A menu of expectations for femtoscopy * 1.0 at LHC /ALICE

Mike Lisa - ISMD, Berkeley - August 2007 1

A menu of expectations forfemtoscopy* 1.0 at

LHC/ALICEMike Lisa

Ohio State University

* femtoscopy (fem-ta-skö-pee) nounThe measurement of spatial scales at the fermi level.Non-trivially related to the “HBT effect” invented to measure stellar scales


Outline

• Brief motivation / review

• Model expectations for H.I. collisions [ mostly]

• The importance of femtoscopy in p+p collisions

• A menu


Microexplosions Femtoexplosions

s 0.1 J 1 J

1017 J/m3 5 GeV/fm3 = 1036 J/m3

T 106 K 200 MeV = 1012 K

rate 1018 K/sec 1035 K/s

• fast energy deposition plasma

hydro expansion cooling to original phase

• do geometric “postmortem” & infer momentum



s 0.1 J 1 J

1017 J/m3 5 GeV/fm3 = 1036 J/m3

T 106 K 200 MeV = 1012 K







s 0.1 J 1 J

1017 J/m3 5 GeV/fm3 = 1036 J/m3

T 106 K 200 MeV = 1012 K





measure explosive pattern of the thermalized bulk matter (low-pT)

B2B jets?

access to bulk properties (EoS) driving dynamics


Spectra

v2

HBT


hydro expectation(off-center collision)

collective pT component: m*vT


Spectra

v2

HBT


“elliptic flow”


Spectra

v2

HBT


femtoscopyprobes x-psubstructure


hydro

ideal fluid dynamics

At RHIC: Explosive signature sensitive to physics in models

cascade

Boltzmann models

- collisions between particles

3 talks later

What might we expect at LHC?


“All” soft-physics observables at RHIC (& often SPS/AGS)

are multiplicity-driven

S. Manly (PHOBOS) QM05

H. Caines (STAR) QM05

NA57 (open)STAR (filled)

NA57 (open)STAR (filled)

G. Westfall, WPCF 2007

E-by-E fluctuation in K/

MAL,Pratt Soltz,Wiedemann nucl-ex/0505014

Entropy dominance?


PHOBOS White Paper: NPA 757, 28

1000 5.5 TeV

5

6

6.4 = RHICx1.6


NNUS*: Multiplicity sets scale: all else fixed

• PHOBOS-based extrapolation:•RLHC / RRHIC = (1.6)1/3 = 1.17

PHOBOS White Paper: NPA 757, 28

1000 5.5 TeV

5

6

6.4 = RHICx1.6

* NNUS = Nothing New Under the Sun




• CGC prediction of multiplicity

•RLHC / RRHIC = (11/3.6)1/3 = 31/3 = 1.45

Kharzeev, Levin & Nardi NPA747 609 (2005)





•RLHC / RRHIC = (11/3.6)1/3 = 31/3 = 1.45

• R <~ 11 fm [low pT pions generate largest separation distribution]


ST

AR

PR

C71 044906 (2005)




•RLHC / RRHIC = (11/3.6)1/3 = 31/3 = 1.45

• R <~ 11 fm•well within experimental reach

•Rfit ~ 1/(q2)

•q ~ 1 MeV/c

•qmin ~ 2 MeV/c

ALICE PPR (vol 2): J. Phys G. Part. Nucl. Phys. 32 1295 (2006)

Access to low-q -> high R


Access to long-range non-Gaussian tail

• Generalized imaging* fit probes long-R / low-q

• access to resonance tail•small below s ~ 10 GeV•LHC should be ~RHIC

• (... and/or “other” tails...)

• details beyond gross size Brown, Soltz, Newby, Kisielnucl-th/0705.1337

PH

EN

IX, P

RL 98, 13

2301 (2007) ,

* c.f. talks of P. Danielewicz & P. Chung


Physics from (Gaussian) scales - dynamic models

• Boltzmann models•particle rescattering• thermalization not assumed• typically “hard” EoS

• softening must be put in by hand (“string melting” etc)

• Hydrodynamic models• thermalization / “perfect fluid”•EoS varied. Typically a “soft point” used


Boltzmann-type models

• Humanic/Hadron Rescattering Model

• “real” model predicting flow & HBT

• (dN/d[LHC] / dN/d[RHIC])1/3 ~ 1.9

dN

/d

T. Humanic,Int.J.Mod.Phys.E15197(2006)



Rlo

ng (

fm)

dN

/dt



• (dN/d[LHC] / dN/d[RHIC])1/3 ~ 1.9

• LHC / RHIC = 2 :: (recall Rlong~~ )

• dynamic effect

•Rlong[LHC] / Rlong[RHIC] ~ 2

• all are connected??






• (dN/d[LHC] / dN/d[RHIC])1/3 ~ 1.9


• dynamic effect


• all are connected?

•RS, RO larger, but not a simple factor






• (dN/d[LHC] / dN/d[RHIC])1/3 ~ 1.9


• dynamic effect


• all are connected?

•RS, RO larger, but not a simple factor

• steeper pT-dep due to more flow?

• dynamic effect

• Hard EoS rescattering models: dynamic effects superimposed on

chemistry•similar for AMPD C.M. Ko; WPCF06



Hydro predictions I: Scales• Neglecting flow, to cool to C[QGP] :

C = 0(C /0)3/4

• Cno flow[RHIC] = 6 fm/c

• Cno flow[LHC] = 20 fm/c

Eskola et al PRC72044904 (2005)

initial conditions frompQCD+saturation


• Neglecting flow, to cool to C[QGP] :

C = 0(C /0)3/4



• Much larger flow @LHC•signif. reduction of timescale @ LHC

[similar to RHIC]

• larger transverse size @ FO

Eskola et al PRC72044904 (2005)Hydro predictions I: Scales



C = 0(C /0)3/4




[similar to RHIC]


• No HBT prediction per se, but...

•RL[LHC] / RL[RHIC] ~ 1.1 ÷ 1.2

•RS[LHC] / RS[RHIC] ~ 1.5 ÷ 2

• (different than HRM)

•steeper pT-dependence




C = 0(C /0)3/4




[similar to RHIC]


• No HBT prediction per se, but...

•RL[LHC] / RL[RHIC] ~ 1.1 ÷ 1.2

•RS[LHC] / RS[RHIC] ~ 1.5 ÷ 2

• (different than HRM)

•steeper pT-dependence

• Consistent w/ independent hydrofor non-central collisions


Heinz&Kolb, PLB542 216 (2002)

(LHC)


• easy prediction: importance of -dep measurements will continue @ LHC• RP resolution at least as good as STAR

• asHBT• measures source shape at freezeout

Hydro predictions II: Shapes

STAR 200 GeV

PRL93 012301 (‘04)




• asHBT• measures source shape at freezeout• probes timescale & dynamics• non-trivial (& incomplete!) excitation fctn


E895 2 GeVPLB496 1 (2000)

STAR 200 GeV

PRL93 012301 (‘04)

O’H

ara

, e

t a

l, S

cie

nce

29

8 2

17

9 (

20

02

)




• hydro @ RHIC• misses scale (well-known)• impressive agreement on -dep


STAR PRL93 012301 (2004)Heinz&Kolb, PLB542 216 (2002)

“RHIC”




• hydro @ RHIC• misses scale (well-known)• impressive agreement on -dep

• prediction @ LHC• sign change in shape & oscillations



“RHIC”


“IPES” (LHC)

Sign flip in oscillations reflects transition to in-plane geometry(more flow, more time)


p+p: A clear reference system?


e+e- (and p+p, +p...) -- “similar” HBT radii

• high-quality/stats data sparse• diversity of methods

•corrections•coordinate systems

• jet axis in e+e-...•mixing...

• physics?

OPAL e+e- -> ZJuly 2007 CERN-PH-EP/2007-025


e+e- (and p+p, +p...) -- “similar” HBT radii

• high-quality/stats data sparse• diversity of methods

•corrections•coordinate systems

• jet axis in e+e-...•mixing...

• physics of “x-p” correlations in very small systems?•strings?• jets?•pythia + rescattering?•else?

i-th particle

Initial “disk” of radius r

talk by T. Humanic

L. Lonnblad - WPCF2007

Paic and SkowronskiJ. Phys. G31 1045 (2005)

see also Csorgo & Zajchep-ph/0412243 (ISMD04)

pT signal?


STAR preliminary

mT (GeV) mT (GeV)

Z. Chajecki WPCF05

Caution: femtoscopy in p+p @ STAR

• p+p and A+A measured in same

experiment with same method

• great opportunity to compare physics

• what causes pT-dependence in p+p?

• same cause as in A+A??


Surprising („puzzling”) scaling

HBT radii scale with pp

Scary coincidence or something deeper?

pp, dAu, CuCu - STAR preliminary

Ratio of (AuAu, CuCu, dAu) HBT radii by pp

• p+p and A+A measured in same

experiment with same method

• great opportunity to compare physics

• what causes pT-dependence in p+p?

• same cause as in A+A?

!! But !! significant issues with nontrivialinterplay non-femtoscopic correlations(restricted phasespace)- should be less of a problem at LHC- [see talk of T. Humanic]

A. Białasz (ISMD):I personally feel that its solution may provide new

insight into the hadronization process of QCD


5

as before (same pT dep etc)but scale by ~17%

as before (same pT dep etc)but scale by ~45%

NNUS: naive extrapolation HRM and AMPT

RL (50-100% 30%increase)[dynamics / chemistry / both ??]

RO,S • smaller increase (~30% 10%)• higher flow steeper pT dep

plats principaux

boissonsentrées

le menu des espérances au LHC

hydro

RL small increase (~30%)[huge flow rapid cooling short ]

RO,S : huge flow • larger increase (~60%)• steeper pT dep

shape inversion; oscillation sign flip

large tilt for central region?

p+p

pp

jet

jet

• signif pT dep• R increase w/ mult

• R increase w/ mult• other details??

• very large RO in high mult??

p+p “=“ A+A ???


+ - K+ K- K0S p p

+

-

- K+

K-

- - K0S

p

p

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

Does lock pattern break?

• extract phaseshifts (inversion of K-P paradigm)

• p+p in multiplicity classes [esp very low multiplicity]

• HBT relative to jets in p+p and A+A

• excitation function - (direct yield)


The end(...finally...)


Relative momentum resolution

• ITS+TPC tracks• 2 MeV/c (-> 100 fm, for scale only...)• del-qside small since azim. angle well-known• qout probes sagitta resolution

• heavier particles• less bending -> smaller sagitta -> worse resolution•but due to mT scaling, worse resolution is OK :-)



Track merging effects in the TPC• merging -> ~0.3 fm bias in HBT radius determination

for 8 fm source• less impt for smaller sources• less impt if Coulomb FSI included (?)• impact on imaging (non-Gaussian shapes) (?)

• merging correlated in qo-qs (can mimic “tilted source”)

• requiring separation in TPC helps remove effect, but convergence is slow



The ITS helps remove merging effects

• Ros = 0 as figure of merit• Cutting on ITS separation reduces

bias to ~0.1-0.2 fm


“similar triangles” : qmin/pT = separationMin/radius


Momentum resolution correction• “Triple-ratio” correction first (?) used by NA44• uses single-particle resolution (assumed

known) to smear “ideal” CF• rapid convergence


method of NA44/E895/STAR/...


HBT radii : “out versus in”

• good to ~15 fm



Event-by-event femtoscopy in Pb+PbALICE PPR (vol 2): J. Phys G. Part. Nucl. Phys. 32 1295 (2006)


reactionplane resolution

• At least as good as RHIC/STAR


Plot from

T. H

irano 2005

A menu of expectations for femtoscopy * 1.0 at LHC /ALICE

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