Transcript Kaon production at s experiment

Kaon production at
sNN = 200 GeV
measured with the PHENIX
experiment
Momchil Velkovsky
SUNY at Stony Brook
For the PHENIX collaboration
What do we learn from K ?
From the p, K, p spectra: kinetic freeze
out conditions .
From K / K+: chemical potentials and
strangeness production mechanism.
Is it thermal?
Can shed light on the p suppression
versus p non-suppression puzzle at the
2-4 GeV pT range.
Is it a baryon or a mass effect?
PHENIX
PHENIX Detector
at Collision Point
East Carriage
Being Moved in Place
Ring Imaging Cerenkov
Drift Chamber
Beam-Beam Counter
Central Magnet
West Carriage
PHENIX PID
 sTOF =120ps, K/p separation pT<2GeV/c
Corrections: decay in flight, acceptance,
reconstruction efficiency, multiplicity
dependent corrections ( embedding)
Kaon pT spectra
Mid rapidity, |y|<0.35
K+
Kcentrality
PHENIX Preliminary
PHENIX Preliminary
Characterized by mT exponential shape for all centralities
0- 5%
5 - 10 %
10 - 15 %
15 - 20 %
20 - 30 %
30 - 40 %
40 - 50 %
50 - 60 %
60 - 70 %
70 - 80 %
80 - 91 %
Freeze-out parameters
Simultaneous fit in range (mt -m0 ) < 1 GeV is shown. The top 5 centralities are scaled .
For the 5% central:
For the 80%-91% peripheral:
T = 0.5 0.2 syst. (< T> = 0.3 ± 0.2 syst. ) T = 0.7 ± 0.2 syst. (< T> = 0.5 ± 0.2 syst.)
Tfo = 135 23 MeV
Tfo = 110 23 MeV


<pT> vs. Npart
Syst.
error :
p (10%),
K (15%),
p (14%)
Increase of <pT> as a function of Npart and tends to saturate
p < K < p (p)
Only one parameter in the model: the initial pT kick.
-
Au+Au at
s NN =200GeV
K /K+
Centra
l
Flat pT dependence
Ratio close to 1
No centrality dependence
Somewhat lower in p-p
(comparable within errors)
Au+Au at
s NN =200GeV
Peripheral
p-p data (200 GeV)
Au+Au at
s NN =200GeV
p/p ratio
Central
 Flat pT dependence for
central events.
 Decreasing for
peripheral > 2.5 GeV?
p-p consistent with it
Au+Au at
s NN =200GeV
Peripheral
Estimate of Baryon Potential
Statistical thermal model
hep-ph/0002267 F.Becattini et al.
PHENIX preliminary (200 GeV),
central (0-10%)
(130GeV)
p-
p+
 /
= 1.02  0.02 (stat)  0.1 (sys)
 K- / K+ = 0.92  0.03 (stat)  0.1(sys)
 p / p = 0.70  0.04 (stat)  0.1(sys)
Baryon chemical potential :
mB~ 30MeV at 200 GeV
mB~ 46MeV at 130 GeV
dN/dy per participant pair
Au+Au at



s NN =200GeV
p-
p-
p
p
Pion production almost linear with Npart
Kaon production raises faster than Npart
Hydro model fails for Npart < 100
K/pi versus Npart
syst.
error
12%
Rising with Npart ,
Similar behaviour observed at AGS and SPS
K0s measurement in PHENIXmotivation
 Pions are suppressed, p, p up to 4 GeV/c are not
 Is this due to their masses or to the hadronization
mechanism (baryons vs. mesons)?
 Like p0, K0s can be extended to high pT.
K0s measurement in PHENIX
Br (K0s p+p-)=68.8%
Search for p+p- pairs with invariant
mass around m(K0s)=497.7 MeV
Mix events with the same centrality and
vertex. Do pair cuts.
K0s p+pcentral
+foreground
+background
m (GeV)
K0s p+pcentral
subtracted
m (GeV)
Conclusions
 From the measured p+,p-,K+,K-,p,p spectra:
T=0.70.2, TFO=110 23 MeV, mB~30 MeV for the
most central events at s =200 GeV
 The K+/K- ratio is flat in pT and centrality,
consistent with thermal production
 K yield grows faster than Npart and faster than p
 Hydrodynamic models describe anti-proton <pT>,
but fail for meson dN/dy, <pT> and the K/p ratio in
peripheral events (Npart<150)
 Measuring K0s up to high pT will shed light on the
p-p puzzle.

Extra slides
The Parameters Tfo and T vs. Npart
• Expansion parameters
in each centrality
• Overall systematic
uncertainty is shown.
• A trend with
increasing Npart is
observed:
– Tfo and
T
• Saturates at midcentral