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

Outline

Motivation Charged Kaons

cuts 1D correlations 3D correlations

Neutral Kaons cuts C2 The f0(980) problem

Summary Outlook

2

21

2121 )q(~1

)p(P)p(P)p,p(P)p,p(C C

(Qin

v)

Qinv (GeV/c)

1

2

0.05 0.10

Width ~ 1/R

Measurable! F.T. of pion source

222111 p)xri(22

p)xri(11 )p,xU()p,x U(

eeT1 m

r1

r2

p1

p2

source(x)

x1

x2

{2

1

}e)p,x(Ue)p,x(U 212121 p)xr(i21

p)xr(i12

5 fm

12 ppq 1-particle probability

(x,p) = U*U

)xx(iq2

*21

*1T

*T

21e1UUUU

2-particle probability

HBT : Probing source geometry

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 K0

s HBT extends particle correlation systematics to higher pt allowing studies

of Mt scaling, collective flow effects etc.

K0s K0

s HBT extends particle correlation systematics to higher pt

WA97

F. Antinori et al. Nucl. Phys. A661 (1999) 130c

No conclusive measurements so far

protons

kaons

pions

electrons

Charged Kaon Cuts

Main Cutscentral 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

1)(1)(1)()(

qGqKNqBqA

coul

))(1()()(

)( qGNqKqB

qA

coul

Standard fit

ondistributipair event" mixed")(ondistributipair real"")(

constantion normalizat

)1coul(K Correction Coulomb undiluted"")(formGaussian

,2

)(

qBqAN

qcoulK

ji jqiqijReqG

Bowler/Synukov/CERES

where

Fitting the correlation functions

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 +- 0.04Rinv = 3.72 +- 0.1 fm

K-K-

K-K-K-K-

STAR Prelim

inary

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 +- 0.0168Ro = 2.942 +- 0.0685 fmRs = 2.97 +- 0.0668fmRl = 3.29 +- 0.764 fm

))(1()()(

)( qGNqKqB

qA

coul

K- K-

K- K-

K- K-

Lambda = 0.2871 +- 0.025Ro = 3.62 +- 0.145 fmRs = 3.21 +- 0.134 fmRl = 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

1)(1)(1)()(

qGqKNqBqA

coul

K- K-

K- K-

K- K-

STAR Prelim

inary

K0s Reconstruction

Vo

dca between daughters

dca of daughters to primary vertex

dca of V0 to primary vertex

decay length

DCA – distance of closest approach

V0 Cuts

central events 0.1 < pt < 3.5 -1.5 < y < 1.5

K0sK0

s Correlation Function

C2

STAR Prelim

inary

Gives the values

Lambda = 0.506 0.133 Rinv = 5.765 0.691

)exp(1),( 22qRqPC

Fitting to a gaussian

K0s mass peak (Not Background subtracted)

X 10

M (GeV/C2)

Number of K0s

Mean ~ 3.79 / Event

Num

ber o

f eve

nts K0

s multiplicity

1) 2)

3)Signal Lorentzian

Background 1 ) a + b x 2 ) a + b xc

3 ) a/x + b/(1 + x)

Needs more study

Signal + BackgroundSignal

Background

Signal to Noise studies

pions K-

Ro

Rs

Rl

Hydro Mt scaling seems to be obeyed for the charged pions and Kaons.

STAR Prelim

inary

Mt Scaling violated?

Rinv for the neutral Kaons seems to indicate that Mt scaling is not obeyed as for the charged pions and Kaons.

pions K- K0

s

Mt (Gev/c)

R STAR Prelim

inary

What is the effect of the f0(980)?

Mass of f0(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

Only those f0s which fall in the shaded region can decay to K0s, since the mass of a K0s is 0.498 GeV

, 1

4)2(

1 22)/(

2

3 iiTEi mpEe

dppni

Ratio of f0(980) to K0s as a function of temperature

f0s are selected from a Briet-wigner mass distribution

M = 0.996

Correlation function for a pure K0 sample

The effect of the f0 particleassuming the worst case scenario where its decay products are only kaons

Results from a gaussian fit

The radius changes by a small amount while the lambda seems to be affected most.

1D and 3D correlations of Charged Kaons preliminary results

Not yet corrected for purity and momentum resolution

1D K0sK0

s correlations preliminary results

Not corrected for purity and momentum resolution The f0(980) effect seems to be small

Summary

Lambda = 0.2871 +- 0.025Ro = 3.62 +- 0145 fmRs = 3.21 +- 0.134 fmRl = 3.92 +- 0.154 fm

Lambda is small for the Bowler procedure!

Lambda = 0.506 0.133 Rinv = 5.765 0.691

Lambda = 0.333 +- 0.04Rinv = 3.72 +- 0.1 fm

K-K-

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