Alexander Milov Weizmann Institute, Israel

Alexander Milov Weizmann Institute, IsraelAlexander Bazilevsky RIKEN BNL Research Center , USAKlaus Reygers University of Münster, Germany

for the PHENIX Collaboration

Nucl-exp/0012008 (submitted to PRL) QM2001 poster P179

Charged Particle Multiplicity and Charged Particle Multiplicity and Transverse Energy in Au+Au Collisions at Transverse Energy in Au+Au Collisions at

ssNNNN = 130 GeV = 130 GeV__

OutlineOutlineIntroduction:

Importance of Nch

and Et measurements

The PHENIX detector.

Experimental results:

dNch/d distribution at mid-rapidity

dEt /d distribution at mid-rapidity

Centrality determination

Results and discussion:

Comparison to model predictions

Comparison to CERN and AGS data

Summary.

Global variables: Global variables: EEt t and and NNchch

Initial conditions, energy density of the system.

Scaling with s.

Mechanism of particle production, soft vs hard?

Soft: Nch Npart

Hard: Nch Ncoll

Constrain theoretical predictions.

Theoretical PredictionsTheoretical Predictions

Various models predict different trends for (dNch/d /Npart

vs Npart

:

HIJING: (Wang, Gyulassy,

nucl-th/0008014) (dNch /d

/Npart

increases

with Npart

Saturation model: (Eskola, Kajantie, and Tuominen

hep-ph/0009246) (dNch /d

/Npart

constant

vs Npart

PHENIX-Setup: Beam View PHENIX-Setup: Beam View Pad Chambers:

RPC1 = 2.5 m RPC3 = 5.0 m

|| < 0.35, = 90o

8 x 4320 pads.

> 99%, ~ 2 mm

Lead Scintillator EMCal.

REMCal = 5.1 m.

|| < 0.38, = 45o

2 x 2592 PMT

18X0, ~ 8% for 1GeV -quanta

PHENIX-Setup: Side ViewPHENIX-Setup: Side View

Zero Degree Calorimeters

Spectator neutrons with || > 6

|Z|=18.25 m

Beam Beam Counters

64 Cherenkov quartz counters with PMT readout

3.0 < || <3.9 = 360o

Trigger and event selectionTrigger and event selectionBBC trigger:

Coincidence of both BBC (at least two photomultipliers fired in each BBC).

Corresponds to (92 ± 2)% of the geometrical Au-Au cross section (geo. = 7.2 b).

ZDC trigger:

Coincidence of both ZDC (E > 10 GeV)

Includes mutual Coulomb dissociation processes

97.8% of the BBC trigger events also satisfy ZDC trigger condition.

Event vertex restriction:

|Z| < 20 cm around centre of interaction region.

Charged Multiplicity DeterminationCharged Multiplicity DeterminationProcedure: count tracks on a statistical basis, no explicit track reconstruction :

Combine all hits in PC3 with all hits in PC1.

Project resulting lines onto a plane through the beam line.

Count tracks within a given radius.

Determine combinatorial background by event mixing

B=0

Track Vertex DistributionTrack Vertex Distribution

Number of tracks per event:

Subtract average background on an event-by-event basis

Count all tracks within R=25 cm ( => 95.9% of all tracks)

3 contributions:

Peak at low R: primary particles coming from the event vertex

Combinatorial background: dNB/dR R

Exponential tail: in-flight decays

Tracks outside acceptance window: 4.3%

Pad Chamber inactive regions: 15.3%

Double hit resolution:

13.6% for most central events

3.6% to the subtracted background

Correction due to particle decays

Primary charged particles (±) decays in-flight,

Neutral (K0, 0…) particles feed-down: . . Net correction: 2.8% based on HIJING

CorrectionsCorrections

Minimum-bias multiplicity distribution Minimum-bias multiplicity distribution at at ssNNNN = 130 GeV = 130 GeV

92% of geo (Missing events are all in the lowest bins)

Shape at high multiplicities determined by fluctuations due to limited acceptance.

Scaling factor (geometry) to one unit of rapidity 5.82 (lower axis).

PHENIXAu-Aus

NN = 130 GeV

o peak at

136.7 MeV/c2

Energy scale:

EMCal measures full energy of and e±

Slow hadrons are absorbed in EMCal

Relativistic hadrons produce MIP peak

EMCal energy response proportional to Et :

Et = 1.17 ±0.05 EtEMCal

EMCal energy resolution not important for the Et measurement

Red curve: Au-Au data. MIP peak at

270 MeV

Blue curve is AGS test beam data with +

EMCal energy responseEMCal energy response

Background sourcesBackground sources

25.0

38.0

EMC

EMC

E

E

Background from albedo

Background from decays

From simulations

From events with displaced vertex.

MCData

Minimum-bias transverse energy Minimum-bias transverse energy distribution at distribution at ssNNNN = 130 GeV = 130 GeV

PHENIX preliminaryAu-Aus

NN = 130 GeV

92% of geo (Missing events are all in the lowest bins)

Shape at high multiplicities determined by fluctuations due to limited acceptance.

Scaling factors: Transformation 1.17 Dead areas 1.03 Geometry 10.6

Minimum-bias multiplicity distribution Minimum-bias multiplicity distribution at at ssNNNN = 130 GeV = 130 GeV

92% of geo (Missing events are all in the lowest bins)

Shape at high multiplicities determined by fluctuations due to limited acceptance.

Scaling factor (geometry) to one unit of rapidity 5.82 (lower axis).

PHENIXAu-Aus

NN = 130 GeV

Centrality dependenceCentrality dependence

Use BBC – ZDC response to define centrality cuts (in 5% bins of geo)

Determine <dN

ch /d> and <dE

t

/d> vs centrality

PHENIX preliminaryPHENIX preliminary

0-5%

5-10%

10-15%15-20%

dRr

r o

exp1

1)(

fmAAR )03.065.6(61.119.1 3/13/1

Calculation of Calculation of NNpartpart and and NNcollcoll

Use simulated BBC – ZDC response to define centrality cuts.

Relate them to Npart and Ncoll using Glauber model.

Straight-line nucleon trajectories

Constant NN=(40 ± 5)mb.

Woods-Saxon nuclear density:

fmd )01.054.0(

Centrality dependenceCentrality dependenceData shows clear increase of dNch/dper participant vs Npart

In contrast with EKRT saturation model

Similar to HIJING (although data ~15% higher)

Particle production mechanismParticle production mechanismcollpart NBNAddX

0

PHENIX preliminaryPHENIX preliminary

28.088.0 A

12.034.0 B

)(24.080.0 GeVA )(09.023.0 GeVB

Consistent results:

Hard processes contribution increases with centrality:

from ~30% mid-central to ~50% most central

19.038.0/ AB 18.029.0/ AB

PHENIX preliminaryPHENIX preliminary

Comparison to CERN resultsComparison to CERN results

partNddX

0

WA97

Transverse energyMultiplicity-value

WA98

PHENIX 04.016.1 05.013.1 04.007.1 05.005.1

06.008.1

Transverse energy per charged particleTransverse energy per charged particle

dEt /dNch independent of sNN

dEt /dNch independent of Npart

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

ssNNNN dependence dependence

d

dX

dy

dX

d

dX

dy

dX1.1

dy

dE

Rt

2

1

cfm

AR

/1

12.1 3/1

SummarySummary

Centrality dependence of particle dNch /dand dEt /d have been measured in s

NN = 130 GeV Au+Au collisions.

Both dNch /dand dEt /d per participant increase with centrality:

in qualitative agreement with HIJING

in contrast to EKRT saturation model prediction

the increase is stronger than at SPS

dEt /dNchis independent of centrality and of sNN

.