first results from star experiment at rhic - soft hadron physics -

Masashi Kaneta, LBNL

Masashi Kanetafor the STAR collaboration

Lawrence Berkeley National Lab.

First results from STAR experiment at RHIC- Soft hadron physics -


Focus onHadrons

Measured : h, ±, K±, K0s, K*0, K*0, p, p, d, 3He, 3He,

t,In future : 0 +’, , 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


Spectra


Spectra

Momentum distributionsInformation of thermal (kinetic) freeze-out

The inverse slope parameter of mT distribution reflects temperature and radial flow


Only stat. errors are shown

p

K-

central collisions

6%11-1

8%

26-3

4%

45-5

8%

58-8

5%

Identified particle spectra

p

K-

central collisions

6%11-1

8%

26-3

4%

45-5

8%

58-8

5%

Only stat. errors are shown


Thermal(Kinetic) freeze-out

Thermal freeze-out at RHICTemperature is similar at SPSLarger radial flow than at SPS

STAR (sNN=130 GeV)

c

T fo

60.0

MeV95

Hydrodynamical model: E. Schnedermann et al.PRC48(1993)2462

mT-mass [GeV/c2]

mass [GeV/c2]

Inve

rse

slop

e pa

ram

eter

[G

eV/c

2 ]


Ratios


Ratios

pT dependence anti-particle/particleTest slope for particle and anti-particle

Anti-baryon/baryon ratioStopping or transparent?

Particle ratios from hadronsChemical freeze-out parameters


p/p ratio

Minimum bias dataNo or weak pT dependence

Submitted to PRLSystematic errors<10%


/ ratio

No significant pT dependence in the ratio

The mean ratio = 0.72±0.04

From 200 K Central trigger Au+Au Events (top ~15% multiplicity.)

Systematic errors are under evaluation

|y|<0.5

r

atio


K+/K ratiora

tio

pT [GeV/c]

STAR Preliminary

|y|<0.5Event fraction = top 7%


Multiplicity dependence of ratios

Not baryon free at mid-rapidity

An effect of anti-baryon absorption in central collisions?

(nch/nmax)

/ Preliminary

Preliminary

P e r i p h e r a l C e n t r a l

p/p submitted to PRL pT 0.6-0.8 GeV/c |y|<0.3

Only statistic errors are shown Systematic errors p/p : 10%

and : under evaluation

ratio


Chemical freeze-out

Baryonic Potential B [MeV]

Chem

ical Tem

pera

ture

Tch

[M

eV

]

0

200

250

150

100

50

0 200 400 600 800 1000 1200

AGS

SIS

LEP/

SppS

SPS

quarks-gluons

hadrons

RHIC

Experimental ratio

Mod

el p

redi

ctio

n of

rat

io

48±12B


HBT


HBT

Pion HBTCentralityTransverse momentumThe HBT excitation function

Phase space densityEvent-by-Event HBTK0

s K0s,

pp, pp correlationsNon-identical particles

Many topics in STAR measurement

The HBT excitation function Focus in this talk


The HBT excitation function

Compilation 3D -HBT parameters as a function of s

• ~10% Central Au+Au(Pb+Pb) events• y ~ 0 • kT 0.17 GeV/c

STAR PreliminaryNo significant jump

from SPS to RHICWe need energy scan between both energy


EventAnisotropy


Event anisotropy

In momentum spaceAnisotropy measured as second harmonic parameter v2

v2 will be scale to initial shape parameter ,

if the source has a hydrodynamical expansion

x

y

p

patan2cos2 v

Momentum space

Almond shape overlap region in coordinate space

y2 x2 y2 x2


Charged particle v2 versus Multiplicity

PRL 86, (2001) 402

|| < 1.3

0.1 < pT < 2.0

Boxes show “initial spatial anisotropy” scaled by 0.19-0.25

nch = primary tracks in || < 0.75


Charged and p+p, v2(pT) (M.B.)


Comparison with a hydrodynamical model

Hydrodynamical calculations: Huovinen, Kolb and Heinz


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


Summary

Net-baryon 0 at mid-rapidityAnti-baryon/baryon ratios are toward 1, but still <1

Chemical Freeze-outTch : same or higher than at SPS

B ： smaller than at SPS

HBT parametersSimilar to SPS

Large anisotropic flowFrom mid-central to central data,Hydrodynamical model can describe v2 at low pT (<2GeV/c)

Thermal Freeze-outTfo : similar to SPS/AGSLarge radial flow

We need energy scan between SPS and RHIC!


Future plansTOF

PID up to 2GeV/c of pT

SVTIncreasing momentum resolutionMore strangeness baryons

EMCElectron measurement

Full fieldsHigher pT measurementIncreasing momentum resolution

With high statistics

Physics of0, and resonances


Typical e+e pairfrom

e+

e+

e+

e+

e-

e-

e-e-

invariant mass [GeV]

STAR Preliminary

and0

The e+e pair from conversion is measured

Large acceptance pT = 50 MeV/c to ~4 GeV/c, ||<1.8

first results from star experiment at rhic - soft hadron physics -

Documents