dan magestro the ohio state university for the star collaboration hbt relative to the reaction plane...

Dan MagestroThe Ohio State University

for the STAR Collaboration

HBT relative to the reaction plane at RHIC

Where we stand after Year-1

Motivation for HBT()

Centrality & kT dependence @ 200 GeV

Model discussion

Source geometry at freeze-out

2Transverse Dynamics workshop, March 2003 Dan Magestro

The role of HBT at a "transverse dynamics" workshop

• Single-particle pT spectra & v2 signal also determined by STE, but...

• Goal: quantify contributions to space-time evolution (STE) of system

Lifetime and duration of emission

Spatial extent of system

Collective flow at thermal freeze-out

Pairs of pions experience B-E correlations

Hanbury Brown–Twiss interferometry: characterize correlations

Width of correlation peak as q0 reflects "length of homogeneity"

(pair relative momentum)

• Bose-Einstein p correlations disentangle STE

static source: HBT radii ↔ true geometrical size of system

dynamic source: HBT radii ↔ flow reduces observed radii

pT dependence of HBT related to collective expansion


Review of RHIC Year 1 (s=130 GeV)

Hydrodynamics

Heinz & Kolb, hep-ph/0111075

momentum spectra

elliptic flow

Successfully reproduces p-space of source

Heinz & Kolb, hep-ph/0204061


Review of RHIC Year 1 (s=130 GeV)

"HBT Puzzle"

Hydrodynamics

Fails to predict spatial structure of source

Including hadronic rescattering makes it worse

Heinz & Kolb, hep-ph/0111075 STARPHENIX

hydro onlyhydro+hadronic rescatt

Soff, Bass, Dumitru


Why study HBT()?

• Standard HBT provides direct access to space-time (size) information about source, "HBT radii"

• Additionally, HBT() provides direct access to shape and orientation of source

• Source shape+size at freeze-out evolution, expansion rateHow much of initial spatial deformation still exists at freeze-out?

• Big question: What is the time scale of the collision?

later hadronic stage?b

x

beam into screen

Heinz & Kolb, Nucl.Phys. A702 (2002) 269-280

collective expansion of system


HBT() predictions from hydrodynamics

• Hydrodynamics: initial out-of-plane anisotropy may become in-plane

later hadronic stage?

in-plane-extended

out-of-plane-extended

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

kT dependence

Heinz & Kolb, Nucl.Phys. A702 (2002) 269-280


The HBT() experimental technique

2. Apply HBT formalism to extract "HBT radii" for each bin

reactionplaneb

x

beam into screen

1. Study (transverse) source at different angles by performing two-pion interferometry separately for bins w.r.t reaction plane

2

( , ) 1 i j ijq q RC q e

P=0°

p=90°

Rside (large)

Rside (small)

3. Oscillations of radii w.r.t. RP indicate if source is in-plane or out-of-plane extended

2 2 2 2 2 2 22( , ) 1 o o s s l l o s osq R q R q R q q RC q e 2

( , ) 1 i j ijq q RC q e


Watered-down HBT()

What we measure

HBT radii as a function of emission angle

reactionplane

What we expect to see:

2nd-order oscillations in HBT radii analogous to v2

Rside2

Why we're interested

The size and orientation of the source at freeze-out places tight constraints on expansion/evolution

What should be remembered

At finite kT, we don't measure the entire source size. We measure "regions of homogeneity" and relating this to the full source size requires a model dependence.

qoutqside

qlong


Blast-wave applied to HBT(), 130 GeV

• Minimum bias data (inclusive )

• Oscillations indicate out-of-plane extended source

• Blast-wave describes oscillations well

STAR preliminary

Ry=11.7 fm, s2=0.037, T=100 MeV, a=0.037, 0=0.9, askin=0.001

out side

out-side

long

P=0°

p=90°

Rside (large)

Rside (small)


Consistent picture of RHIC Year-1 (s=130 GeV)

Parametrization of freeze-out, works for v2, mT spectra, source geometry, and K- HBT

"Extended" blast wave1

1F. Retiere, nucl-ex/0111013

• Consistent set of parameters describes several observables

elliptic flow

HBT radiiK- correlations


Extending the HBT() systematics

130 GeV: minimum-bias analysis

Out-of-plane extended source, consistency with blast-wave

200 GeV: ~10x more statistics study systematics of HBT()

Centrality dependenceStudy source deformity at freeze-out in context of initial shape - geometry

kT dependenceStudy different scenarios of pair emission – geometry/dynamics

Warning: This is a very systematic analysis!


Corrections applied to data

Bowler/Sinyukov Coulomb correctionModifies fit function, leads to systematic increase in Rout

RP resolution correction1 (Heinz et al)Applies bin-by-bin corrections to Num's and Den's of correlation functions

Average lambda parameter for each centrality/kT binRemoves effects due to non-ideal behavior of fit function

+, - HBT parameters averagedImproves statistics; data consistent within errors

1 Heinz, Hummel, Lisa, Wiedemann, PRC 66 (2002) 044903


Effect of new Coulomb correction, "standard" HBT

))qqRexp(1(N)q(K)q(B

)q(A ji

2ij

coul

• RHIC analyses used “standard” Coulomb correction, used by previous experiments

• “apples-to-apples” extension of systematics

1f0 )1)q(K(f1)q(K coulcoul

• Effects of “diluting” CC (resonances, etc) explored & reported @ QM01

• Ro affected most

“Standard”Coulomb CCNo Coulomb CC

STAR, QM01; NPA698, 177c (2002)

• Y2 data: dilution effect vs pT, centrality• RO/RS ~ 10-15% increase when f = ≈ 0.5

f

1qqRexp(1)q(K1N)q(B

)q(Aji

2ijcoul

• More correct CC method of Bowler (’91) & Sinyukov (’98), used by CERES (’02)

• Similar effect on radii as dilution with f =

In “right” direction, but does not solve RO/RS problem

CERES Coll. NPA 714 (2002) 124


Centrality dependence of HBT()

12 -bin analysis (0.15 < kT < 0.65)

15° bins, 72 CF's total 12 bins × 3 centrality bins × 2 pion signs

Lines are fits to allowed oscillations

Oscillations exist in transverse radii for all bins

Amplitudes weakest for 0-10% (expected)

No higher-order oscillations observed

STAR preliminary

out, side, long go as cos(2)out-side goes as sin(2)


kT dependence of HBT()

10-30% events

STAR preliminary

To put this in perspective, the 130 GeV STAR HBT paper had 3 CF's per trend (centrality, pt)

4 -bin, 4 kT-bin analysis

96 simultaneous CF's 4 bins (45° wide) × 4 kT bins × 3 centrality bins × 2 pion signs

Oscillations exist in transverse radii for all kT bins


Data summary: Fourier coefficients

STAR preliminary

HBT() summary plot

• Data points are Fourier coefficients of oscillations

Ri,02 = Ri

2()/Nbins

Ri,22 = Ri

2()osc(2)/Nbins

i=o,s,l: osc = cosi=os: osc = sin

• All data consistent with out-of-plane extended sources

• Weak kT dependence


Hydro predictions of HBT()

RHIC (T0=340 MeV @ t0=0.6 fm)

• Initialize with central data, adjust geometry only

• 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)

Kolb & Heinz, Phys. Lett. B542 (2002) 216


Hydro predictions of HBT()

“LHC” (T0=2.0 GeV @ t0=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 @ t0=0.6 fm)




Kolb & Heinz, Phys. Lett. B542 (2002) 216


Comparison to Hydro

STAR preliminary

“LHC”/IPES (T0=2.0 GeV @ t0=0.1 fm)

• In-plane-extended source (!)

• HBT oscillations reflect competition between geometry, flow

• low KT: geometry

• high KT: flow sign flip

RHIC (T0=340 MeV @ t0=0.6 fm)





Model-independent determination of source orientation??

Issue: Are we being "tricked" by measurement? (Voloshin, Heinz, Kolb, ...)

reactionplane

reactionplane

vs.

Can we discriminate between these two scenarios in a model-independent way?(well, these drawings are already kind of a model-dependent picture...)

(a) (b)

High-kT – pairs emittedfrom small H.R.

As kT0, pions emitted from entire source

kT dependence• Pairs at different kT emitted from different homogeneity regions

• We observe no strong kT dependence of oscillation amplitude in transverse HBT radii finite kT measurements roughly representative of whole source...

• Case (b) requires some evolution of amplitude with kT

• Extrapolate toward kT=0 (risky, but...) to look at entire source...

• Model-independent determination of orientation of source!?


The Blast-wave parametrization

F. Retiere and M.A. Lisa, in preparation

• Blast-wave: Hydro-inspired parameterization of freeze-out

,S x K ( , )sr 2 2( ) / 2 /t te /cosh( ) K u TTm Y e momentum space

T, 0, a

x-spaceRx, Ry

timet, t7 parameters:

RY

RX

• Use Blast-wave to relate HBT() measurements to source shape & orientation


Characterizing freeze-out shape relative to initial anisotropy

0-10%

10-30%

30-70%

increases with b, indicates source is more out-of-plane extended

Glauber of initial geometry

Rx

Ry

Rx

Ry

HBT() of final geometry

y

x

R

R

Ry

0-10% 1.02 12 fm

10-30% 1.05 11 fm

30-70% 1.10 9.25 fm

other BW parameters kept fixedT=100 MeV, a=0.04, 0=0.9, askin=0.01

STAR preliminary


It didn't have to be this way...

Rx

Ry

Rx

Ry

Evolution scenarios – schematic only

1. Hydrodynamic source with strong flow, long lifetime

2. Explosive source with weak flow, very short lifetime

3. Rescattering/RQMD source with long lifetime

What would we have expected before doing the measurement?


Relevance to gluon saturation picture

1Kovchegov and Tuchin, Nucl. Phys. A 717 (2003) 249

• Kovchegov and Tuchin1 reproduced differential elliptic flow data using minijets in a gluon saturation model

• Consequence: reconstructed RP not related to real RP particle & v2 production is independent of geometry

Kovchegov and Tuchin, NPA 708 (2002) 413

• HBT(): Relates space-momentum correlations to reconstructed RP geometry does matter: saturation dead?

• Or, can minijets account for HBT() signal as well (at least qualitatively)?

• What can Color Glass / gluon saturation say about HBT?

reconstruted reaction planeusing v2

Transverse plane in K&T saturation scenario

true reaction plane

HBT() showssensitivity to reconstructed RP!


Conclusions

"Standard" HBT: Centrality and kT dependence

No significant change in radii from 130 GeV

Now: kT dependence of centrality dependence

Coulomb correction increases Rout ~10-15%

HBT puzzle persists...

HBT() @ 200 GeV: Centrality and kT dependence

Measurements consistent with out-of-plane extended sources

Short lifetime of source not enough time for flow to significantly affect shape

Hydrodynamics: reproduces amplitudes qualitatively with RHIC realistic source

Blast-wave: effective tool to extract source aspect ratio

Very little kT dependence of amplitudes model-independent determination of source orientation?

Does HBT() hurt the gluon saturation picture ??

dan magestro the ohio state university for the star collaboration hbt relative to the reaction plane...

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