Helen CainesYale University

18th Winter Workshop on Nuclear Dynamics – Nassau, Bahamas Jan 2002

A Strange Perspective –

Spectra

If we knew what we were doing it would not be called research, would it? - A. Einstein

Helen Caines

Jan 2002

Spectra – What to look at

mt spectral shapes

Shape change as function of centrality

Species shape dependence

•Is there evidence of re-scattering?

•Enough to thermalise?

• If so for all centralities?

•Do particles freeze-out at the same temperature?

•Is there any dependence on centrality?

•How long does rescattering phase last?

•What about simpler systems? Compare to p+p

Short lived resonances

Helen Caines

Jan 2002

Particle identification

Approx. 10% of a central event

V0

K0

p

p

and by extension

K

Kink

K

a) dE/dxc) Topology

K p d

e

b) Resonances

Helen Caines

Jan 2002

Data Quality 1: Resonances

Mass and width are consistent with PDG book convoluted with TPC resolution

K*

K*_

STAR Preliminary

Helen Caines

Jan 2002

Data Quality 2: Peaks~0.84 /ev, ~ 0.61/ev

_

_ ~0.006 /ev, ~0.005/ev

~1.6 s/ev

6e-4 /ev , 6e-4~+/ev

Helen Caines

Jan 2002

Data Quality 3: Lifetime check

K0s

Lifetime : 8.03 ±0.05 (stat)cm

PDG Value : 7.89 cm

Lifetime : 2.64 ±0.01(stat)cm

PDG Value : 2.68 cm

Star PreliminaryStar Preliminary

Get pt shape of correction factors correct

Helen Caines

Jan 2002

Data quality 4: Kaon Comparison

STAR Preliminary

3 different methods with 3 drastically different efficiencies get same Slope and yield

Helen Caines

Jan 2002

Comparison of h- and , pT dist.

STAR Preliminary

Suggestive that the ratio baryons/mesons > 1 at high pT

Consequence of radial flow ?

or novel baryon dynamics ?Vitev and Gyulassy nucl-th/0104066

Helen Caines

Jan 2002

Kinetic Freeze-out and Radial Flow

If there is transverse flow

Look at mt = (pt2 + m2 )

distributionA thermal distribution gives a linear distribution

dN/dmt mte-(mt/T)

mt

1/m

t d2N

/dyd

mt

Slope = 1/T

Slope = 1/Tmeas

~ 1/(Tfo+ mo<vt>2)

Want to look at how energy distributed in system.

Look in transverse direction so not confused by longitudinal expansion

Helen Caines

Jan 2002

Mass dependence in p+p?

At lower energy (s=23 GeV) p+p collisions all particle species exhibit same inverse slope

Deviation of this behaviour in A+A attributed to flow

NA44-

Phys. Rev. Lett (78) 1997 2080

Helen Caines

Jan 2002

K0s m Spectra

Centrality % T (MeV)

0-5 289 ± 3 ± 17

5-10 291 ± 3 ± 17

10-20 286 ± 5 ± 17

20-35 278 ± 4 ± 17

35-75 269 ± 4 ± 16

Spectra well reproduced by an exponential

Helen Caines

Jan 2002

T=300-350 MeV

Note spectra are not feed-down corrected

mt Spectra

|y|<0.5

Centrality % T (MeV)

0-5 342 ± 9 ± 20

5-10 336 ± 9 ± 20

10-20 328 ± 7 ± 20

20-35 331 ± 8 ± 20

35-75 295 ± 7 ± 19

Fits are e(-mt/T)

See the same results (within errors) for

Spectra slightly better fit by a Boltzmann

Helen Caines

Jan 2002

Inverse slope for and

_

STAR Preliminary

0-14%

Helen Caines

Jan 2002

Mass dependence of mT slopes

Indication of strong radial flow at RHIC

Situation appears to be more complicated at RHIC than at the SPS

Note: inverse slope depends on the measured pT range(dE/dx p < 1 GeV/c)

1/m

T d

N/d

mT

(a.u

.)mT-m

STAR Preliminary

Multi-strange baryon seems to have early freeze-out

Helen Caines

Jan 2002

mT dist. from Hydrodynamic type model

)0 ,sinh ,(cosh )0,,( rezrtu

tanh 1r )( rfsr R

s

Ref. : E.Schnedermann et al, PRC48 (1993) 2462

flow profile selected

(r =s (r/Rmax)0.5)mmT

1/m

T d

N/d

mT

(a.u

.)

K

p

Helen Caines

Jan 2002

explosive radial expansion at RHIC high pressure

ßr (RHIC) = 0.52c Tfo (RHIC) = 0.13 GeV

K-p

-

<r > [c]

Tth [

GeV

]

0 0.40 0.4<r > [c]

Tth [

GeV

]

Fits to the hydro. model

mT - m [GeV/c2]

1/m

T d

N/d

mT

(a

.u.)

-

K-

p

solid : used for fit

STAR Preliminary

Helen Caines

Jan 2002

Tth and <r> systematic

• <r>– saturates around AGS

energy– increased at RHIC?

• Tth– saturates around AGS

energy

STA

R

PHE

NIX

Tth

[GeV

]<

r>

[c]

Picture for central collisions - lots of rescattering and flow

Helen Caines

Jan 2002

mT slopes vs. Centrality

Common T at most peripheral collisions?

Helen Caines

Jan 2002

mt in p+p at high s

Dumitru, Spieles –Phy. Lett. B 446 1999

NOT flow as Hydro calc. shows.

Pythia –Confirmed by UA1/5 experiments at 540 GeVshows strong mass dependence

Due to mini jets – create

colour strings that are not ONLY

longitudinal.

Want to look in more detail at 200 GeV

More complicated picture at high s – How to disentangle

Helen Caines

Jan 2002

p+p, STAR and Strangeness

Data is from ~1/10th of that taken

Should get nice spectra

Helen Caines

Jan 2002

How long does rescattering last?

10 100 s GeV

From spin counting

K*/K = vector mes/mes

= V/(V+P)

= 0.75

See lower ratio at RHIC than in elementary collisions

Due to re-scattering of daughters?

Helen Caines

Jan 2002

K* Slope

STAR Preliminary

MT-M0 (GeV/c2)

Statistical error only

Central events

(top 14%)

K*0

T ~ 400 MeV

Similar to that of and (same mass)

No evidence of a low pt

suppression

Must be short time scale from chemical freeze-out to thermal

OR long lifetime with lots of regeneration.

Helen Caines

Jan 2002

Getting the time scale and temp

G. Torrieri and J. Rafelski, hep-ph/0103149

Can be hot and long lived or cooler and short timescales to get same ratio.

Measure more than one resonance and can pin down T and t

Helen Caines

Jan 2002

What to look at - Conclusion

mt suggest thermalization has

occurred

Flow decreases with decreasing centrality

Yes but with a large flow. Not seen as strongly by

strange particles

•Is there evidence of re-scattering?

•Enough to thermalise?

• If so for all centralities?

•Do particles freeze-out at the same temperature?

•Is there any dependence on centrality?

•How long does re-scattering phase last?

•What about simpler systems?

comparison to p+p data harder at this

energy

Elastic re-scattering phase short

Helen Caines

Jan 2002

The STAR CollaborationRussia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino

U.S. Labs:ArgonneBerkeleyBrookhaven

U.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinWashington UniversityWayne State UniversityYale University

Brazil: Universidade de Sao Paolo

China: IHEP - BeijingIPP - Wuhan

England: University of Birmingham

France:IReS StrasbourgSUBATECH - Nantes

Germany: MPI – MunichUniversity of Frankfurt

India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - Bombay

Poland:Warsaw University of Technology