Transcript Charged Kaon Correlations

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

HBT : Probing source geometry
p source
(x)
x2
5 fm
p1
r1
1m
p2
T 
1 {
2
  i(r1  x 1 )p1   i(r2  x 2 )p 2
U(x1, p1 )e
U(x 2 , p2 )e
  i( r1  x 2 )p1   i( r2  x 1 )p 2
 U(x 2 , p1)e
U(x1, p2 )e
}
r2

*TT  U1*U1  U*2 U 2  1  eiq( x1  x 2 )
2-particle probability
P(p1, p 2 )
2
C(p1, p 2 ) 
 1 ~
 (q )
P(p1 )P(p 2 )
1-particle probability
(x,p) = U*U
C (Qinv)
x1

  
q  p 2  p1
Width ~ 1/R
2
1
Measurable!
F.T. of particle source
0.05
0.10
Qinv (GeV/c)
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.
electrons
K0s K0s HBT extends particle
correlation systematics to
higher pt
No conclusive measurements so far
F. Antinori et al. Nucl. Phys. A661 (1999) 130c
WA9
7
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 < 0.45 GeV
for Mt dependence
0.15 GeV < kT < 0.35 GeV
0.35 GeV < kT < 0.45 GeV
Fitting the correlation functions
Standard fit
A( q )
 N  (1    G ( q ))
B ( q )  K coul ( q )
Bowler/Synukov/CERES
A( q )
 N  1    K coul ( q )  1  G ( q )  1
B(q)
where
G(q)  e
  Rij2 qi q j
i, j
Gaussian form
K coul ( q )
" undiluted" CoulombCorrection(K coul  1)
N
A( q )
normalization constant
" real"pair distribution
B(q)
" mixedevent"pair distribution
Fits to 1D correlation functions
K-K-
K-K-
Lambda = 0.333 +- 0.04
Rinv = 3.72 +- 0.1 fm
K-K-
What coulomb radius is used for the
correction does not seem to make much
difference .
Projections of 3D fits using the standard procedure
Out
(qSide, qLong < 45 MeV)
Side (qOut, qLong < 45 MeV)
K- K-
Long
(qSide, qOut < 45 MeV)
K- K-
A(q)
 N  (1    G (q))
B(q)  K coul (q)
Lambda = 0.5096 +- 0.0168
Ro = 2.942 +- 0.0685 fm
Rs = 2.97 +- 0.0668fm
Rl = 3.29 +- 0.764 fm
K- K-
Projections of 3D fits using the Bowler/Synukov
procedure
Out
(qSide, qLong < 45 MeV)
K- K-
Long
Side
A( q )
 N  1    K coul ( q )  1  G ( q )  1
B(q)
(qOut, qLong < 45 MeV)
K- K-
(qSide, qOut < 45 MeV)
K- K-
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 !
No corrections for purity and
momentum resolution
K0s Reconstruction
Vo
decay length
dca of V0 to
primary vertex
dca between
daughters
dca of daughters
to primary vertex
V0 Cuts
DCA – distance of closest approach
central events
0.1 < pt < 3.5
-1.5 < y < 1.5
s
mass peak (Not Background subtracted)
X 10
Number of events
K0
K0s multiplicity
Mean ~ 3.79 / Event
Number of K0s
K0sK0s Correlation Function
M (GeV/C2)
Fitting to a gaussian
C ( P, q)  1   exp(  R 2 q 2 )
Gives the values
Lambda = 0.506 0.133
Rinv = 5.765  0.691
C2
Signal to Noise studies
Signal + Background
Signal
Background
1)
2)
Signal
3)
Lorentzian
Background
1) a+bx
2 ) a + b xc
3 ) a/x + b/(1 + x)
Needs more study
pions
K-
Ro
Rs
Rl
Hydro Mt scaling seems to be
obeyed for the charged pions
and Kaons.
Mt Scaling violated?
pions
KK0s
R
Rinv for the neutral Kaons
seems to indicate that Mt
scaling is not obeyed as
for the charged pions and
Kaons.
Mt (Gev/c)
What is the effect of the
0
f (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
Ratio of f0(980) to K0s as a function of temperature
1
4pp dp
2
2
ni 
,
E

p

m
i
i
(2p )3  e( Ei / T )  1
2
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
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
Results from a gaussian fit
The radius changes by a small
amount while the lambda seems to be
affected most.
Summary
 1D and 3D correlations of Charged Kaons

preliminary results

Not yet corrected for purity and momentum resolution
K-
KLambda = 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!
 1D K0sK0s correlations

preliminary results


Not corrected for purity and momentum resolution
The f0(980) effect seems to be small
Lambda = 0.506 0.133
Rinv = 5.765  0.691
Outlook
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
Hopefully new results in the near future