What Happened in China ?

Gluons can begin to fuse with high enough gluon density. Saturation will limit parton production

Final state charged particle yields per collision limited?

Gluon Saturation?

Gluon Saturation does not appear to set in for peripheral collisions Cannot yet rule out Eskola’s saturation for central collisions Kharzeev’s initial-state saturation picture is consistent with data

Eskola, Kajantie, and Tuominen: hep-ph/0009246Kharzeev, Nandi: nucl-th/0012025

r/gggPhys. Rev. Lett. 86, 3500 (2001)

Energy density

02j

TB

dE

R

1

c dy

1

Bjorken formula for energy density in terms of measured transverse energy assuming a thermalized system at time

PHENIX: Central Au-Au yields

6.88 fm(hard sphere radius)

Time to thermalize the system (~ 1.0 - 0.2 fm/c?)

Phys. Rev. Lett. 87, 52301 (2001)

2%

26T39

y 0

dE578 GeV 1.19 0.01

dy

Is the energy density high enough?The PHENIX EMCal measures transverse energy

For the most central events:Bjorken~ 4.6-23 GeV/fm3

critical~ 0.6-1.8 GeV/fm3

Lattice phase transition:

Energy deposition is certainly adequate, but does it create a thermalized new phase of matter while crit?

Roughly 1.5 to 2 times higher than previous experiments if assume same formation time

Latticec

Bj~ 4.6 GeV/fm3

J. Nagle

Bj~ 23.0 GeV/fm3

thermalization time?

Comparison with pp baselineCentral

Peripheral

Peripheral

consistent with NN scaled by number of collisions

Central

below scaled NN spectrum

larger deficit than unidentified hadrons

Scaled NN

ratio’s with pp and peripheralcentral binary central

AApp

/Yield NR

Yield

central binary central

peripheral binary peripheral

/

/

Yield N

Yield N

h

h

AAR

Cen

tral

/per

iph

eral

PT PT

00

Complications• “Ordinary” Nuclear effects:

Cronin Effect and PT broadening Nuclear shadowing of gluon structure functions

Issues:Does the parton fragment inside the medium?Particle composition is a strong function of pT

Other unknown effects?

q

q

Year-1 High PT ConclusionsCentral collision data shows significant suppression relative to prediction without energy loss.

Indicates a novel effect: Indicates a novel effect: deviation from point like deviation from point like scalingscaling

It is consistent with parton energy loss , but too early to make definitive conclusion.A systematic study including pA and higher PT reach is needed. Stay tuned …

“Other” Year-1 PHENIX results

HBT

Electrons

Gamma Distribution Calculation

Centrality:

0-5%

PHENIX Preliminary

<Pt> (GeV/c)

Fluctuations

5.9 0.47.9 1.1 6.2 .5

= 0.49 .07

Elliptic Flow

PHENIX PreliminaryPHENIX Preliminary

BRAHMS acceptance 00 & 01

FFS

BFS

• N=dE /<dE>• P(0)/P(n1)• Background corr.due to

secondaries (37-50%)• Consistency between 4

independent. detector systems

• 65 AGeV+65 AGeV: N(ch)d= 4050±300• Central 0-5% dN(ch)/d (=0) =550• FWHM of distribution

= 7.6 0.7

0-5%

10-20%

20-30%

30-40%

40-50%

5-10%

600

BRAHMS Subm. Phys. Lett. B 7/2001.

Charged Particle Mult. at 130 GeV

BRAHMS. Subm. Phys Lett. B. 2001

SPS

dNch/d for100 AGeV+ 100 AGeV

• 100 AGeV + 100 AGeV AU+AU

N(ch)d= 5100±300• Central 0-6% dN(ch)/d (=0) =61050• FWHM of distribution = 7.9 1.0

BRAHMS 200AGEV

Hard and Soft vs.High Density QCD @ 200 AGeV

• Kharzeev and Levin (nucl-th/0108006)

• Soft-Hard:

dN/d=(1-X) npp <Npart>/2

+ X npp <Ncoll>

<Ncoll>=1049, <Npart>=339, npp=2.43 =>dN/d=668 (with X=0.9)

• High Density QCD-saturation:

dN/dy =

f( Npart, Qs2, ,QCD,s,y)

with =0.3 from HERA data

=> dN/d=620

(using dN/d=549 at s=130GeV)

(

(

(

)

)

)

Total production of charged particles

• 130 AGeV• 4000 charged part. observed• Nch 23.5 pr. part. pair• cf. Nch 17 in p+p at s=130GeV

• 35-40% increase over p+p

Syst

BRAHMS

200 AGeV

200 AGeV 5100 charged part.

observed Nch 30 pr. part. pair cf. Nch 20 in p+p at

s=200GeV 50% increase over p+p

Bjorken limit reached for Au+Au s= 130AGeV?

ISR R803

s=23

s=63

BRAHMS

PRL sept. 2001

p-bar/p ratio:Centrality dependence

BRAHMS 2k

How consistent are the models?

Summary

RESULTS: 100+100

• Nch (0-5%) 5100

• dN/d (y=0) 625. FWHM 7.8

• N(ch) 30 pr. participant-pair

• dN/d (y=0) 3.6 pr. part. Pair

• p-pbar/p 0.48±0.05 (y=2)

0.99±0.01(stat) (y=3)

RESULTS: 65+65• Nch (0-5%) 4000• dN/d (y=0) 550. FWHM 7.6• N(ch) 23 pr. participant-pair• dN/d (y=0) 3 pr. part. Pair

• AntiMeson/Meson close to unity

• p-bar/ p vs y shows increased but still incomplete transparency

• Midrapidity Plateau?• y =0,0.7,2 : pbar/p 0.64, 0.66, 0.41

(±0.05 ± 0.06)• Weak pt and centrality dependence• Bjorken limit not reached• Models inconsistent with data

Energy Dependence at =0Errors are dominated by systematics

AGS/SPS points extracted by measured dN/dy and <mT>

New data at 200 GeV shows a continuous logarithmic rise at midrapidity

fpp(s) =

Ratio of dN/d at 200 & 130 GeV 90% Confidence Level

Pseudo-rapidity Distributions• Using Octagon and Ring

subdetectors• Measure out to ||<5.4• Corrections

– Acceptance– Occupancy– Backgrounds (from MC)

• Systematic errors– 10% near =0– Higher near rings

Back

grou

nd C

orr.

HIJING Simulation

PRL 87 (2001) forthcoming

Centrality Dependence vs.

• Total charged multiplicity is about 4200 ± 420 for central events

• At high 3-4 multiplicity starts to decrease as a function of Npart

• Similar feature seen in pA collisions

PRL 87 (2001) forthcoming

Comparison to pp and models

Peripheral

Central

Scaled UA5 data

HIJINGAMPT

(rescattering)

Ybeam

(Y130/Y200)dN/d = fpp(s)

PRL 87 (2001) forthcoming

DeMarzo et al, 1984

Systematic error not shown

Change in dN/d with energy

• UA5 looked for ‘limiting fragmentation’ by plotting dN/d with - Ybeam

• We can do the same thing with the PHOBOS data– agreement for AA in the fragmentation region

200 GeV

130 GeV

UA5 200 GeV(NSD)

UA5, Z.Phys.C33, 1 (1986)

Saturation model fits to 130 Data

m2=2Qsm, pT=Qs, ~.3 extracted from HERA F2 data

Kharzeev & Levin, nucl-th/0108006, input from Golec-Biernat & Wüsthoff (1999)

42/

2

2

2

222

11

ln

sinh

cosh

ys

QCD

ysy

opart

TT

es

Qy

eQe

s

scN

ypm

y

d

dN

Azimuthal Asymmetry at =0

• 130 GeV data from PHOBOS • Correct for occupancy, resolution

of reaction plane estimate• Good agreement with hydro

calcuations for central events (and STAR…)

• X = cos(ni), Y = sin(ni) n = atan(Y/X) v2 = <cos 2(2)>

• At midrapidity, using “SymOct”• Account for detector response

using “weighting matrix”.

Padsin

Pads in z

Asymmetry vs. Multiplicity

• Compare– Flow for mid-central

events – Multiplicity per participant

pair for central events (only 10% variation down to Npart=100)

• Flow (for more peripheral events) seems to scale with particle density

• 200 GeV data should be interesting!– Saturation or scaling?

PRELIMINARY

Asymmetry vs. Rapidity

Systematic Error ~ .007

Preliminary Results – final results coming soon!

dy dp p

dN

p m

p

d dp p

dN

T T T

T

T T2 2

) cosh (

cosh

P. Kolb, Utah proc.

Results on particle ratios

• Measured near midrapidity – 0 < y <1 (species-dependent)

• Final results submitted to PRL (Apr. 2001)

• Consistent within systematic errors with results presented at QM2001 (Jan. 2001)

• Smaller systematic errors (10% 6%)

.)(06.0.)(04.060.0

.)(06.0.)(07.091.0

.)(02.0.)(01.000.1

syststat

syststat

syststat

p

p

K

K

Conclusions

• Systematics of charged particle production have been explored by the PHOBOS experiment– Energy – multiplicity rises approximately logarithmically– Centrality – data shows simple interpolation between pp and central AA– Rapidity – scaling with Npart changes in fragmentation region – Azimuthal – elliptic flow appears to scale with multiplicity– Particle ratios are reaching zero net baryon number, small B

• Broad features of particle production are consistent with soft nature of strong interactions– pp and pA collisions are very instructive

• Theoretical models are assimilating new data– None simultaneously describe full set of systematics!

Energy dependence of v2

Logarithmic rise

Statistical models• Braun-Munzinger et al. (hep-ph/0106066)

- Follows curve for <E>/<N> = 1 GeV at freezeout

- Usesphenomenologicalparameterization:

B(s)1.27 GeV

(1 s /(4.3 GeV)) J. Cleymans & K. Redlich,PRL 81 (1998) 5284

Strangeness production

Lines of constant S where:

<E>/<N> = 1 GeV

I. Increase instrange/non-strangeparticle ratios

II. Maximum isreached

III. Ratios decrease(Strange baryonsaffected more stronglythan strange mesons)Braun-Munzinger et al.

hep-ph/0106066

Implications for ratios

s (GeV)

(PRELIMINARY)

STAR 130 GeV14% central (

(PRELIMINARY)

STAR 130 GeV14% central (

(*0.2)

Braun-Munzinger et al.hep-ph/0106066

Mid-rapidity ratios

Sensitivity to multi-strange baryons

T (MeV)

Rat

ios

Braun-Munzinger et al.hep-ph/0105229

Thermal fit resultsin T = 174 MeV

Model getsK/ correct,but misseson ratios!!!

Statistical errors only

+/h-

(Preliminary)

STAR 130 GeV14% central data

-/K- (7% central)

Stat. model 200 GeV predictions

Becattini et al.PRC 64 (2001) 024901

B(s) 1.27 GeV(1 s /(4.3 GeV))

s (GeV) B(MeV)

130 40.7

200 26.7

Use parameterization:

Predicts~0.8

(Preliminary)

STAR 130 GeV minbias data

(CAUTION! Really for 4 ratios)

Statistical errors only

Anti-lambda/lambda

Ratio ~ 0.76 +/- 0.02 (stat) 130 GeVRatio ~ 0.75

minbias

GeV/c2

-> p -

GeV/c2

-> p +

Preliminary STAR200 GeV minbias data

Uncorrected for absorption,which may be as much as afew percent effect.

Ratios at midrapidity, averaged over experimental acceptance in pt

Stat. Model Predictions Revisited

Becattini et al.PRC 64 (2001) 024901

B(s) 1.27 GeV(1 s /(4.3 GeV))

s (GeV) B(MeV)

130 40.7

200 26.7

Use parameterization:

(Preliminary)

STAR 130 GeV Data

(CAUTION! Really for 4 ratios) Pretty close to prediction!

(Preliminary)

STAR 200 GeV minbias data

Statistical errors only

Conclusions• Statistical model fits do well with most

particle/antiparticle ratios. • Statistical model fits do not reproduce /meson

ratios very well.– It will be interesting to see how fits in the picture.

• Quark coalescence model roughly reproduces particle ratios well.– Losing sensitivity to particle/antiparticle ratios as we

approach B=0.

• We are still not in a net baryon free region atsqrt(sNN) = 200 GeV - and perhaps still a long ways away?