dan magestro the ohio state university for the star collaboration hbt relative to the reaction plane...
TRANSCRIPT
![Page 1: 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](https://reader035.vdocument.in/reader035/viewer/2022081603/56649f395503460f94c56581/html5/thumbnails/1.jpg)
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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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!
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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
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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
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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)
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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
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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
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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
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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
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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
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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!?
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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
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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
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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?
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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!
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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 ??