Transcript First results from STAR experiment at RHIC

First results from STAR
experiment at RHIC
- Soft hadron physics -
Masashi Kaneta
for the STAR collaboration
Lawrence Berkeley National Lab.
Masashi Kaneta, LBNL
Focus on
Hadrons
Measured : h-, p ±, K±, K0s, K*0, K*0, p, p, d, 3He, 3He,
t, L, L, X -, X +,
In future : p 0, f, W -+W - , r, w, h, h’, D, L(1520),
S(1385), J/ and more
Freeze-out conditions of low momentum
hadrons by
Spectra/Ratios
• Thermal/Chemical Freeze-out
Particle correlations
• Size parameters, Phase space density
Event anisotropy
• v2
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Spectra
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Spectra
Momentum distributions
Information of thermal (kinetic)
freeze-out
The inverse slope parameter of mT
distribution reflects temperature
and radial flow
Masashi Kaneta, LBNL
Identified particle spectra
Only stat. errors
are shown
Only stat. errors
are shown
central collisions

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6%
11-18%
26-34%
central collisions 
6%
11-18%
p
26-34%
K-
58-85%
45-58%
p
45-58%
58-85%
K-
Inverse slope parameter [GeV/c2]
Thermal(Kinetic) freeze-out
STAR (sNN=130 GeV)
T fo  95 MeV
   0.60 c
Hydrodynamical model:
E. Schnedermann et al.
PRC48(1993)2462
mass [GeV/c2]
Thermal freeze-out at RHIC
mT-mass [GeV/c2]
Temperature is similar at SPS
Larger radial flow than at SPS
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Ratios
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Ratios
pT dependence anti-particle/particle
Test slope for particle and anti-particle
Anti-baryon/baryon ratio
Stopping or transparent?
Particle ratios from hadrons
Chemical freeze-out parameters
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p/p ratio
Minimum bias data
No or weak pT dependence
Submitted to PRL
Systematic errors<10%
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L/L ratio
No significant pT
dependence in the
ratio
L/L ratio
The mean ratio
= 0.72±0.04
|y|<0.5
From 200 K Central trigger Au+Au
Events (top ~15% multiplicity.)
Systematic errors are under
evaluation
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+
-
ratio
K /K ratio
|y|<0.5
Event fraction = top 7%
pT [GeV/c]
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Multiplicity dependence of ratios
L/L Preliminary
ratio
X+/X- Preliminary
Only statistic errors are shown
Systematic errors
p/p : 10%
L/L and X+/X- : under evaluation
p/p submitted to PRL
pT 0.6-0.8 GeV/c
|y|<0.3
Peripheral  Central
(nch/nmax)
Not baryon free at mid-rapidity
An effect of anti-baryon absorption in
central collisions?
Masashi Kaneta, LBNL
Model prediction of ratio
Chemical freeze-out
Chemical Temperature Tch [MeV]
250
quarks-gluons
RHIC
200
SPS
150
B 48±12
AGS
Experimental ratio
100
SIS
50
hadrons
0
0
200
400
600
800
1000
1200
Baryonic Potential B [MeV]
Masashi Kaneta, LBNL
Masashi Kaneta, LBNL
HBT
Many topics in STAR measurement
Pion HBT
Centrality
Transverse momentum
The HBT
excitation
function
The
HBT
excitation
function
Focus in
this talk
Phase space density
Event-by-Event HBT
K0s K0s, LL
pp, pp
ppp correlations
Non-identical particles
Masashi Kaneta, LBNL
The HBT excitation function
Compilation 3D pp-HBT
parameters as a function of s
• ~10% Central Au+Au(Pb+Pb)
events
•y~0
• kT 0.17 GeV/c
No significant jump
from SPS to RHIC
We need energy scan
between both energy
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Event
Anisotropy
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Event anisotropy
In momentum space
Momentum space
Anisotropy measured as second
harmonic parameter v2
v2  cos2f
f  atan
py
px
v2 will be scale to initial shape
parameter e,
if the source has a
hydrodynamical expansion
Almond shape
overlap region in
coordinate space
y 2 - x 2 
e 2
y + x 2 
Masashi Kaneta, LBNL
Charged particle v2 versus Multiplicity
Boxes show
“initial spatial
anisotropy” e
scaled by 0.190.25
PRL 86, (2001) 402
|h| < 1.3
0.1 < pT < 2.0
nch = primary tracks in |h| < 0.75
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Charged p and p+p, v2(pT) (M.B.)
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Comparison with a hydrodynamical model
Hydrodynamical calculations: Huovinen, Kolb and Heinz
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Charged particle anisotropy 0<pT<4.5 GeV/c
Minimum bias data
Only statistical errors
Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c
Masashi Kaneta, LBNL
Summary
Net-baryon  0 at mid-rapidity
Anti-baryon/baryon ratios are toward 1, but still <1
Chemical Freeze-out
Tch : same or higher than at SPS
B ：smaller than at SPS
HBT parameters
Similar to SPS
Large anisotropic flow
From mid-central to central data,
Hydrodynamical model can describe v2 at low pT (<2GeV/c)
Thermal Freeze-out
Tfo : similar to SPS/AGS
Large radial flow
We need energy scan between SPS and RHIC!
Masashi Kaneta, LBNL
Future plans
TOF
PID up to 2GeV/c of pT
SVT
Increasing momentum resolution
More strangeness baryons
EMC
Electron measurement
Full fields
Higher pT measurement
Increasing momentum resolution
With high statistics
Physics of g, p0, and resonances
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g and
0
p
The e+e- pair from g conversion is measured
Large g acceptance
pT = 50 MeV/c to ~4 GeV/c, |h|<1.8
Typical e+e- pair
from g
e+
STAR Preliminary
e+
e-
e- e-
e+
p0
ee+
gg invariant mass [GeV]
Masashi Kaneta, LBNL