Energy and Centrality Dependence of Mid-Rapidity Charged Particle Multiplicity Measured with

Energy and Centrality Dependence of Mid-Rapidity Charged Particle

Multiplicity Measured with

DNP02

Aneta Iordanova

University of Illinois at Chicago

Collaboration

ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa

BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov

INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak

MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin Ballintijn, Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres, Robin Verdier, Bernard Wadsworth, Bolek Wysłouch

NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang

UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer

UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey,

Marguerite Belt Tonjes

UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

•4 Multiplicity Array

Octagon, Vertex and Ring Counters

•Mid-rapidity Spectrometer

•TOF wall for high momentum PID

•Triggering

Scintillator Paddle Counters

Zero Degree Calorimeter (ZDC)

Čerenkov Counters

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Vertex Detector8192 silicon channels • Outer Layer: 2 × 2048 channels, 0.47mm × 24.1mm• Inner Layer: 2 × 2048 channels, 0.47mm × 12.0mm

Top

Bottom

62.1mm

50.4mm

Z,

Beam pipe

1 channel

Y

X

Used for• reconstruction of collision location (“vertex”)• multiplicity measurement

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Inner Layer

Outer Layer

TrackletTwo-hit combinations from Outer and Inner Vertex (Top or Bottom), pointing to the reconstructed vertex.

ReconstructedVertex

hit

hit

Top VertexTop Vertex

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First Pass

Second Pass

Tracklet Reconstruction

Seed Layer

Search Layer

Reconstructed Vertex

hit

hit

Search ,Search

Extrapolate Seed ,Seed

• || = |Search – Seed| < 0.3

• || =|Search – Seed| < 0.1

• smallest combination.

Tracklets with a common hit in the “Search Layer”

•smallest combination.

Top VertexTop Vertex

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etsted_tracklreconstruc1||charged 1

1N

d

dN

Multiplicity Determination using Vertex detector

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Efficiency Correction

Factor

Combinatorial Background

depends on:•Azimuthal acceptance of detector• Z vertex position

• Multiplicity in detector (hits)

Inner Layer

Inner Layer

Outer Layer

Outer Layer

Nominal vertex position

Bottom

Top

Efficiency Correction Factor ((from Monte Carlo)

~ 0.4 (Z=0cm) to 0.25 (Z=10cm)

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Efficiency Correction Factor for three different Zvertex positions19.6 GeV

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Combinatorial Background Tracklets ()

Nbackground_tracklets= Nreconstructed_tracklets

etsted_tracklreconstruc1||charged 1

1N

d

dN

T R U E

Z,

Beam pipe

Tracklets from hits by rotating Inner layers 1800 about the beam pipe.

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Monte CarloData

Background Tracklets for 80 to 100 Hits in Outer Vertex Layer 19.6 GeV

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Cou

nts

Cou

nts

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions

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200GeV

130GeV

19.6GeVPRELIMINAR

Y

||<1

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions(Two component fit)

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200GeV

130GeV

19.6GeVPRELIMINAR

Y

||<1

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Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions

(Normalized by the corresponding pp value for each energy)

200GeV

130GeV

19.6GeVPRELIMINAR

Y

||<1

Errors from Au+Au only

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions

(KLN saturation model)

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200GeV

130GeV

19.6GeVPRELIMINAR

Y

||<1

PHOBOS 19.6 GeV

Comparison of central charged-particle multiplicity for different energies.

PRELIMINARY

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Conclusion

• Phobos has measured charged-particle multiplicity dependence on centrality and energy in Au-Au collisions at √sNN of 200,130 and 19.6GeV.

• The mid-rapidity scaled charged-particle multiplicity shows evidence for deviation from Npart scaling over the studied centrality range.

• The mid-rapidity scaled charged-particle multiplicity dependence on energy follows the logarithmic rise.

DNP02 Aneta Iordanova