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First Results on Two-Particle Correlations Determined by PHENIX. Stephen C. Johnson Lawrence Livermore National Lab for the PHENIX Collaboration. C 2. 1/R. q. Why study particle correlations? (Preaching to the choir). p 1. - PowerPoint PPT Presentation
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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
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
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.
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.
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
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
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
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
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
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
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
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
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
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
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…
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
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
Stephen C. Johnson forthe PHENIX Collaboration
Special Thanks
R. SoltzM. Heffner