Rapporteur ii global flow observables
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Rapporteur II: Global & Flow Observables. Peter Steinberg Brookhaven National Laboratory. Global Flow. Peter Steinberg BNL. Global Variables Event shape dN/d h Centrality dependence dN/d h dE T /d h  p T  Initial Energy density. “Flow” Event shape dN/d f

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Rapporteur II: Global & Flow Observables

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Rapporteur ii global flow observables

Rapporteur II:Global & Flow Observables

Peter Steinberg

Brookhaven National Laboratory


Global flow

Global Flow

Peter Steinberg

BNL


Outline

Global Variables

Event shape

dN/dh

Centrality dependence

dN/dh

dET/dh

pT

Initial Energy density

“Flow”

Event shape

dN/df

Centrality dependence

dN/df

Species

v1,v2,

Initial Pressure

Outline

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


Centrality participants vs spectators

Centrality: Participants vs. Spectators

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

“Spectators”

Only ZDCs measure Npart

Zero-degreeCalorimeter

“Participants”

“Spectators”

  • Many things scale with Npart:

    • Transverse Energy

    • Particle Multiplicity

    • Particle Spectra

Produced Particles


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

Measuring Centrality

Npart

Multiplicity in 3<|h|<4.5

  • Clearly, fluctuations affect your centrality estimator


Why we should use n part

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


Zdc as centrality device

ZDC

BBC

Percentile

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


Mutual coulomb dissociation

Reference: szdc =10.7+/-0.5 b

Measurement: (geo / tot)exp =

(Nbbc/ Ntot)exp/ bbc= (0.668  0.022)

Theory: geo / tot = (0.673  <0.034)

Mutual Coulomb Dissociation

(measured)

(from Glauber)


Multiplicity what is learned

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


Energy dependence

Energy dependence

PHENIX

STAR prelim. 10%

PHOBOS

BRAHMS prelim.


Dn d h predictions

dN/dh: Predictions

with quenching

no quenching


Dn d h post dictions

dN/dh: Post-dictions

LEXUS

  • AMPT, LEXUS, DSM, HIJING, EKRT

  • Please be careful about scaling y to h

    • Not boost invariant!

    • Not .9, .95 etc.

    • Jacobian depends on velocity: dy = b dh

    • Depends on species and mean pT!

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

AMPT


Dn d h vs centrality at h 0

dN/dh vs Centrality at h=0

dN/dh / .5Npart

Npart


Uncertainty on n part

Measurement sensitive to trigger bias

“Minimum-bias” still has bias

Affects most peripheral events

Uncertainty on Npart

% Error on Npart

This measurement

Npart

  • Estimating 96% when really 90% overestimates Npart

  • Creates “pivot point” at central events

  • Hard to rule out EKRT…


Ph obos vs enix

PH: OBOS vs. ENIX

dN/dh / .5Npart

Npart


Dn ch d h vs centrality

Octagon

Rings

dNch/dh vs. Centrality

dNch/dh

45-55%

35-45%

25-35%

dNch/dh

15-25%

6-15%

0-6%

h

h

h


Shapes of dn ch d h for different n part

Shapes of dNch/dh for different Npart

%s

Mean Npart

0-3

Data

HIJING

354

15-20

216

35-40

102

dNch/dh

dNch/dh

Data

HIJING

(dNch/dh)/(½Npart)

(dNch/dh)/(½Npart)

h

h

Systematic error ±(10%-20%)


Centrality dependence of dn ch d h h

PHOBOS Prelim.

Centrality dependence of dNch/dh|h

Solid lines: HIJING

Symbols:

Errors are systematic

|h|

<1

2-2.4

(dNch/dh)/(½Npart)

3-3.4

4-4.4

5-5.4

Npart


Total multiplicity h 5 4

PHOBOS Prelim.

Total Multiplicity (|h|<5.4)

Nch

HIJING

Npart


Multiplicity results

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/dh

    • 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…


Centrality dependence of e t

Centrality dependence of ET

PHENIX submitted

PHENIX Preliminary

  • 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…)


E t 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?

ET per charged particle

PHENIX Preliminary

PHENIX Preliminary


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

“So what’s the Energy Density?”


Rapporteur ii global flow observables

Radial flow

Not seen in angular distributions

Use HBT, spectra (T = To + m<b2> - 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

“Flow”


V 2 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

v2 from azimuthal correlations

0-5%

Df

5-15%

15-30%


V 2 versus centrality

v2 versus centrality

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

PRL 86, (2001) 402

|| < 1.3

0.1 < pt < 2.0


Centrality dependence

Centrality Dependence

midrapidity : |h| < 1.0

V2

Hydrodynamic model

Preliminary

SPS

AGS

Normalized Paddle Signal


Ceres slides

CERES slides

  • Excitation function

    • CERES 40 GeV fits in with existing energy systematics

  • Back-to-Back correlations

    • Extraction of v2 is substantially higher than normal event plane analysis


P t dependence for p p

pT dependence for p,p

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


V 2 at high p t

v2 at high pT

PHENIX Preliminary

  • 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…


Comparison of all v 2 results

Comparison of all v2 results

v2

PHENIX (pT>500 MeV)

nch/nmax


V 2 vs pseudo rapidity

v2 vs. (pseudo)rapidity

v2

v2

  • NA49 (y), PHOBOS(h) (mainly pions)

  • Different shape at midrapidity

  • PHOBOS shape similar to dN/dh!

    • Low-density limit?? v2 ~ e dN/dy

  • However, v2 appears to fall faster than multiplicity

PHOBOS Preliminary

y

h

PHOBOS Preliminary

dN/dh

h


Conclusions

Conclusions


Rapporteur ii global flow observables

ÖsNN dependence

  • Assumptions:

    in Lab in C.M.

  • Energy density (Bjorken):

  • From SPS to RHIC

    • ~50% increase in dNch/dy

    • ~50% increase in dEt/dy

    • at least 50% increase in e


Mean p t versus number of participants

Mean pt versus number of participants

  • Pions

    steep rise and plateau

  • Protons

    gradual rise and higher <pt>


Sub event correlation

Sub Event Correlation

  • Non-Flow Effects

    • Momentum conservation

    • HBT, Coulomb (final state)

    • Resonance decays

    • Jets


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