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Sergey Panitkin
Current Status of the RHIC HBT Puzzle
Sergey PanitkinBrookhaven National Lab
La Thuile, March 18, 2005
Sergey Panitkin
Who cares about the soft sector?
99.5%
• Well-justified excitement about high-pT physics
• But recall that we want to create/study a new type of matter (= bulk system)
• large-scale (soft?) deconfinement• Collective properties (T,p, flow?)
• Jets/ect are probes of this system
• Crucial to understand bulk properties and dynamics in their own right
Sergey Panitkin
Collective behavior at RHIC
P. Kolb, J. Sollfrank, U. Heinz
Heinz & Kolb, hep-th/0204061
• Hydrodynamics seems to reproduce p-space aspects (spectra and elliptical flow) of particle emission up to pT~2GeV/c
Bulk system?!Note: Hydro provides complete space-time evolution. Can be tested!
Sergey Panitkin
Two-particle Correlations
Single particle spectrum is sensitive to momentum distribution only
Relative momentum distribution of particle pairs is sensitive to space-time information
Intensity interferometry, HBT technique, etc….
),(4 pp
xSdxddNE
),(|),(|)/)(/(
/)( 2
2111
2122 qrqrr
pppp
q SdddNddN
dddNC
Source functionFSI
Sergey Panitkin
Two particle Interferometry: Idealized case
y
X
1
2
Source
24
2xiq4
21)K,x(Sxd
e)K,x(Sxd1)p,p(C
21 ppq 2121 ppK
emission function
For non-interacting identical bosons:
C (Q
inv)
Qinv (GeV/c)
1
2
0.05 0.10
Width ~ 1/R
Sergey Panitkin
Correlation functions for different colliding systems
C2(
Qin
v)
Qinv (GeV/c)
STAR preliminary p+pR ~ 1 fm
d+AuR ~ 2 fm
Au+AuR ~ 6 fm
Correlations have more informationOne can use more sophisticated analysis to extract it
Sergey Panitkin
beam direction
p1 p2
Q T
Q
Q L
beam direction
p2p1
Q T
Q S
Q O
“Standard” Pratt-Bertsch coordinate system
)T2
PT1
P(2
1T
K
2long
2long
2side
2side
2out
2out)(1),(
RqRqRqekkqC
Sergey Panitkin
HBT for Gaussian sources
Kt~x~KR
Kx~KR
Kt~x~KR
2llong
2l
2side
2s
2out
2o
xxx~
)K,x(Sxd
)x(f)K,x(Sxdf
4
4
Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentum KT
qSide : qLong & qOut
222222
1),,( llssoo RqRqRqlso eqqqC
Radii are related to source variances:
221
21
ppk
ppq
In Longitudinally Co-Moving System (LCMS) l =0
Sensitive to emission time
Sensitive to transverse extent
Sensitive to longitudinal extent
Sergey Panitkin
In Search of the QGP. Naïve expectations
QGP has more degrees of freedom than pion gas
Entropy should be conservedduring fireball evolution
Hence: Look in hadronic phasefor signs of: Large size, Large lifetime, Expansion……
Sergey Panitkin
In Search of the QGP. Expectations.
“Energy density”
•One step further:•Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ 2->4 @ Kt = 350 MeV.•Looking for a “soft spot”
Sergey Panitkin
Excitation function of the HBT parameters
• ~10% Central AuAu(PbPb) events
• y ~ 0
• kT 0.17 GeV/c
no significant rise in spatio-temporal size of the emitting source at RHIC
Ro/Rs ~ 1
Some rise in Rlong
Note ~100 GeV gap betweenSPS and RHIC
Sergey Panitkin
RHIC Energy Scan
•Measurements at 200, 130, 62 GeV
•No significant change with energy
•Ro/Rs ~1
PHOBOS nucl-ex/0409001
Where are signs of phase transition?!
Is HBT sensitive to geometry at all?!
Sergey Panitkin
More Experimental Systematics
STAR PRL 93:12301 (2004)PHENIX nucl-ex/0401003
Clear sensitivity to source geometry !
b≠0
Centrality dependence asHBT
Sergey Panitkin
Source expansion at RHIC
initi
al =
final
22
22
xy
xy
RR
RR
Rx
Ry
STAR preliminary
STAR Collaboration, nucl-ex/0312009
Expansion at low Pt Change in eccentricity of the source
Sergey Panitkin
Model Comparison (the puzzle)
Subset of models shown
Broad range of physics scenarios explored
Good description of p-space
Poor description of HBT data
the puzzle
Does Rout/Rside of unity imply no long-lived mixed phase?
Sergey Panitkin
x-tx-t Correlation of Source Function Correlation of Source Function
Why hydro doesn’t work? positive!
x
t
Negative x-t correlation
Positive? Negative?
Typical source functionfrom hydro with Bjorken flow
x
t
Positive x-t correlation
Hubble like flow?Buda-Lund, AMPT
Rout~Rside may require positive x-t corr.
Sergey Panitkin
BudaLund fits to 130 GeV data
PRC54 (1996) 1390, NPA 590 (1995) 465
Parameterization, not a model !
Sergey Panitkin
Conclusions
Rich set of experimental HBT results exists at RHIC Large number of models has been developed to explain RHIC physics Good description of momentum space observables Evidence that matter at RHIC exhibits collective bulk properties Most models still can not reproduce simultaneously experimental
observables at low Pt: v2, spectra, correlations, dN/dy, etc We are gaining better understanding of model failures Bjorken longitudinal boost-invariance assumption seems to be one of
the sources of discrepancies (at least for Hydrodynamical models) More detailed correlation measurements will be available soon: non-
identical correlations, HBT Pt>1 GeV/c, Kaons, protons, etc Stay tuned!
Sergey Panitkin
The END
Sergey Panitkin
Back Up slides
Sergey Panitkin
Does HBT in rhic make sense?
YES… Size [R(Npart
1/3)] Shape [R( )] Dynamic structure [R(mT)]
… and NO? Model disagreement
[transport]? Too-short timescales [BW]
? Inconsistent dynamical picture
? No large rise in RO, RL [general]
Sergey Panitkin
BL-H sourceparameters
BudaLundv2.0
BudaLundv2.0 Hubble+T
T0 [MeV] 182 19 160 15<ut> 1.16 0.09 fixed RG /0
RG [fm] 9.2 0.6 10.0 0.5
0 [fm/c] 7.3 0.6 7.9 0.4 [fm/c] 0.0 0.5 0.2 0.4 2.36 0.04 2.38 0.05Tsurf [MeV] 92 5 89 4Teva [MeV] 110 14 114 15
0- [MeV] 78 15 76 10
0K- [MeV] 134 30 148 16
0p- [MeV] 382 59 411 23
0+ [MeV] 65 12 66 8
0K+ [MeV] 162 30 173 15
0p [MeV] 446 58 467 22
/NDF 213./180 =1.19 214/181 =1.18
CL 4.5 % 4.5 %
Buda-Lund fits to 130 GeV data
Sergey Panitkin
Fourier coefficients of HBT() oscillations
0th-order FC: centrality & kT dependence mirrors -integrated analyses; quantitatively consistent
Relative amplitudes increase from central to peripheral collisions
means relative amplitudes
STAR Collaboration, nucl-ex/0312009
• Freeze-out eccentricity can be estimated from relative amplitudes
• Blast-wave: rel. amplitudes sensitive to spatial anisotropy, depend weakly on collective flowRetiere and Lisa, nucl-th/0312024
• Freeze-out eccentricity can be estimated from relative amplitudes
• Blast-wave: rel. amplitudes sensitive to spatial anisotropy, depend weakly on collective flowRetiere and Lisa, nucl-th/0312024
20,
22,
20,
22,
20,
22,
22
22
222s
o
s
os
s
s
xy
xy
R
R
R
R
R
R
RR
RR
no temporal component
Sergey Panitkin
Comparison to PHENIXAuAu 200 GeV 30% Centrality
Sergey Panitkin
Elliptic geometry leads to oscillations of the radii
– For example Rside
b
Rsi
de2
(fm
2 )
Out-of-plane In-planeCircular
(degree)out-of-planeextended source
p=0°
p=90°
Rside (large)Reactionplane
Rside (small)
Naïve view with no flow
HBT with respect to reaction plane
Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)
Sergey Panitkin
qout
qside
qlong
Hanbury Brown-Twiss interferometry
Rsi
de
R long
Rout
x1
x2
12 ppq
p1
p2
q
12 pp2
1k
Two-particle interferometry: p-space separation space-time separation
HBT: Quantum interference between identical particles
pairsevent mixed
pairsevent real
)(P)(P
),(P),(
21
2121
pp
ppppC
2long
2long
2side
2side
2out
2out)(1),(
RqRqRqekkqC
q (GeV/c)q (GeV/c)
C (
q)C
(q)
11
22R
1~
– Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for
Gaussian model (3-d):