dan magestro the ohio state university for the star collaboration
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HBT relative to the reaction plane at RHIC. Where we stand after Year-1 Motivation for HBT( ) Centrality & k T dependence @ 200 GeV Model discussion Source geometry at freeze-out. Dan Magestro The Ohio State University for the STAR Collaboration. - PowerPoint PPT PresentationTRANSCRIPT
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
3Transverse Dynamics workshop, March 2003 Dan Magestro
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
4Transverse Dynamics workshop, March 2003 Dan Magestro
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
5Transverse Dynamics workshop, March 2003 Dan Magestro
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
6Transverse Dynamics workshop, March 2003 Dan Magestro
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
7Transverse Dynamics workshop, March 2003 Dan Magestro
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
8Transverse Dynamics workshop, March 2003 Dan Magestro
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
9Transverse Dynamics workshop, March 2003 Dan Magestro
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)
10Transverse Dynamics workshop, March 2003 Dan Magestro
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
11Transverse Dynamics workshop, March 2003 Dan Magestro
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!
12Transverse Dynamics workshop, March 2003 Dan Magestro
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
13Transverse Dynamics workshop, March 2003 Dan Magestro
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
14Transverse Dynamics workshop, March 2003 Dan Magestro
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)
15Transverse Dynamics workshop, March 2003 Dan Magestro
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
16Transverse Dynamics workshop, March 2003 Dan Magestro
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
17Transverse Dynamics workshop, March 2003 Dan Magestro
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
18Transverse Dynamics workshop, March 2003 Dan Magestro
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)
• Out-of-plane-extended source (but flips with hadronic afterburner)
• flow & geometry work together to produce HBT oscillations
• oscillations stable with KT
Kolb & Heinz, Phys. Lett. B542 (2002) 216
19Transverse Dynamics workshop, March 2003 Dan Magestro
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)
• Out-of-plane-extended source (but flips with hadronic afterburner)
• flow & geometry work together to produce HBT oscillations
• oscillations stable with KT
20Transverse Dynamics workshop, March 2003 Dan Magestro
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!?
21Transverse Dynamics workshop, March 2003 Dan Magestro
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
22Transverse Dynamics workshop, March 2003 Dan Magestro
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
23Transverse Dynamics workshop, March 2003 Dan Magestro
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?
24Transverse Dynamics workshop, March 2003 Dan Magestro
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!
25Transverse Dynamics workshop, March 2003 Dan Magestro
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 ??