Masashi Kaneta, LBNL Masashi Kaneta for the STAR collaboration First results from STAR experiment at...

Masashi Kaneta, LBNL

Masashi Kanetafor the STAR collaboration

First results from STAR experiment at RHIC

Lawrence Berkeley National Lab.


The STAR collaboration

~ 400 collaborators 34 institutions 7 countries


STAR InstitutionsU.S. Labs:

Argonne, Berkeley, and

Brookhaven National Labs

U.S. Universities:

Arkansas, UC Berkeley,

UC Davis, UCLA,

Carnegie Mellon, Creighton,

Indiana, Johns Hopkins,

Kent State, MIT, MSU,

CCNY, Ohio State,

Penn State, Purdue, Rice,

UT Austin, Washington,

Wayne State, Yale

Brazil :

Universidade de Sao Paol

England:

University of Birmingham

France:

Institut de Recherches Subatomiques Strasbourg, SUBATECH – Nantes

Germany:

Max Planck Institute – Munich, University of Frankfurt

Poland:

Warsaw University Warsaw University of Technology

Russia:

MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino


STAR DetectorYear1 Ready for next run Next year(2002) or later

ZDC

Silicon Vertex Tracker

Central Trigger Barrel

FTPCs

Barrel EMC (install over next 4 years)

Vertex Position Detectors

Endcap EMC (half in 2003)

Magnet

Coils

TPC Endcap & MWPC

ZDC

RICH

yr.1 SVT ladder

+ TOF patch

Silicon Strip Detector

Time Projection Chamber


Au+Au, sNN=130 GeV

Central EventFrom real-time Level 3 display.

~2000 tracks in 200msec


Particle identification

K

p

e


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

Low pT spectra

h, , K, p Thermal freeze-out

High pT spectra

hhard process

Particle ratios, yield (dN/dy, dN/d)p/p, , , K/K, K/, p/, K*0/h

Stopping Chemical freeze-out

d/p Coalescence


h- multiplicity

6% systematic error shown on 3 points only

Preliminary

5% Central

ZD

C p

ulse

hei

ght

CTB pulse height


h- centrality dependence

5%

10%

20%

30%

40%


h- centrality dependence (cont.)

15% Increase in <pT> from 80% sample to top 5% central

NA49UA1

STAR, Preliminary

STAR, Preliminary


h- pT distribution

STAR Preliminary

Statistical errors negligibleErrors on points: systematic error on STAR dataGray bars: cumulative error including UA1 scalingHard: Binary collisions TAA = 26 ± 2 mb-1

Soft: Wounded nucleon

STAR Preliminary


Particle Identification

dE/dxe, , K, p

Kink, V0, Mixed eventKaon to muon decay, etc.Resonances

Kd

e

p

“kinks”:

K +

Vo


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


K+K-


Identified particle spectra

Inverse slope:56540(sta.)50(sys.) MeV


-

K-p


central collisions


Inverse slope vs. centrality

K- (kink)

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

STAR Preliminary Indicate increased radial flow in central collisions at RHIC

Event fraction [%]


Kink K

Kaon from muon decay

K



K-K+

|y|<0.5Event fraction = top 7%

STAR Preliminary STAR Preliminary



“Kink” Rapidity Distribution

Mid-y K+ dN/dy = 35 ±3(stat.)±5(sys.)

Mid-y K- dN/dy = 30±2.5(stat.)±4(sys.)


mT distribution from Hydro model

Cylindrical source

Flow profile included

u t r z er ( , , ) (cosh , sinh , )= =

β= −tanh 1r ( )β βr s r R= /

R

βs

Ref. : E.Schnedermann et al, PR C48 (1993) 2462


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

>=<

=

β

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


p/p ratioMinimum bias dataSystematic errors<10% for bothNo or weak pT and rapidity dependence

rapidity

STAR submittedSTAR submitted


and

~0.84 /event, ~ 0.61/event

V0Mixed event

Higher statistics than V0 method (~10 times/event)

Invariant mass [GeV] Invariant mass [GeV]

Top 15% central event

Minimum Bias (150K event)

0<p<2GeV/c

STAR submitted


/ 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

ra

tio


K+/K ratiora

tio

pT [GeV/c]

STAR Preliminary



+ and -


Centrality dependence of ratios

An effect of anti-baryon absorption in central collisions?

(nch/nmax)

/ Preliminary

Preliminary


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


Centrality dependence of ratios (cont.)

K+/K ratio seems to be independent of centrality in each measurement

STAR preliminary

dE/dx KinksSTAR preliminarypT < 0.35 GeV/c

# primary trackdN/d

K+/K

rat

io

K+/K

rat

io

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


K/ and p/ ratios

K-/- , p/-

enhanced by ~2 in central vs. peripheral collisions

p/K ~ constant

In central collisions:

K-/- 15%

p/- 8%



K*0K++-

Central events (top 14%)

primary tracks: K+-

K* signalmK*0 = 0.8930.003 [GeV]

K*0 = 0.058 0.015 [GeV] (stat. error only)

PDG mK*0 = 0.89610.00026 [GeV] K*0 = 0.05070.0006 [GeV]

Background estimate: 20%

Breit-Wigner

)4/)((2 220 +−

MmA


K*0K-++

Central events (top 14%)

primary tracks: K-+

K* signalmK*0 = 0.8960.004 [GeV]

K*0 = 0.063 0.011[GeV] (stat. error only)

PDG mK*0 = 0.89610.00026 [GeV] K*0 = 0.05070.0006 [GeV]

Background estimate: 18%

Breit-Wigner

)4/)((2 220 +−

MmA


K*0

The first measurement of K*0 in heavy ion collisionsK

*0/h

K*0/h

(K*0 +K*0)/2 / h

Centrality h/hmax

K*0/hSTAR preliminary

Only statistical errors are shownSystematic error ~ 25%

|y|<0.50.2<pT<2.0 GeV/c

pp (s=63GeV) : K*0/

e+e (s=91GeV) : K*0/

h : ||<0.5 pT>0.1 GeV/c



Summary of ratios

Anti-particle/particle ratio is flat as a function of pT

Anti-baryon/baryon ratio is larger than at SPS, but not baryon free at mid-rapidity at RHIC

(stat.) (sys.) (Event fraction)

p/p = 0.60 0.02 0.06 (top6%)

/(M.B. trig.) = 0.70 0.02 (top8%)

/(central trig.) = 0.72 0.04 (top15%)

- = 0.82 0.08 (top15%)

K+/K-(kink) = 1.17 0.07 (top15%)

K+/K-(dE/dx) = 1.14 0.01 0.06 (top6%)

K-/- = 0.15 0.02 (top6%)

p/- = 0.080 0.008 (top6%)

K*0/h- = 0.060 0.006 0.015 (top15%)

K*0h- = 0.058 0.006 0.015 (top15%)


sq sq +=

Chemical freeze-out model

Comparable particle ratios to experimental data

q: 1 for u and d, -1 for u and d q: lightquark chemical potential

s: 1 for s, -1 for s s: strangeness chemical potential

Particle densityof each particle

Decay all resonances

g : spi-isospin freedom


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


HBT


Particle correlations (HBT)

Size parametersTransverse and longitudinal direction

Duration time• From Rout and Rside

Phase space density• Combination of radius parameter and yield


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


3D analysis

Information:

• source size

• duration time (for transparent sources)

)(

)2()1(

)2,1(

21

222222

1),( LongLongSideSideOutOut RqRqRq

mixedNrealN

pPpP

ppPeppC ++−+=== λ

Pratt-Bertsch Parameterization (measured in the LCMS frame; (p1+ p2)z=0)

βτ 22SideOut RRÄ −=

p1

qOut

p2

qSide

x

y p1+p2


3 Dimensional - - HBT

Top 12% central events

0.125<pT<0.225 [GeV/c]

|y|<0.5

1D Projections of the 3D Pratt-Bertsch Parameterization

21.012.007.7

16.009.047.5

23.011.086.5

03.001.050.0

±±=±±=±±=±±=

Long

Side

Out

RRR

λ

qSide,qLong<20MeV/c qOut,qLong<20MeV/c

Systematic error result from the pair cuts (merging) and Coulomb correction

C(q

out)

C(q

Sid

e)

qout [GeV/c] qSide [GeV/c]

C(q

Long

)

qLong [GeV/c]

qOut,qSide<20MeV/c

[fm]

[fm]

[fm]

Coulomb corrected with a 5 fm source

No Coulomb correction

(sta.) (sys.)


Centrality dependence0.125 GeV/c < pT <0.225 GeV/c

tot: 32-72% 12-32% 0-12%

STAR Preliminary• ++, --, parameters similar

• λ`s don’t change with multiplicity• radii increase with multiplicity• roughly similar to AGS/SPS

Comparison with AGS/SPS • parameters roughly same • similar increase in ROut, RSide (geometric effect)

sys.error


mT dependence12 % most central events

0.125<pT<0.225 [GeV/c]

STAR Preliminary

0.225<pT<0.325 [GeV/c]0.325<pT<0.450 [GeV/c]

• ++, -- HBT parameters similarwith increasing mT

λ increases fewer resonances• radii decrease

position-momentum correlations

Comparison with AGS/SPS• parameters roughly similar to AGS/SPSWith increasing mT

• similar increase in λ• similar decrease of radii• stronger effect in ROut than at

AGS/SPS

2/)( 21TTT ppK +=

STAR

Preliminary

sys.error


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 anisotropyThe pressure gradient generates collective motion (aka flow)

Central collisions• radial flow

Peripheral collisions

• radial flow and anisotropic flow

Momentum spaceAlmond shape overlap region in coordinate space

ε =⟨y2 −x2⟩⟨y2 +x2⟩

x

z

y


Charged particle v2 versus centrality

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


Excitation function

WA98

NA49

h-


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


A Hydro view of the world

Hydro calculations: Huovinen, Kolb and Heinz


Charged particle anisotropy 0<pT<4.5 GeV/c

Only statistical errors

Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c


Conclusions

Net-baryon 0 at mid-rapidity! Anti-baryon/baryon ratios are toward 1, but still <1

Chemical Freeze-outTch ~ 200 GeV (150-200 MeV @ SPS,90-150 MeV @ AGS)

B ~ 50 MeV (200-270 MeV @ SPS,550-600 MeV @ AGS)

Large anisotropic flowHydro model can describe v2 an low pT (<2GeV/c)

Large v2 early thermalization

Thermal Freeze-outStrong space-momentum correlationsLarge radial flow ~ 0.6c (SPS/AGS <ß>= 0.4-0.5c)Tfo = 95-110 MeV (similar to SPS/AGS)

Masashi Kaneta, LBNL Masashi Kaneta for the STAR collaboration First results from STAR experiment at...

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