(mT)]

… and NO

? Model disagreement [transport]

Heinz & Kolb, WW18 hep-ph/0204061



YES…

Size [R(Npart1/3)]

Shape [R( )]


… and NO


? Too-short timescales [BW]

F. Retiere & MAL, Phys. Rev. C70 044907 (2004)F. Reiere, QM04 nucl-ex/0405024

T=106 MeV; <> = 0.55; R = 12.5 fm

Lifetime () = 8.4 ± 0.2 fm/c

Emission duration () = 1.9 ± 0.2 fm/c



YES…

Size [R(Npart1/3)]

Shape [R( )]


… and NO


? Too-short timescales [BW]

T=106 MeV; <> = 0.55; R = 12.5 fm

Lifetime () = 8.4 ± 0.2 fm/c

Emission duration () = 1.9 ± 0.2 fm/c

RY

RX

t = 0“initial”

t = “final”

BW fits: flow velocity max()• at edge• at freezeout

Surely… R(,t=) < R(,t=0) + max()*

€

R − Rinitial = βT ,max ⋅τ

STAR nucl-ex/0411036 [subm PRC]



YES…

Size [R(Npart1/3)]

Shape [R( )]


… and NO


? Too-short timescales [BW]? Inconsistent dynamical picture

€

R − Rinitial = βT ,max ⋅τ

STAR nucl-ex/0411036 [subm PRC]

RY

RX

t = 0“initial”

t = “final”



YES…

Size [R(Npart1/3)]

Shape [R( )]


… and NO



? No large rise in RO, RL [general]



YES…?

Size [R(Npart1/3)]

Shape [R( )]


… and NO



? No large rise in RO, RL [general]

Simultaneously reasonable?

€

HBT( s;pT ,y,r b , ˆ b ,m1,m2,Asys)


T s1b y2 sˆHBT( ; , y, b , ,m ,m , )p As φr

• latest “puzzle” in HBT?

• HBT radii from pp fall with pT

(as observed previously, usually attributed to string kT kick)…

• …but as much (proportionally) as dAu and AuAu ??• coincidence…?• something deeper…?

Rout

Rside

Rlong

p+p+X

pT

0.25 0.5

2

1

STAR, QM04

Rout / Rout(pp) Rside / Rside(pp)

Rlong / Rlong(pp)

Au+AuCollective expansion

p+pstring fragmentation

transverse plane







• What it does NOT mean:• AA=N*(strings)• AA=N*(“little blastwaves”)

• AA: global x-p correlations

localx-p corr.

NB: p-space observables identical in the two cases









localx-p corr.



Focus on RLONG

• Sinyukov: Boost-invariant:

(+ flow effects) qout

qside

qlong

Rsi

de

R long

Rout

x1

x2

p1

p2

qr

( )12 pp2

1k

rrr+=

€

RL(mT ) = τ 0 ⋅T

mT

€

×K2 mT /T( )K1 mT /T( )


Focus on RLONG


(+ flow effects)

• Au+Au - reasonable

– But* hydro alone : 0~15 fm/c€

RL(mT ) = τ 0 ⋅T

mT

€

×K2 mT /T( )K1 mT /T( )

* Heinz & Kolb, hep-ph/0204061 NparticipantsSTAR nucl-ex/0411036 [subm PRC]

February 2005 lisa - XXI Winter Workshop - Breckenridge CO 31* Heinz & Kolb, hep-ph/0204061

Focus on RLONG


(+ flow effects)

• Au+Au - reasonable

– But* hydro alone : 0~15 fm/c

• In p+p (e+e): often understood

via Heisenberg

• Identical experimental behavior

• VERY different physics ! (right?)

€

RL(mT ) = τ 0 ⋅T

mT

€

×K2 mT /T( )K1 mT /T( )

€

RL(mT ) = c ⋅h ⋅τ 0

mT

K p,

RZ (

fm)

R (

fm)

mT (GeV)

m (GeV)

G. Alexanderhep-ph/0108194Hadronic Z0 decays

~ 1 fm/c


“Geometrical” RS

• AA “understood” (?) in terms of

collective flow

• “Spooky” that pp ~ AA/5

• But…

pp, dAu apparent global x-p

correlations, but no expansion?– p+p fair comparison?

RY

RX

t = 0“initial”

t = “final”

F. Retiere, QM04


Bummer…• pp = “little AA” physics-wise ?

– hey, why not? (Csorgo)

• different driving physics just looks the same ? [coincidence]– resonances (Wiedemann, Schlei,…)– uncertainty principle morphs (weirdly) into thermal/collective scenario?– “kicks” in string-breaking dynamics

• HBT just doesn’t measure geometry/dynamics anyway– because it doesn’t work (Gyulassy, based on convenience)– source<--> HBT not so simple (Kapusta, Wong,Cramer…)– it cannot be that wrong (Lisa, based on systematics)

• It it our oversimplified Gaussian radii?


Worst-case picture of d-Au [prelim]

• 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?

(indep of Gaussian ansatz)– ad hoc “fixes” dangerous!

• Problem with projections– cannot see systematics in 3D

– experiments w/same CF will have different projections

QuickTime™ and aTIFF (Uncompressed) decompressor


STAR Prelim

inary


Whole CF at a glance• 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]

• ~immune to acceptance

• full information content at a glance[thanx to symmetries]






L=0 L=2 L=4

M=0

M=2

M=4

Simple, Gaussiansource calculations

RL < RT

RL > RT

RO < RS

RO > RS

“Rinv”But better!!

~acceptance free!


L=0 L=2 L=4

M=0

M=2

M=4

Gaussian source fit(Coulomb in fit)

d+Au kT-integrated

RO = 1.74 fmRS = 1.69 fmRL = 2.14 fmλ= 0.36

data

STAR Prelim

inary


Mike’s shortest summary ever(let’s discuss)

• Along most axes, HBT systematics make sense– it’s the geometry, stupid & geometry defines R.H.I.C.

– so, take “puzzles” seriously

• recent “puzzle”: pp/dA/AA HBT versus mT “too similar”

– timescales from RL? Heisenberg or Boost-invariant thermal bulk?

– dynamically-induced RS(mT)? pp = “little AA”?

• is lack of expansion in pp comforting? Is pp valid reference?

– insensitivity of HBT to different underlying physics?

– fitting artifact? Ylm decomp (+ imaging) promising & underway

• IMHO* : issues with data but they are not the root cause (also Gaussian is not at root)

* IMHO = In Mike’s Humble Opinion


Is this what we’ve come (back) to?

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

R = 1.2 (fm)•A1/3

Take the problem seriously,

and nobody gets hurt


The end









localx-p corr.


aa versus pp (& da): a puzzling scaling in hbt@rhic

Documents

understanding of

dynamicsintermediate

exciting signalsfinal

hallmark of rhicinitial

detailed understanding

impt element

sourcecombo of x

tp correlationsearly