1. 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

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

3. Measurable! F.T. of pion source 1 m r1r1 r2r2 p1p1 p2p2  source  (x) x1x1 x2x2 5 fm 1-particle probability  (x,p) = U * U 2-particle probability HBT : Probing source geometry

4. 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 -K 0 s K 0 s HBT extends particle correlation systematics to higher pt allowing studies of Mt scaling, collective flow effects etc.

5. K 0 s K 0 s HBT extends particle correlation systematics to higher pt WA9 7 F. Antinori et al. Nucl. Phys. A661 (1999) 130c No conclusive measurements so far protons kaons pions electrons

6. Charged Kaon Cuts Main Cuts central events -0.5 < y < 0.5 for 1D correlations 0.25 GeV < kT < 0.45 GeV for 3D correlations 0.15 GeV < kT < 0.35 GeV 0.35 GeV < kT < 0.45 GeV

7. Standard fit Bowler/Synukov/CERES where Fitting the correlation functions

8. STAR Preliminary Fits to 1D correlation functions What coulomb radius is used for the correction does not seem to make much difference. Lambda = 0.333 +- 0.04 R inv = 3.72 +- 0.1 fm K-K- STAR Preliminary

9. Out Side Long (qOut, qLong < 45 MeV) (qSide, qLong < 45 MeV) (qSide, qOut < 45 MeV) Projections of 3D fits using the standard procedure Lambda = 0.5096 +- 0.0168 R o = 2.942 +- 0.0685 fm R s = 2.97 +- 0.0668fm R l = 3.29 +- 0.764 fm K-

10. Lambda = 0.2871 +- 0.025 R o = 3.62 +- 0.145 fm R s = 3.21 +- 0.134 fm R l = 3.92 +- 0.154 fm Lambda is small for the Bowler correction ! Out Side Long (qSide, qLong < 45 MeV) (qSide, qOut < 45 MeV) (qOut, qLong < 45 MeV) Projections of 3D fits using the Bowler/Synukov procedure No corrections for purity and momentum resolution K- STAR Preliminary

11. K 0 s Reconstruction VoVo dca between daughters dca of daughters to primary vertex dca of V 0 to primary vertex decay length DCA – distance of closest approach V0 Cuts central events 0.1 < pt < 3.5 -1.5 < y < 1.5

12. K 0 s K 0 s Correlation Function C2 STAR Preliminary Gives the values Lambda = 0.506  0.133 R inv = 5.765  0.691 Fitting to a gaussian K 0 s mass peak (Not Background subtracted) X 10 M (GeV/C 2 ) Number of K 0 s Mean ~ 3.79 / Event Number of events K 0 s multiplicity

13. 1) 2) 3) Signal Lorentzian Background 1 ) a + b x 2 ) a + b x c 3 ) a/x + b/(1 + x) Needs more study Signal + Background Signal Background Signal to Noise studies

14. pions K- RoRo RsRs RlRl Hydro M t scaling seems to be obeyed for the charged pions and Kaons. STAR Preliminary

15. M t Scaling violated? R inv for the neutral Kaons seems to indicate that M t scaling is not obeyed as for the charged pions and Kaons. pions K- K 0 s M t (Gev/c) R STAR Preliminary

16. What is the effect of the f 0 (980)? Mass of f 0 (980) = 980 +- 10 MeV width = 40 - 100 MeV. => lifetime ranges between 1.97 fm/c and 4.93 fm/c Dominant decay mode is pions Branching ratio to kaons is unknown

17. Only those f 0 s which fall in the shaded region can decay to K 0 s, since the mass of a K 0 s is 0.498 GeV Ratio of f 0 (980) to K 0 s as a function of temperature f 0 s are selected from a Briet-wigner mass distribution M = 0.996

18. Correlation function for a pure K 0 sample The effect of the f 0 particle assuming the worst case scenario where its decay products are only kaons

19. Results from a gaussian fit The radius changes by a small amount while the lambda seems to be affected most.

20. 1D and 3D correlations of Charged Kaons preliminary results Not yet corrected for purity and momentum resolution 1D K 0 s K 0 s correlations preliminary results Not corrected for purity and momentum resolution The f 0 (980) effect seems to be small Summary Lambda = 0.2871 +- 0.025 R o = 3.62 +- 0145 fm R s = 3.21 +- 0.134 fm R l = 3.92 +- 0.154 fm Lambda is small for the Bowler procedure! Lambda = 0.506  0.133 R inv = 5.765  0.691 Lambda = 0.333 +- 0.04 R inv = 3.72 +- 0.1 fm K-K- K-K-

21. Charged Kaon correlations we need to do more systematic studies purity estimate/correction momentum resolution with more statistics Multiplicity dependence Neutral Kaon correlations we need to do purity estimate/correction momentum resolution Outlook Hopefully new results by next Analysis Meeting