Peter Steinberg

Rapporteur II:Global & Flow Observables

Peter Steinberg Brookhaven National Laboratory

Peter Steinberg

Global Flow

Peter SteinbergBNL

Peter Steinberg

Outline• Global Variables

• Event shape• dN/d

• Centrality dependence• dN/d • dET/d

pT • Initial Energy density

• “Flow” • Event shape

• dN/d• Centrality dependence

• dN/d• Species

• v1,v2,

• Initial Pressure

• In principle, we are looking at two important pieces of the equation of state…

Peter Steinberg

Centrality: Participants vs. Spectators

“Spectators”

Zero-degreeCalorimeter

“Spectators”

Many things scale with Npart:• Transverse Energy• Particle Multiplicity• Particle Spectra

“Participants”

Only ZDCs measure Npart

specpart NAN

The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision

Produced Particles

Peter Steinberg

Measuring Centrality• Fluctuations modify the response

• less central events fluctuate to central bins

• The final “measurement” of Npart is the best attempt to factor out the facts of life!

• In principle, we could work with % of cross section

• Final measurement of Npart is best attempt to correct for facts of life

Multiplicity in 3<||<4.5

Npa

rt

• Clearly, fluctuations affect your centrality estimator

Peter Steinberg

Why we should use Npart

• Very difficult to compare experimental results without serious estimate of Npart

• Must incorporate fluctuations in the measurement of the centrality estimators

• OK, Glauber implementation is a real uncertainty

• Even if you don’t “like” participants, the exercise is critical for inter-experiment comparisons

Peter Steinberg

ZDC as centrality device• Only shared detector

• Rates: luminosity via well-known reference process

• Timing: substantial background rejection

• Pulse height: measures centrality

• Directly confirms monotonic relationship between participants with multiplicity

ZDCBBC

Percentile

Peter Steinberg

Mutual Coulomb Dissociation• Reference: zdc =10.7+/-0.5 b

• Measurement: (geo / tot)exp = (Nbbc/ Ntot)exp/ bbc= (0.668 0.022) Theory: geo / tot = (0.673 <0.034)

(measured)

(from Glauber)

Peter Steinberg

Multiplicity: what is learned• Can the models get the “big picture” right?

• However, let’s not ignore the details…• Magnitude

• Integral over energy density, stopping, shadowing, quenching, flow

• Centrality dependence• Study effect of system size (onset of interesting effects above

critical volume)• Interplay between Npart and Ncoll

• Shape• Stopping, Final state interactions

Peter Steinberg

Energy dependence

PHENIXSTAR prelim. 10%PHOBOSBRAHMS prelim.

Peter Steinberg

dN/d: Predictionswith quenching

no quenching

Peter Steinberg

dN/d: Post-dictions

AMPT

LEXUS• AMPT, LEXUS, DSM, HIJING, EKRT

• Please be careful about scaling y to • Not boost invariant!• Not .9, .95 etc.• Jacobian depends on velocity:

dy = d• Depends on species and mean

pT!

• Still not sure who gets the champagne…wait for 200 GeV

Peter Steinberg

dN/d vs Centrality at =0dN

/d

/ .5N

part

Npart

Peter Steinberg

• Estimating 96% when really 90% overestimates Npart

• Creates “pivot point” at central events

• Hard to rule out EKRT…

Uncertainty on Npart

• Measurement sensitive to trigger bias • “Minimum-bias” still has bias• Affects most peripheral events

This measurement

% Error on Npart

Npart

Peter Steinberg

PH: OBOS vs. ENIXdN

/d

/ .5N

part

Npart

Peter Steinberg

45-55% 35-45% 25-35%

15-25% 6-15% 0-6%

dNch

/d

dNch

/d

dNch/d vs. Centrality

Octagon Rings

Peter Steinberg

Shapes of dNch/d for different Npart

dNch

/d

(dN

ch/d

)/(

½N

pa

rt)

dNch

/d

Data

HIJING

HIJING

(dN

ch/d

)/(

½N

pa

rt)

Systematic error ±(10%-20%)Systematic error ±(10%-20%)

354

216

102

Mean Npart% 0-3

15-20

35-40

Data

Peter Steinberg Npart

(dN

ch/d

)/(

½N

pa

rt)

||

<1

5-5.4

4-4.4

3-3.4

2-2.4

PHOBOS Prelim.Symbols: Solid lines: HIJING

Errors are systematic

Centrality dependence of dNch/d|

Peter Steinberg

Total Multiplicity (||<5.4)

Npart

NchHIJING

PHOBOS Prelim.

Peter Steinberg

Multiplicity Results• EKRT, HIJING disfavored by both PHENIX &

PHOBOS• Initial state saturation looks like modified Glauber

• No way to resolve using Nch alone

• What about ET?• Hydro does p dV work during longitudinal expansion,

decreases dET/d

• Eskola: “ET will be more efficient model killer”…

• So far, few papers predicting ET, but surely on the way• PHOBOS got 9 in two months after the first paper…

Peter Steinberg

Centrality dependence of ET

• ET and charged particles appear to vary in lockstep• Fits are a modified WNM, possibly allow extraction of

fraction of hard production (NB. ambiguities persist…)

PHENIX PreliminaryPHENIX submitted

Peter Steinberg

ET per charged particle

• Independent of centrality• Appears to be same as

WA98 (@SPS)

• Energy dependence• Possible 20% discrepancy betw.

NA49/WA98• Where is the increased <pT> seen by

STAR/PHENIX?

PHENIX PreliminaryPHENIX Preliminary

Peter Steinberg

“So what’s the Energy Density?”• Sorry, I won’t tell you…• Implication of PHENIX

• Constant ET/charged particle • Energy density (via Bj formula)

simply scales with multiplicity!

• (Even PHOBOS can do it!)• ~50% higher than SPS…

• Ambiguities persist• Formation time might be

substantially less

22 R

NE

ddN

RddE

ch

TchT

Peter Steinberg

“Flow”• Radial flow

• Not seen in angular distributions

• Use HBT, spectra (T = To + m<2> - Nu Xu)

• Directed flow• Forward rapidities• Not measured yet

• Sensitivity estimated at PHOBOS/STAR

• Interesting predictions for phase transition…

• Elliptic flow• Early time push,

hydrodynamic evolution • Strongest at midrapidity

y2 x2 y2 x2

2cos2 v

x

y

p

patan

Peter Steinberg

v2 from azimuthal correlations

• Method used by PHENIX

• Similar information content as Fourier method

• OK for partial acceptance• Sensitive to other correlations

• Jets (at 180o) , HBT (at 0o) But is that bad?

• CERES data

B

RC

)()(

0-5%

15-30%

5-15%)2cos(1~)( 22 vC

Peter Steinberg

v2 versus centrality

• Boxes show “initial spatial anisotropy” scaled by 0.19-0.25

PRL 86, (2001) 402

|| < 1.3

0.1 < pt < 2.0

Peter Steinberg

Centrality Dependence

Hydrodynamic model

V2

Normalized Paddle Signal

midrapidity : |h| < 1.0

SPS

AGS

Preliminary

Peter Steinberg

pT dependence for ,p

• Hydro calculations: P. Huovinen, P. Kolb and U. Heinz

Peter Steinberg

v2 at high pT

• Hydro fails at large transverse momentum• Possible interpretations suggested by jet quenching

(wait for A. Drees talk)• However, perhaps composition is a critical part of

this effect…

PHENIX Preliminary

Peter Steinberg

Comparison of all v2 results

PHENIX (pT>500 MeV)

nch/nmax

v2

Peter Steinberg

v2 vs. (pseudo)rapidity

• NA49 (y), PHOBOS() (mainly pions)• Different shape at midrapidity• PHOBOS shape similar to dN/d!

• Low-density limit?? v2 ~ dN/dy

• However, v2 appears to fall faster than multiplicity

00.010.020.030.040.050.060.070.08

0 1 2 3 4 5 6

PHOBOS Preliminary

PHOBOS Preliminary

dN/d

v 2

y

v 2

Peter Steinberg

Conclusions