particle correlations at star jan pluta heavy ion reactions group (hirg), faculty of physics, warsaw...
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PParticle correlationsarticle correlations at STARat STAR
Jan Pluta
Heavy Ion Reactions Group (HIRG),
Faculty of Physics,
Warsaw University of Technology
Some results from the STAR HBT
group, presented recently by:
Z.Chajecki, A.Kisiel, M.Lisa,
M.Lopez-Noriega, S.Panitkin,
F.Retiere, P.Szarwas.
3-rd Budapest Winter School on Heavy Ion Physics, 10 XII 2003
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Outline:
•The STAR experiment
•RHIC HBT Puzzle
•General analysis
•asHBT
•Two K0-short correlations
•p-Au, d-Au data
•Nonidentical particles - emission asymmetry
•Plans for future
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Relativistic Heavy Ion Collider (RHIC)
2:00 o’clock
4:00 o’clock6:00 o’clock
8:00 o’clock
10:00 o’clock
STARPHENIX RHIC
AGS
LINACBOOSTER
TANDEMS
9 GeV/uQ = +79
1 MeV/uQ = +32
HEP/NP
g-2U-line
BAF (NASA)
PHOBOS12:00 o’clock BRAHM
S
Beam energy up to 100 GeV/A (250 GeV for p) Two independent rings (asymmetric beam collisions are
possible) Beam species: from p to Au Six interaction points Four experiments: STAR, PHENIX, PHOBOS and BRAHMS
=3.8 km1740 superconducting magnets
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Solenoidal Tracker At RHIC
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STAR Detector – side viewSTAR Detector – side view
and STAR Collaboration – face view
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STAR Collaboration• 500 Collaborators
including– ~65 graduate students– ~60 postdocs
• 12 countries• 49 institutions• Spokesperson:
John Harris 1991 - 2002
Tim Hallman 2002 - now
USA, Brazil, China, Croatia Czech Republich, England, France, Germany, India, Netherlands, Poland, Rusia
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HBT+FSI
Space-time
sizes anddynamics
Correlation function
Momenta andmomentum difference
The idea:
Quantum statistics and Final-State Interaction
Particle correlations
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STAR Event 2
Central Event: AuAu 200GeV/A
Real-time track reconstruction Pictures from Level 3 Trigger, online display.
Typically 1000 to 2000 tracks per event into the
TPC
4m
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Event and Particle SelectionAu+Au Collisions at Sqrt(SNN)=200GeV
• Particle identification via specific ionization (dE/dx)electron band removed by cuts
• Optimum performance for HBT: 0.150 < pT (GeV/c) < 0.550
for K0s:
0.100 < pT (GeV/c) < 3.500
• Centrality selection based on number of charged hadrons.
three different centralities
• Midrapidity-0.5 < y < 0.5
STAR PRELIMINARY
N ch
STAR PRELIMINARY
Minbias trigger
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Two-particle kinematics
Main
(approximative)
relations:
Qout <--> Pt
Qside <-->
Qlong <-->
KT <--> Pt
Some base definitions - to be used for results presentation
LCMS: (P1+P2)z=0
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HBT Excitation Function
Comparison with lower energies for
~ 10% most central events at
midrapidity
kT ~ 0.17 GeV/c
No significant increase in radii with energy
RO/RS ~ 1
Gap in energy that needs to be closed
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RHIC HBT PuzzleMost “reasonable” models still do not
reproduce RHIC sqrt(SNN) = 130GeV
HBT radii
“Blast wave” parameterization (Sollfrank
model) can approximately describe data
…but emission duration must be small
= 0.6 (radial flow)
• T = 110 MeV
• R = 13.5 1fm (hard-sphere)
emission= 1.5 1 fm/c (Gaussian)
fromspectra, v2
√SNN = 130GeVPHENIX PRL 88 192302 (2002)
STAR 130 GeV
PHENIX 130 GeV
+
-
Hydro + RQMD
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Statistical errors only!!
raw
Coulombcorrected
q* (GeV/c)
3Dimensional Pion HBT
Pratt-Bertsch Parameterization
LCMS frame: (p1+p2)z=0
Central Events pT = 0.15-0.25 GeV/c
Coulomb correction→ spherical Gaussian source of 5fm
momentum resolution corrected(~1% effect at 200GeV, due to higher B-field)
)( 222222
1),,( LLSSOO RqRqRq
LSOeqqqC
Rout (fm) Rside (fm) Rlong (fm)
0.66 ± 0.01 6.41 ± 0.14 6.03 ± 0.09 6.65 ± 0.11
STAR PRELIMINARY
Sqrt(SNN) = 200 GeV– –
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Centrality and mT dependence at 200 GeV
RL varies similar to RO, RS with centrality
HBT radii decrease with mT (flow)
Roughly parallel mT dependence for different centralities
RO/RS ~ 1 (short emission time)
Central
Midcentral
Peripheral
200GeV
STAR PRELIMINARY
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Longitudinal radius:at 200GeV identical to 130 GeV
(fit to STAR Y2 data only)
STAR PRELIMINARY
Central
Midcentral
Peripheral
PHENIX Central
200GeV - 130 GeV
Comparison: 200 to 130 GeV. Longitudinal radius
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Evolution timescale from RL
(fit to STAR Y2 data only)
Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow)
T
KfoL m
TtR
Assuming TK=110 MeV(from spectra at 130 GeV)
fm/c 6.7t
fm/c 10t
periphfo
centralfo
Makhlin and Sinyukov,
Z. Phys. C 39 (1988) 69
STAR PRELIMINARY
Central
Midcentral
Peripheral
PHENIX Central
200GeV - 130 GeV
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Comparison: 200 to 130 GeV. Transverse radii
*
Central
Midcentral
Peripheral
PHENIX Central
200GeV - 130 GeV
Higher B-field higher pT
Transverse radii:
• similar but not identical• low-pT RO, RS larger at 200 GeV• steeper falloff in mT
(PHENIX 130GeV)• Ro falls steeper with mT
STAR PRELIMINARY
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Azimuthally sensitive HBT (asHBT)
• sensitive to interplay b/t anisotropic geometry & dynamics/evolution
• “broken symmetry” for b0 => more detailed, important physics information
• another handle on dynamical timescales – likely impt in HBT puzzle
P. Kolb and U. Heinz, hep-ph/0204061
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HBT respect Reaction Plane
out
p
b
K
side
x
y
2ijji Rqq
e1),q(C
Lines: projections of 3D Gaussian fit
1D projections, =45° √SNN = 130GeV
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HBT(φ) Results – 130 GeV
Star preliminary
Minbias events @130GeV
Bolstered statistics by summing results of p- and p+ analyses
Blast-wave calculation (lines) indicates out-of-plane extended source
Data corrected for both event plane resolution and merging systematic
T=100 MeV 0aR=11.7 fm,
=2.2 fm/c
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RY
RX
A model of the freezeout - BlastWave
BW: hydro-inspired parameterization of freezeout• longitudinal direction
• infinite extent geometrically• boost-invariant longitudinal flow
• Momentum space• temperature T• transverse rapidity boost ~ r
)2cos(~),( 0 bas rr
• coordinate space• transverse extents RX, RY
00 r~R
r)r(
• freezeout in proper time • evolution duration 0
• emission duration
2
20
2exp~
ddN
00
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RY
RX
A model of the freezeout- BlastWaveBW: hydro-inspired parameterization of freezeout• Longitudinal direction
• infinite extent geometrically• boost-invariant longitudinal flow
• Momentum space• temperature T• transverse rapidity boost ~ r
)2cos(~),( 0 bas rr
• Coordinate space• transverse extents RX, RY
00 r~R
r)r(
• freezeout in proper time • evolution duration 0
• emission duration
2
20
2exp~
ddN
7 parameters describing freezeout
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BlastWave fits to published RHIC data
• reasonable centrality evolution
• OOP extended source in non-central collisions
central midcentral peripheral
74.3 / 68153.7 / 9280.5 / 1012 / ndf
0.8 1.90.8 3.20.0 1.4 (fm/c)
6.5 0.87.4 1.28.9 0.30 (fm/c)
10.1 0.411.8 0.612.8 0.3RY (fm)
8.0 0.410.2 0.512.9 0.3RX (fm)
0.04 0.010.05 0.010.06 0.01a
0.81 0.020.87 0.020.88 0.010
95 4106 3108 3T (MeV)
PeripheralMidcentralCentral
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Estimate of initial vs F.O. source shape
2x
2y
2x
2y
RR
RR
20,S
22,S
FO R
R2
• estimate INIT from Glauber
• from asHBT:
FO =
INIT
FO < INIT → dynamic expansion
FO > 1 → source always OOP-extended
• constraint on evolution time
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asHBT at 200 GeV in STAR – R() vs centrality
12 (!) -bins b/t 0-180 (kT-integrated)
• 72 independent CF’s
• clear oscillations observed in
transverse radii of symmetry-
allowed* type
• Ro2, Rs
2, Rl2 ~ cos(2)
• Ros2 ~ sin(2)
• centrality dependence reasonable
• oscillation amps higher than 2nd-
order ~ 0→
(*) Heinz, Hummel, MAL, Wiedemann, Phys. Rev. C66 044903 (2002)
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Pion correlation in d – Au : data selection
p-Au selection
1D correlation function
3D correlation function
d-Au vs p-Au
KT dependence
Centrality dependence
Pion Correlations d-Au and p-AuPion Correlations d-Au and p-Au
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p-Au selection:p-Au selection:
Using information from ZDC-d STAR can separate events with neutron spectator from deuteron
ZDC-dAu d
ZDC-Au
FTPC E -Au
All trigger events
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1D Correlation Function:1D Correlation Function:
Gaussian fit:
➢ CF is very wide (rel Au-Au)➢ Coulomb/merging less important➢ CF looks reasonable➢ 1D Gaussian fit is not good➢
needed more deeply study of fit
method
STAR preliminarytheoretical CF: R
inv=6 fm, = 0.5
d*-Au : d-Au without p-Au
collision 1.89 +- 0.01 0.364 +- 0.003 4672 / 33
d – Au 1.85 +- 0.01 0.362 +- 0.003 5359 / 33
Rinv [fm] NDF
d* – Au
only statistical error included !
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3D Correlation Function:3D Correlation Function:
Gaussian parametrization is not perfect but HBT radii characterize the width of CF
cut on the others Q's
components < 30 MeV/c
3D Gaussian fit:
STAR preliminary
d – Au p – Au
1.58 +- 0.02 1.21 +- 0.03
1.51 +- 0.01 1.21 +- 0.02
1.71 +- 0.02 1.67 +- 0.05
0.354 +- 0.003 0.372 +- 0.008
Rout
Rside
Rlong
Fit results:
Rout
, Rside
sensitive to the number of participants
[GeV/c]
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KKTT dependence: dependence:
p – Au d – Au
● clear KT dependence
●Rout
and Rside
- sensitive to the number of participants●R
long – the same K
T
dependence for dAu and pAu
STAR preliminary
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KKTT dependence: d-Au & Au-Au divided by p-p dependence: d-Au & Au-Au divided by p-p
● the same trend of KT
dependence for d-Au
and Au-Au as for p-p ● HBT radii are scaled by constant factors
STAR preliminary
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for different collisions
MMTT dependence of R dependence of Rlonglong: :
STAR preliminary
Rlong
= const (mT)-
p-p d-Au Au-Au Au-Au peripheral midcentral
STAR preliminary
mTk
T2 + mass
Sinyukov fit:
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Centrality definition in d-Au:Centrality definition in d-Au:
centrality bin FTPC multiplicity percent of events
1 [0 , 9] 100 – 40
2 [10 , 16] 40 – 20
3 [17 , 99] 20 – 0
FTPC-Au: charged primary particle multiplicity in -3.8<<-2.8
ZDC-dAu d
ZDC-Au
FTPC E -Au
321
most peripheral
most central
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Centrality dependence:Centrality dependence:
● clear centrality dependence
● similar to AuAu
● connection to geometry
p – Au d – Au
centrality
minbias
STAR preliminary
1 2 3
4.3 +- 0.1 10.4 +- 0.4 16.3 +- 0.7<Npart> [*]
<Nch
> TPC . 7.9 . . 12.1 . . 17.1 .
<Nch
> FTPC E . 5.2 . . 12.8 . . 24.3 .
[*] - Glauber calculations (Mike Miller)
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K0sK0
s Correlations
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mt scaling violation?
Next RHIC HBT puzzle ?
inv
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The asymmetry analysis
Catching up•Interaction time larger•Stronger correlation
Moving away•Interaction time smaller•Weaker correlation
“Double” ratio•Sensitive to the space-time asymmetry in the emission Kinematics selection
on any variablee.g. kOut, kSide, cos(v,k) R.Lednicky, V. L.Lyuboshitz,
B.Erazmus, D.Nouais,Phys.Lett. B373 (1996) 30.
Non-identical particle correlations:
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Double ratio definitions
p1
p1
p2
p2
2k* = p1 – p
2 P = p1 + p
2
kside
< 0
kside
> 0
kout
> 0
kout
> 0
kksideside signselectionarbitrary
kkoutout signselection determined by the directionof the pair momentum P
Correlationfunctions
Double ratios
kklong long is the z componentof the momentumof first particle in LCMS
2k* [GeV/c]
simulation
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What to expect from double ratios
• Initial separation in Pair Rest Frame (measured) can come from time shift and/or space shift in Source Frame (what we want to obtain)
• We are directly sensitive to time shift, the space shift arises from radial flow – possibility of a new radial flow measurement
r
T
F
x
yobservedtransversevelocity
thermal velocity
Flow velocity Out direction
Side direction
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What do we probe?
Source ofparticle 1
Source ofparticle 2
Boost to pair rest frame
• Mean shift (<r*>) seen in double ratio
• Sigma (r*) seen in height of CF
r* =pairr–pairt
Separation between source 1 and 2 in pair rest frame
r
r (fm) r* (fm)
<r*>
r*
Separation due to space and/or time
shift
t
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Correlation functions and ratios
Good agreement for like-sign and unlike-sign pairs points to similar emission process for K+ and K- Out
Side
Long
CF
Clear sign of emission asymmetry
Two other ratios done as a double check – expectedto be flat
Preliminary
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STARpreliminary
Results for Pion-Proton 130 AGeV
• Similar preliminary analysis done for pion-proton
• We observe Lambda peaks at k*~m
inv of Λ
• Good agreement for identical and non-identical charge combinations
Λ peaks
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Preliminary results for Kaon-Proton
• Using data from Year2 (200 AGeV) – sufficient statistics
• No corrections for momentum resolution done
• No error estimation yet – fit indicates theoretical expectations
K+ pK- anti-pBest Fit
STARpreliminary
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Modeling the emission asymmetry
• Need models producing strong transverse radial flow:– Blast-wave as a
baseline– RQMD– UrQMD– T. Humanic's
rescattering model
• What do we measure and how to compare it to the models?
• Is our fitting method working? And if yes, what does it tell us?
• Need to disentangle flow and time shift
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Understanding modelsBlast wave = Flow baseline
• Blast wave– Parameterizes source size
(source radius) radial flow (average flow rapidity) and momentum distribution (temperature):
– No time shift– Only spatial shift due to flow
– Infinitely long cyllinder (neglects long contribution)
R
t
RsideRout
Kt = pair Pt
Parameterizationof the final state
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Blast wave: how does the flow workBlast wave: how does the flow work
Pionp
t = 0.15 GeV/c
t = 0.73
Kaonp
t = 0.5 GeV/c
t = 0.71
Protonp
t = 1. GeV/c
t = 0.73
Average emission points
Spatial shifts (r) Particle momentum
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Fitting and quantitative comparisons
• Fits assume gaussian source in PRF
• r*out
distributions have non-
gaussian tails• Use the same fitting
procedure for models and data - correlation functions constructed with “Lednicky's weights”
Example of r*out
distribution from RQMD
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Comparing models to data
• Rescattering models and blast-wave are consistent with data
• Blast wave parameters constrained by STAR measurements
• In models flow is required to reproduce the data
• More points in βt needed to map and discriminate the flow profile – needs
STAR upgrades in PID capability (TOF barrel)
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STAR HBT Matrix (circa 2003)
+ - + - 0 p p ++ +
0 -
+
-
Sergei's HBT matrix 0
Y1 p
Y1 ? p
Y2
“traditional”HBT axis
Analysisin progress
published
3 Correlations (accepted PRL)asHBTPhase space densityCorrelations with CascadesdAu, ppCascades
submittedNot shown:
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What have we learned so far?
• RHIC HBT puzzle– Break down of theoretical description of correlations at RHIC– Indication of short source lifetime and freeze-out duration at RHIC– Short lived hadronic phase?
• Out of plane extended pion source in non-central collisions– Also points to short emission times
• Weak energy dependence of the HBT radii– Where is the phase transition?
• Large pion phase space densities (non-universal)– Small entropy per pion?
• Chaotic pion source from 3p correlations– No multiparticle effects above Pt~200 MeV/c
• Source asymmetries from non-identical correlations– Consistent with collective flow and short time scales
• Only systematics measurements may provide answers!
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What will affect STAR HBT analysis?
• RHIC upgrades progress• STAR upgrades• Various other measurements (e.g. spectra,
high Pt,
strangeness, flow, etc)• New theoretical ideas
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Consequences for STAR HBT• Large statistics AuAu datasets • Plans for 2004: 14 weeks of AuAu “physics” running:
– ~30M central, ~50M peripheral events• What can be done? Many analysis which were statistics limited!
– Rare particle correlations W, X,L, etc (identical, non-identical)• Early freeze-out, sequence of emission, flow, FSI, etc
– Correlations relative to reaction plane• Kaons• Non-identical
– Baryon correlations: ppbar, LLbar, pL, etc– Coalescence, light nuclei and anti-nuclei
• Large statistics pp (~100M events) datasets @200, 500 GeV– STAR HBT matrix (e.g. non identical correlations)– HBT in Jets?– spin dependent HBT? (with polarized beams)
• Different energies • Different beams
Add dependencies on centrality, Kt, reaction planeEvent by Event HBT
New analyses ideas (S.Pratt, imaging, etc)
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Consequences for STAR HBT
• Better particle identification• Extension of HBT systematics to higher Kt: 1-3
GeV/c• Region of transition from Hydro to pQCD• What is space-time picture in this region?
– Correlations of identical particles– Scan in Pt for Non-identical correlations
• Sensitivity to flow profile, model details– asHBT
• Higher efficiency of hyperons reconstruction– ~x10 for W compare to TPC alone– High statistics correlations with hyperons
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Summary
• RHIC and STAR future seems to be certain for next 5-10 years
• Upgrade path is visible• The number of available datasets and possible
analysis topics will be rapidly increasing• Data volumes will be unprecedented (at least for
us)– Can we do analysis in a reasonable time?
• Analyses will be “moving” to rare particles• Shall we continue with systematic approach?
– Probably yes• If new results or theoretical predictions will suggest
promising measurement - we will concentrate on it