Helen Caines Yale University Alice Week - Erice– Dec. 2005 An overview of recent STAR results What have we learnt this past year?

Helen CainesYale University

Alice Week - Erice– Dec. 2005

An overview of recent STAR resultsWhat have we learnt this past year?

Helen Caines Alice Week - Erice – Dec. 2005 2

Run Year Species √s [GeV ] Ldt

01 2000 Au+Au 130 1 b-1

02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1

03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1

04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1

05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1

The data



short

liv

ed

reso

nance

s

Tch

s

STAR white paperNucl Phys A757 (05) 102

•Tch ≈ TC ≈ 165 ± 10 MeVChemical freezeout ≈ hadronization.•s ~ u, d Strangeness is chemically equilibrated.

Chemical freeze-out


Lifetime and size

resonance decays and regeneration: measure kinetic freezeout – life time.

Re-scattering and regeneration needed! Finite time span from Tch to Tfo

Npart

HBT: measures freeze-out source sizes (marked by collective flow).

HBT size (low kT): x2 expansioninitial final in Au+Au.What is the size at chemical freeze-out? may be assessed via - correlations.


• p,K, p <T> 200 GeV > 62 GeV Tkin 200 GeV = 62

GeV

• <T> 200 GeV = 62 GeV Tkin 200 GeV > 62

GeV

Radial Flow

Tkinetic from a Blast-Wave is not same as the Temperature from a Hydro Model.

• Temperature Tkinetic is higher for baryons with higher strange quark content for Blast-wave fits.

• Spectral shapes are different.

Most Central Collisions

0.13

T=100 MeV

T=132 MeV


Baryon/Meson ratios

Au+Au 0-10%

p+p

Baryon stopping has strong effect

Shape driven by flow?


Elliptic flow

Almond shape overlap region in coordinate space

Anisotropy in momentum space

Interactions/ Rescattering

dN/d ~ 1+2 v2(pT)cos(2) + …. = atan(py/px) v2 = cos2

v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane

P. Kolb, J. Sollfrank, and U. HeinzAu+Au at b=7 fm

Equal energy density lines

Elliptic flow observable sensitive to early evolution of system

Mechanism is self-quenching

Large v2 is an indication of early thermalization


Elliptic flow v2H

ydro

by H

uovin

en e

t al.

hydro

tuned t

o fi

t ce

ntr

al

spect

ra d

ata

.

PRC 72 (05) 014904

200 GeV Au+Aumin-bias

large v2 (even ): strong interactions at early stage

large v2 of (low hadronic x-sections): partonic collectivity at RHIC.

First time hydro works: suggests

early thermalization - = 0.6 fm/c = 20 GeV/fm3

Soft (QGP) EOS favored:

sub-hadronic DOF.


• Significantly smaller v2 in Cu-Cu than in Au-Au for given centrality• Scales with v2(Npart)• Large non-flow effects at high pT

v2 – Cu-Cu vs Au-Au

Greater non-flow effects in Cu-Cu.


solid: STARopen: PHENIX PRL91(03)

The complicated observed flow pattern in v2(pT) for hadrons

is predicted to be simple at the quark level underpT → pT /n

v2 → v2 / n ,

n = (2, 3) for (meson, baryon)

Works for p, (, K0s, , ,

v2s ~ v2

u,d ~ 7%

)2cos( )( 21 2

2

T

T

pvddp

Nd

Au+Au √sNN=62 GeV

STAR Preliminary

Constituent quark scaling

Constituent quark DOF – deconfinement?


• s-Baryon production is ~constant at mid-rapidity.

STAR Preliminary

s-Baryon rises smoothly at mid-rapidity.

Au+Au

Pb+Pb

Collision energy dependencies

What determines the overall yields?

STAR Preliminary


Strangeness enhancement

Correlation volume:

V= ANN·V0

ANN = Npart/2 V0 = 4/3·R0

3

R0 = 1.1 fm proton radius/strong interactions

T= 170-177 MeV = 1

K. Redlich – private communication

Particle ratios indicate T= 165 MeV

= 1/3 fits best, very sensitive to T

STAR Preliminary Solid – STAROpen – NA57

STAR Preliminary


Flavor dependence of scalings

Binary scaling for heavy flavor quark hadrons

PHENIX D’s

Participant scaling for light quark hadrons

Hadrons with strange quarks an add-mixture of Npart and Nbin?


Motivation from h-

N.B.: SPS energy only 17 GeV

There’s a correlation between dNch/d and Npart/2

If know npp can predict yield at any Npart

small dotted lines are:

dNch/dnpp(1-x)Npart/2 + xNbin

npp= Yield in pp

= 2.29 ( 1.27)

x = 0.13

PHOBOS: Phys. Rev. C70,

021902(R) (2004)


Strangeness and dNch/d

SPS and RHIC data follows same curves as a func. of dNch/dη

dNch/dη - strongly correlated to the entropy of the system!

Look at yields relative to pp

Entropy alone seems to drive much of the soft physics

HBT radii show similar scaling with dNch/dη


High pT suppression

J. Adams et al, Phys. Rev. Lett. 91 (2003) 072304

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

Binary coll. scaling p+p reference

♦ Central Au+Au collisions: factor ~4-5 suppression. ♦ pT >5 GeV/c: suppression ~ independent of pT.♦ pQCD describes data only when energy loss included.

RAA << 1; RdAu > 1 Confirms final state effects present


Photons - unsuppressedHadrons - suppressed

Sur

viva

l Pro

babi

lity

Direct

0,

Confirming the probe

We have an understood and calibrated probe


Geometrical dependence of RAA

• RAA scales smoothly from Au+Au Cu+Cu p+p

Scaling prefers Npart1/3, though Npart

2/3 not strongly excluded


Nuclear modification factors - RCP

√sNN=200 GeV

√sNN=62 GeV 0-5%

40-60%

0-5%

40-60%

NA57, PLB in print, nucl-ex/0507012

√sNN=17.3 GeV

First time differences between and

B absorption?

Recombination or different “Cronin” for and K at SPS?


Nuclear modification factors - RAA

HIJING/BBar + KT ~ 1 GeVStrong Colour Fieldqualitatively describes RAA.

SCF - long range coherent fields

SCF behaviour mimicked by doubling the effective string tension

SCF controlsqq and qqqqproduction rates and s

Topor Pop et al. hep-ph/0505210

Effects dominate out to high pT

SCF only produced in nucleus-nucleus collisions RAA≠ RCP


Dead cone effect

• Coupling of heavy quarks to the medium reduced due to mass

Djordjevic et al, nucl-th/0507019

See also Armesto et al, Phys. Rev. D71 (2005) 054027

Expectation: Little suppression for single e- from heavy flavor


Non-photonic e- RAA

In central Au+Au collisions, non-photonic electrons are very strongly suppressed at high pT

•Data agree with c e predictions if the density is quite high•But b e should be there, too

–Is our understanding of c and b production correct?–Is our understanding of partonic energy loss correct?–How strong are the in-medium interactions?–How dense is the medium?

Re-scattering significant?


Alternative scenario: collisional contribution

AMPT:(C.M. Ko)

← σ=10 mb← σ=3 mb

← pQCD

Moore & Teaney, hep-ph/0412346

Large collisional interactions also produce suppression but also v2

v2 signal in e-


Jet correlations in proton-proton reactions.

Strong back-to-back peaks.

Jet correlations in central Gold-Gold.

Away side jet disappears for particles pT > 2 GeV

Jet correlations in central Gold-Gold.

Away side jet reappears for particles pT>200 MeV

Azimuthal Angular Correlations

Jet quenching


Three regions on away side:center = (, ) ±0.4corner = (+1,+1) ±0.4 x2cone = (+1,-1) ±0.4 x2

away

near

Medium

mach cone

Mediumaway

near

deflected jets1

2

0

0

1

2

0

0

pTtrig=3-4, pT

assoc=1-2 GeV/c2-particle corr, bg, v2 subtracted

φ2=

φ2-φ

trig

d+Au min-bias

dN

2/d

Δφ

1dΔ

φ2/N

trig

φ1=φ1-φtrig

φ2=

φ2-φ

trig

Au+Au 10%

difference in Au+Auaverage signal per

radian2:center – corner = 0.3 ± 0.3 (stat) ± 0.4

(syst)center – cone = 2.6 ± 0.3 (stat) ± 0.8

(syst)

conical flow? 3-particle correlation

d+Au and Au+Auelongated along diagonal: kT effect, and deflected jets?

Distinctive features of conical flow are not seen in present data.


Emergence of dijets

For the first time: clear jet-like peaks seen on near and away side in central Au-Au collisions

8 < pT(trig) < 15 GeV/c

STAR Preliminary

pT(assoc)>6 GeV

No background subtraction!


Centrality dependence of yields

• Near-side yields consistent within errors

• Away-side yields decrease monotically with increasing NPart

– Suppression pattern similar for two pT(assoc) ranges!

Fit scaledby x2

8 < pT(trig) < 15 GeV/c

IAA ≈ RAA ≈ 0.20-0.25

≈ 5-7 GeV2/fm in central Au+Au @ RHICq̂

IAA = Yield (AA)/ Yield(dAu)


mT scaling

STAR Preliminaryp+p 200 GeV

No complete mT scaling

Au-Au

Radial flow prevents scaling at low mT

Seems to scale at higher mT

p-p

Appears to be scaling at low mT

Baryon/meson splitting at higher mT – Gluon jets?


Gluon vs quark jets in p-p

Quark jets events display mass splitting

Gluon jets events display baryon/meson splitting

No absolute mT scaling – “data” scaled to match at mT~1 GeV/c

Way to explore quark vs gluon dominance


STAR Preliminary

Changing the probe: towards -jet

• Correlations triggered on : clear near and away-side peaks • Strong contamination remains from 0 decay daughters

– Work in progress to separate out direct

• does not couple to medium or fragment into jets– remove trigger surface bias and fragmentation uncertainty in Q2


We have successfully createdthe Quark Gluon Plasma!

Now we have many exciting properties that we are just beginning to explore….• low viscosity• rapid equilibration• novel hadron formation mechanisms• jet quenching and medium reaction• temperature determination• degrees of freedom

Conclusions


The STARSTAR Collaboration

U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs

U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale

Brazil: Universidade de Sao Paolo

China: IHEP - Beijing, IPP - Wuhan, USTC,Tsinghua, SINAP, IMP Lanzhou

Croatia: Zagreb University

Czech Republic: Nuclear Physics Institute

England:University of Birmingham

France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes

Germany: Max Planck Institute – Munich University of Frankfurt

India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC

Netherlands:NIKHEF/Utrecht

Poland:Warsaw University of Technology

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

South Korea:Pusan National University

Switzerland:University of Bern

STARSTAR

Documents

Helen Caines Yale University Alice Week - Erice– Dec. 2005 An overview of recent STAR results What have we learnt this past year?