Download - Dan Magestro The Ohio State University for the STAR Collaboration HBT relative to the reaction plane at RHIC Where we stand after Year-1 Motivation for

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 ??

Download - Dan Magestro The Ohio State University for the STAR Collaboration HBT relative to the reaction plane at RHIC Where we stand after Year-1 Motivation for

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