Charged Kaon Correlations

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Charged and Neutral Kaon correlations in Au-Au
Collisions at sqrt(s_NN) 200 GeV using the
solenoidal tracker at RHIC (STAR) Selemon
Bekele The Ohio State University for the STAR
Collaboration
SQM2003 March 12-17, 2003
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Outline

• Motivation
• Charged Kaons
• cuts
• 1D correlations
• 3D correlations
• Neutral Kaons
• cuts
• C2
• The f0(980) problem
• Summary
• Outlook

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Motivation

• Physics
• -Kaon HBT has been suggested as a promising
  probe of QGP
• -Kaon HBT reveals information about strangeness
  dynamics
• M. Gyulassy, Phys. Lett B 286 (1992) 211
• -Kaons are less affected by decay of long lived
  resonances
• Technical
• -No distortions due to Coulomb
  interaction
• -K0s K0s HBT extends particle correlation
  systematics to higher pt allowing studies
• of Mt scaling, collective flow effects etc.

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protons
kaons
pions
electrons
K0s K0s HBT extends particle correlation
systematics to higher pt
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Charged Kaon Cuts Main Cuts central events
-0.5 lt y lt 0.5 for 1D correlations
0.25 GeV lt kT lt 0.45 GeV for 3D
correlations 0.15 GeV lt kT lt
0.35 GeV 0.35 GeV lt kT lt 0.45 GeV

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Fitting the correlation functions
Standard fit
Bowler/Synukov/CERES
where
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Fits to 1D correlation functions
K-K-
K-K-
Lambda 0.333 - 0.04 Rinv 3.72 - 0.1 fm
STAR Preliminary
K-K-
STAR Preliminary
What coulomb radius is used for the correction
does not seem to make much difference .
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Projections of 3D fits using the standard
procedure
K- K-
K- K-
K- K-
Lambda 0.5096 - 0.0168 Ro 2.942 - 0.0685
fm Rs 2.97 - 0.0668fm Rl 3.29 - 0.764 fm
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Projections of 3D fits using the Bowler/Synukov
procedure
K- K-
K- K-
STAR Preliminary
Lambda 0.2871 - 0.025 Ro 3.62 - 0.145
fm Rs 3.21 - 0.134 fm Rl 3.92 - 0.154 fm
Lambda is small for the Bowler correction !
K- K-
No corrections for purity and momentum resolution
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K0s Reconstruction
Vo
V0 Cuts central events 0.1 lt pt lt 3.5
-1.5 lt y lt 1.5
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K0sK0s Correlation Function
K0s mass peak (Not Background subtracted)
STAR Preliminary
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Signal to Noise studies
Signal Background Signal Background
1)
2)
Signal Lorentzian Background 1 ) a b x
2 ) a b xc 3 ) a/x b/(1 x) Needs
more study
3)
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pions K-
Ro
STAR Preliminary
Hydro Mt scaling seems to be obeyed for the
charged pions and Kaons.
Rs
Rl
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Mt Scaling violated?
STAR Preliminary
Rinv for the neutral Kaons seems to indicate
that Mt scaling is not obeyed as for the charged
pions and Kaons.
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What is the effect of the f0(980)?
Mass of f0(980) 980 - 10 MeV width 40 -
100 MeV. gt lifetime ranges between 1.97 fm/c
and 4.93 fm/c Dominant decay mode is
pions Branching ratio to kaons is unknown
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Ratio of f0(980) to K0s as a function of
temperature
f0s are selected from a Briet-wigner mass
distribution
Only those f0s which fall in the shaded region
can decay to K0s, since the mass of a K0s is
0.498 GeV
M 0.996
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Correlation function for a pure K0 sample
The effect of the f0 particle assuming the worst
case scenario where its decay products are only
kaons
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Results from a gaussian fit
The radius changes by a small amount while the
lambda seems to be affected most.
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Summary

• 1D and 3D correlations of Charged Kaons
• preliminary results
• Not yet corrected for purity and momentum
  resolution
• 1D K0sK0s correlations
• preliminary results
• Not corrected for purity and momentum resolution
• The f0(980) effect seems to be small

K-
K-
Lambda 0.333 - 0.04 Rinv 3.72 - 0.1 fm
Lambda 0.2871 - 0.025 Ro 3.62 - 0145 fm Rs
3.21 - 0.134 fm Rl 3.92 - 0.154 fm Lambda
is small for the Bowler procedure!
Lambda 0.506? 0.133 Rinv 5.765 ? 0.691
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