# Presentation: 132811

## Energy and Centrality Dependence 

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

- Aneta Iordanova
- University of Illinois at Chicago

## Collaboration

- 	_ARGONNE NATIONAL LABORATORY_	Birger 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, KRAKOW_	Andrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski,
- 		Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak
- _	__MASSACHUSETTS INSTITUTE OF TECHNOLOGY_	Maartin 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, TAIWAN_	Chia Ming Kuo, Willis Lin, Jaw-Luen Tang
- 	_UNIVERSITY OF ILLINOIS AT CHICAGO_	Russell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer
- 	_UNIVERSITY OF MARYLAND_	Abigail Bickley, Richard Bindel, Alice Mignerey,
- 		Marguerite Belt Tonjes
- 	_UNIVERSITY OF ROCHESTER_	Joshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly,
- 		Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs

## 4 Multiplicity Array

- 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

## Vertex Detector

- 8192  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

*Outer Layer*

*Inner Layer*

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

## Tracklet

**Tracklet**

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

*Reconstructed*
*Vertex*

- hit

- hit

- Top Vertex

## Tracklet Reconstruction

- 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 Vertex

## Multiplicity Determination using Vertex detector

## Efficiency Correction Factor (

- Azimuthal acceptance of detector
-  Z vertex position
-  Multiplicity in detector (hits)

- Efficiency Correction Factor (
- (*from Monte Carlo*)

-  ~ 0.4 (Z=0cm)  to 0.25 (Z=10cm)

## Efficiency Correction Factor for three different Zvertex positions

*Efficiency Correction Factor for three different Z**vertex **positions*
*19.6 GeV*

****

## Combinatorial Background Tracklets ()

- Combinatorial Background Tracklets ()

*N**background_tracklets****= ****N**reconstructed_tracklets*

**T       R       U       E**

- Z, 

*Beam pipe*

- 

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

## Background Tracklets  for 80 to 100 Hits in Outer Vertex Layer 

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

- 

- 

- Counts

- Counts

- 

## Scaled charged-particle multiplicity as a function of Npart 

*for Au+Au collisions*

**|********|<1**

## Scaled charged-particle multiplicity as a function of Npart 

*for Au+Au collisions*
*(Two component fit)*

**|********|<1**

## Scaled charged-particle multiplicity as a function of Npart 

*Scaled charged-particle multiplicity as a function of Npart *
*for Au+Au collisions*
*(Normalized by the corresponding pp value for each energy)*

**200GeV**

**130GeV**

**19.6GeV**

- PRELIMINARY

**|********|<1**

**Errors from Au+Au only**

## Scaled charged-particle multiplicity as a function of Npart 

*for Au+Au collisions*
*(KLN saturation model)*

**|********|<1**

## Comparison of central charged-particle multiplicity 

**PHOBOS 19.6 GeV**

*Comparison of central charged-particle multiplicity *
*for different energies.*

- PRELIMINARY

## Conclusion

-  Phobos has measured charged-particle multiplicity dependence on centrality and energy in Au-Au collisions at *√s*NN 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.