Helen CainesYale University

March 2003

An Update from STAR –

Using Strangeness to Probe Collisions

You are never too old to set another goal or to dream a new dream

C.S.Lewis 1898-1963

Helen Caines

SQM – March 2003 2

Outline

Soft - Bulk of the production- v2 flow - Charged hadrons, , K- Chemical freeze-out – Strangeness enhancement?- Rescattering – K*,(1520)- Thermal Freeze-out – different behaviour?- Radii – K0

s HBTHard – Early times

- Quark vs Gluon production – p/p and - High pt suppression – charged hadron vs K0

s vs p-p

- <pt> - Mini jets?

Outlook – Look out for at QM2004- Comparison p-p data – Relative rates- d-Au – Cold vs hot nuclear matter - FTPC - at high y

Strange Particles the Ultimate Probes!

Helen Caines

SQM – March 2003 3

STAR Strange Spectra @ 200 GeV

STAR Prelimin

ary

STAR Prelimin

ary

K

K*

STAR Preliminary

preliminary

preliminary

K0s

Preliminary

STAR Preliminary

Helen Caines

SQM – March 2003 4installation in 2003

Endcap Calorimeter

Year 2000,

The STAR Detector (Year-by-Year)

ZCal

Time Projection Chamber

Magnet

Coils

RICH * yr.1 SVT ladder

TPC Endcap & MWPC

ZCal

Central Trigger Barrel

FTPCs

Silicon Vertex Tracker *

Vertex Position Detectors

year 2001,

+ TOF patch

Barrel EM Calorimeter

year-by-year until 2003,

Helen Caines

SQM – March 2003 5

130 GeV Data

STAR Preliminary

All strange particles seem to increase linearly with h-

No step functions, no big surprises

Helen Caines

SQM – March 2003 6

Improvements with 200 GeV Data

+K+

STAR Preliminary

Finer centrality binning

18%

ex

trap

olat

ion

STAR Preliminary

Better stats. and measurements

STAR Preliminary

+

STAR Preliminary

Much higher reach in pt

Helen Caines

SQM – March 2003 7

B/B Ratios

Au+Au

STAR preliminary

All data:• mid-rapidity• ratios from raw yields

Talk: Anja Billmeier,

Fri

STAR p+p √s = 200 GeV

Similar net baryon densities in all 3 collision data

Helen Caines

SQM – March 2003 8

Statistical models

As we know beautiful agreement between models and data

Helen Caines

SQM – March 2003 9

Centrality Systematics of Chemistry

Appears to be a saturation of strangeness

Helen Caines

SQM – March 2003 10

Statistical models

What about the

resonances?!?

As we know beautiful agreement between models and data

Helen Caines

SQM – March 2003 11

Resonances and Survival Probability

Chemical freeze-out

Kinetic freeze-out

lost

measured

K

K* K

K*

K*

K

K*

K Kmeasured

• Initial yield established at chemical freeze-out

• Decays in fireball mean daughter tracks can rescatter destroying part of signal

• Rescattering also causes regeneration which partially compensates

• Ratio to “stable” particle reveals information on behaviour and timescale between chemical and kinetic freeze-out

time

Need more than one resonance

Two effects compete – Dominance depends on decay products and lifetime

Helen Caines

SQM – March 2003 12

Resonance Ratios

Talks: Patricia Fachini, Ludovic Gaudichet & Haibin Zhang, Sun.

(1520) ->pK (13 fm/c)K* -> K ( 4 fm/c)-> (1.3 fm/c)

UrQMD: signal loss K*(892) (1520)

SPS (17 GeV) [1] 66% 50%

RHIC (200GeV) [2] 55% 30%

STAR PreliminaryAu-Au and p-p√s=200GeV

Helen Caines

SQM – March 2003 13

Hydro-dynamically motivated fit

mT - m0 (GeV)

1/m

T d

N/d

mT

(a

.u.)

STAR Preliminary

tanh 1 r

R

sE.Schnedermann et al, PRC48 (1993) 2462

-

K-

p

solid : used in fit

dn

mT dmT r dr mT K1

mT coshT

0

R

I0pT sinh T

Shape of the mT spectrum depends on particle mass

where

r =s (r/R)n

Multiple interactions lead to thermalization -> limiting behaviour ideal hydrodynamic flow

Two Parameters: T and

Helen Caines

SQM – March 2003 14

,K,P,

Thermal freeze-out at 130 GeV

• , K, P, : Common thermal freeze-out at T~100MeV and <>~0.52c

Assume r= s(r/R)

Tfo - (), 1 and 2 contours

Talk: Javier Castillo, Mon

,K,P,

, (?): Show different thermal freeze-out behaviour:

Early freeze-out due to smaller cross-section ?Radial flow developing at early times?

STAR Preliminary

Helen Caines

SQM – March 2003 15

<pt> vs Centrality

, K, p - <pt> increase

with centrality

- Heavy mass increase faster

All consistent with radial flow

Talk: Jinguo Ma, Sun

seems to flow differently – Early freeze-out too?

Helen Caines

SQM – March 2003 16

Elliptic Flow and the Hydro limit

• Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric)

• Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp)

y

x

py

px

coordinate space

Momentum space

12 , tan ( )cos 2( ) y

xrv

p

p

3 2

31

11 2 cos

2 n rnt t

d N d NE v nd p p dp dy

High v2 evidence of early thermalization

Zhang, Gyulassy, Ko, PL B455 (1999) 45

Helen Caines

SQM – March 2003 17

Strange particle v2 at low pt

Mass dependence well described by blastwave model modified to allow for an azimuthal modulation of the second harmonic to the transverse rapidity:= 0 +acos(2) and a variation in the azimuthal density: s2.

1

STAR PreliminaryAu-Au 200 GeV

V2

Also seen at 130 GeV 2002, Phys. Rev. Lett. (2002) 132301-1

Combined fit to K0s and gives

Tfo ~ 100 MeV0 ~ 0.66 a ~ 0.04s2 ~ 0.04In good agreement with mt spectra

Pt GeV/C

Do and agree?

Helen Caines

SQM – March 2003 18

X 10

K0sK0

s Correlations

)exp(1),( 22qRqPC Fit to a gaussian

K0s

= 0.5 0.1 Rinv = 5.8 0.7

C2

STAR Pre

limin

ary\

Talk: Selemon Bekele, Thurs

M (GeV/C2)

Enough K0s/event to perform

HBT measurement

Helen Caines

SQM – March 2003 19

HBT vs mt

Rinv for K0s does not

seem to obey same mt scaling

Need more detailed studies before conclusive statement made

Wiedemann and Heinz expect:

to drop with 1/ma

t

due to collective flow.

3/1VRHBT

(a ~ 0.5)

Helen Caines

SQM – March 2003 20

Observing Hadronization Timescale

The Premise:• Charge/anti-charge pairs are created close in space-time• Early creation (hadron gas)

• Longitudinal expansion and rescattering pulls pairs apart– Loose correlation in rapidity

• Late creation (after deconfined phase?)• Pairs only form at hadronization, late in collision• Less rescattering

– Less loss of correlation in rapidity

STAR Preliminary Kaons 200 GeV Au-Au

Balance function tries to measure this correlationWidth of balance function then related to time between hadronization and freeze-out

Helen Caines

SQM – March 2003 21

Balance Function at 200 GeV

Talk: Gary Westfall, Fri

Narrower widths for more central data: Delayed hadronziation?

STAR Preliminary

Smooth transition from p-p to Au-Au

K narrower than just mass effect?)

Helen Caines

SQM – March 2003 22

Summary of Low pt Observations

– Particle production is large • Small change from 130 to 200 GeV

– Vanishing anti-baryon/baryon ratio (0.7-0.8)• close to net baryon-free but not quite, ~same for 130, 200 and pp

– Particles ratios suggest chemical equilibrium

• Tch170 MeV, b<50 MeV near lattice phase boundary

– Resonances appear strongly affected by rescattering in medium• Rescattering and regeneration compete

– System exhibits collective behavior (radial + elliptic flow) • strong internal pressure that builds up very early• Some particles appear to freeze-out at earlier times

– The system appears to hadronize late• Balance function results

– Large system at freeze-out • K0

s appear to break mt scaling

Overall picture: system appears to be in equilibrium, but it explodes and hadronizes rapidly

Need more Au-Au data to get clearer picture

Helen Caines

SQM – March 2003 23

Strange Particles at High pt

Change in shape at higher pt.

preliminary preliminary

Helen Caines

SQM – March 2003 24

“Soft” vs “Hard” Physics

Npart: Number of participants number of incoming nucleons (participants) in the overlap region

“Soft” Physics -

“Hard” Physics - Nbin: Number of binary collisions number of equivalent inelastic nucleon-nucleon collisions

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbin>/inelp+p

N-N cross section

Nuclear Modification Factor:

If no “effects”: R < 1 in regime of soft physics R = 1 at high-pt where hard scattering dominates

Helen Caines

SQM – March 2003 25

A significant difference is seen between the pt dependence of K0

S and Λ RAA.

Identified Particle Measurements

preliminary

preliminary Talk: Hui Long, Thurs

For pt from 1.8-3.2 GeV/c in central collisions Λ production approximately follows Nbin scaling.

At higher pt however, a suppression with respect to Nbin scaling is seen for both – “standard” fragmentation?

Baryon/Meson difference or merely mass?

Helen Caines

SQM – March 2003 26

preliminary

preliminary

Minimum bias v2

Talk: Paul Sorensen,Thurs

At high pt Hydro-likebehaviour stops

Deviation occurs earlierFor K0

s than for

Again mass or baryon/meson dependence?

Au-Au 200 GeV

Helen Caines

SQM – March 2003 27

Interplay of soft and hard processes

Hydrodynamics plus jet quenching describes general form of v2 pt dependence

Moderate pt

- pion dominated by quenched pQCD,

- baryon production dominated by non pQCD effects (e.g.baryon junctions or hydro) expect qualitative different v2 behaviour for different particle species

GLV theory

Does it explain RAA?

Helen Caines

SQM – March 2003 28

Recombination vs Fragmentation

Bass et al., nucl-th/0301087Also S. Voloshin QM2002

Lower pt

-Recombination dominates High pt - Fragmentation dominates

Intermediate pt - Two processes compete

Recombination dominates out to higher pt for baryons (3 q)

- hadron suppression due to parton energy loss dominates later

RAA different for mesons and baryons,What about v2 ?

Helen Caines

SQM – March 2003 29

B/B ratio at High Pt

Talk: Ben Norman, Thurs

Both Ratios fall at High pt

Seeing difference in quark vs gluon production mechanisms?

Helen Caines

SQM – March 2003 30

Summary of High pt Observations

•Strong hadronic suppression •Onset at different times for different species

• Azimuthal anisotropy at high pt

Plateau occurs at different times for different species

• Suppression of back-to-back hadron pairs (Not shown here) large parton energy loss and surface emission?

Need d-Au

disentangle initial state effects in jet production (shadowing, Cronin enhancement)

resolution of jet quenching picture J/ and open charm: direct signature of deconfinement?

Helen Caines

SQM – March 2003 31

<pt> and p-p collisions

Talk: Richard Witt, Thurs

K0s

Power Law fits

STAR Preliminaryp-p 200 GeV

STAR Preliminaryp+p @s = 200 GeV

STAR Preliminaryp-p 200 GeV

K0s

Not flow in p-p so evidence for mini-jets?

Helen Caines

SQM – March 2003 32

K0s

News from the front - Latest d-Au update

STAR running since January

√s = 200 GeV

already > 40M events taken!

Varying Number of events in each plot, NO PHYSICS!!!!But there will be..

Helen Caines

SQM – March 2003 33

High Rapidity s?

Results from ~ 2 M dAu minbias events

FTPC west only (d side)

First hint of signal in d-Au at forward rapidity

Not only use the FTPC’s for multiplicity at high y

Helen Caines

SQM – March 2003 34

B(arrel)EMC

• dAu run (January 2003)– 60 modules

instrumented– (, ) ~ (1.0, 2p)– 2400 towers

Physics with the BEMC• Et

• 0

0 d-Au

• High-pt trigger x100 enhancement at 5 GeV

•Jet and Quarkonia TriggerUnder

commisioning

Poster – Manual CalderonThorsten Kollegger

Helen Caines

SQM – March 2003 35

Russia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino

U.S. Laboratories: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 Paulo

China: IHEP – BeijingIMP - LanzouIPP – WuhanUSTCSINR – ShanghaiTsinghua University

Great Britain: University of Birmingham

France:IReS StrasbourgSUBATECH - Nantes

Germany: MPI – MunichUniversity of Frankfurt

India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC – Kolcata

Poland:Warsaw University of Tech.

more than 450 collaborators, 46 institutions, 9 countriesMany here today:

Talks:Selemon Bekele – Kaon HBT

Anja Billmeier – Strange particle ratios in p-pJavier Castillo – Multi-strange baryons and thermal

freeze-outPatricia Fachini – and f0 production

Ludovic Gaudichet – (1520) production Hui Long – Suppression of high pt strange hadrons

Jinguo Ma – f productionBen Norman – Ratios as function pt and centralityPaul Sorensen – K0

s and Azimuthal AnisotropyGary Westfall – Balance functions

Richard Witt – Strange particle spectra in p-pHaibin Zhang – K* production

Posters:John Adams – reconstruction

Manuel Calderon de la Barca Sanchez – J/ triggeringMagali Estienne – reconstruction

Julien Faivre – Improving reconstruction with LDA methods?

Mark Heinz – K0s reconstruction

Thorsten Kollegger – Heavy flavour reconstructionSevil Salur – * reconstruction

The STAR Collaboration