Alexander Milov Weizmann Institute, Israel
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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__
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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.
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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.
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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%
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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(
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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)
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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
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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
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Transverse energy per charged particleTransverse energy per charged particle
dEt /dNch independent of sNN
dEt /dNch independent of Npart
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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
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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
.