First Results on Two-Particle Correlations Determined by PHENIX
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Transcript of First Results on Two-Particle Correlations Determined by PHENIX
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Stephen C. Johnson forthe PHENIX Collaboration
First Results on Two-Particle Correlations Determined by PHENIX
Stephen C. Johnson
Lawrence Livermore National Lab
for the PHENIX Collaboration
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Stephen C. Johnson forthe PHENIX Collaboration
Why study particle correlations?(Preaching to the choir)
• Measures the relative spatial-temporal separation at the point of last interaction – Sensitive to relative
separation in phase space of pairs at freeze-out
)(r
)(~1)(
)(2 q
qB
qAC
Assuming a chaotic source with no dynamical correlations and no final state interactions the resulting correlation function is rather straight-forward:
C2
1/R
q
p1
p2
p2
p1
q
2
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Stephen C. Johnson forthe PHENIX Collaboration
But Beware!!
• “C2 depends on more variables than you can think of.”– Anonymous HBT expert
• In particular– Dynamical correlations
– Lorentz kinematics
**This first figure unabashedly stolen
from M. Lisa
Be careful with assumptions of symmetric and static sources!!
flow
RO
RS
**
RS2+22=RO
2
e.g.
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Stephen C. Johnson forthe PHENIX Collaboration
Agenda
• First PHENIX HBT results from Run 1.
• Proof of principle – capability of PHENIX to perform these measurements– PID capabilities and analysis– 1D correlations– Bertsch-Pratt 3D fit to ROSL
– Confirm dependencies of R on kt
• Comparisons and Conclusions
• A glance at future capabilities.
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Stephen C. Johnson forthe PHENIX Collaboration
Particle identification
Tracking with Drift Chamber/Pad Chambers
Time of flight with TOF & Beam-Beam Counter
“Particle identification capability of the PHENIX experiment”
H. Hamagaki
• For this analysis: = • 2 within peak
• 3 away from K peak
• 180<p< 2000 MeV/c
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Stephen C. Johnson forthe PHENIX Collaboration
Pair Acceptance• Acceptance about time-of-
flight wall restricts correlation measurement to ypair<.3
• PHENIX excellent PID allows pair reconstruction to very high kt– => larger statistics of year-2
will allow high kt 3D measurements
All pairsLow q pairs
Raw
Cou
nts
(A.U
.)
MeV
ppppk yyxxt
350
)()(2
1 221
221
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Stephen C. Johnson forthe PHENIX Collaboration
q Acceptance
~qTside
~qout qlong
• Finite acceptance in y and => finite qTside and qlong reach.
• Excellent particle identification to large p => large qTout bite.
kt
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Stephen C. Johnson forthe PHENIX Collaboration
MeVq
MeVq
Tout
Tside
100
100
MeVq
MeVq
Tside
long
100
100
MeVq
MeVq
Tout
long
100
100
q acceptance
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Stephen C. Johnson forthe PHENIX Collaboration
Centrality• All data presented today
are for ‘minimum bias collisions’ (i.e. only with trigger on zvtx)
• However: finite detector + minimum bias sample + pairs requirement– => bias towards central
collisions in min bias sample
• Truly a central event sample
%17
%15
events
pairs
centrality
centrality
PHENIX Preliminary
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Stephen C. Johnson forthe PHENIX Collaboration
Qinv distributions
Qinv (MeV/c)
C2
• Full coulomb correction…– Analytic coulomb
correction assumes R(Qinv) source
– Resulting radii independent of RQinv input within ~10%
• Qinv => measurement of relative separation of the pair in the pair rest frame– Acceptance dependent!!
PHENIX Preliminary
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Stephen C. Johnson forthe PHENIX Collaboration
Rl = 4.0 1.2RTside = 7.9 1.1RTout = 6.23 .54 = .493 .050
Rl = 6.7 .9RTside = 5.8 1.5RTout = 5.49 .54 = .493 .061
Bertsch-Pratt Fit Results
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Stephen C. Johnson forthe PHENIX Collaboration
1D correlations
– Full coulomb correction
– q =>Measure of relative separation of pair in the rest frame of the collision.
q (MeV/c)
C2
R=6.5 .9=.38 .08
R=4.5 .6=.28 .05
R=4.5 .5=.34 .06
R=6.0 .8=.38 .08
R=4.8 .5=.48 .08
R=3.7 .6=.37 .09
PHENIX Preliminary
MeVkt 195 MeVkt 524MeVkt 307
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Stephen C. Johnson forthe PHENIX Collaboration
As a function of kt
• kt dependence is well behaved
• Measured relative separation of pions from source expected to decrease versus kt possibly due to collective behavior of source or resonance contributions.
PHENIX Preliminary
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Stephen C. Johnson forthe PHENIX Collaboration
Comparisons• No indication of large
volumes
• Comparable results to SPS and preliminary STAR with similar <kt>/centrality
– Not exactly the same, so be careful…
• Perhaps indicative of same effective freeze-out due to convolution of– larger source and
– stronger dynamical correlations / high flow velocities / resonances(?)
Star Preliminary (M. Lisa)NA44NA49E866E895PHENIX Preliminaryroot-s
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Stephen C. Johnson forthe PHENIX Collaboration
Conclusions*• First measured correlation function from PHENIX at
RHIC including most Run 1 dataset:
– 1D correlation looks well behaved => used to determine coulomb correction.
– 3D correlation comparable to SPS published and STAR preliminary results when comparing similar kt bins
– Dependencies of Rl and Rs on beam energy are gradual and well behaved.
– No indication of long lived source in correlation function• But be careful what you conclude from that…
• First proof-of-principle methodology -- looking forward to increased statistics and systematic studies…
* Don’t leave yet, I still have 3 more slides…
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Stephen C. Johnson forthe PHENIX Collaboration
For the future...• This year
– Complete systematic studies of correlations
– h-h- -p, -K (1D)
– with EMCAL:• , KK, pp (1D)
• Next year– 100x statistics =>
• vs centrality and kt
• pp, KK
– with EMCAL• anti-neutron, (?)
• In general– Are there other methods we can use to extract info from
correlations? ==>
Coherent interpretation of source size
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Stephen C. Johnson forthe PHENIX Collaboration
Other methods
– Explicit inversion of correlation function to deduce relative separation of pairs at freeze-out.
– How sensitive is this method to the source?
• Can we learn more than just the RMS?
• Extract multi-D source parameters?
• Systematic studies underway.
Brown and Danielewicz nucl-th/0010108
Figure and studies by Mike Heffner
See poster by D. Brown
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Stephen C. Johnson forthe PHENIX Collaboration
Special Thanks
R. SoltzM. Heffner