# Presentation: 659944

## Analysis of Dynamic Multiplicity Fluctuations at PHOBOS 

*Zhengwei Chai*
- Brookhaven National Laboratory
-  for the                    Collaboration
- Correlations and Fluctuations in Relativistic Nuclear Collisions
- (MIT, April 21-23,  2005)

##                    Collaboration

- Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson,
- David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane,
- Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Steven Manly, Alice Mignerey,
- Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed,
- Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith,
- Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak,
- Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres,
- Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs,  Barbara Wosiek, Krzysztof Woźniak, Shaun Wyngaardt, Bolek Wysłouch
- 	ARGONNE NATIONAL LABORATORY	BROOKHAVEN NATIONAL LABORATORY
- 	INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW	MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- 	NATIONAL CENTRAL UNIVERSITY, TAIWAN	UNIVERSITY OF ILLINOIS AT CHICAGO
- 	UNIVERSITY OF MARYLAND	UNIVERSITY OF ROCHESTER

- Zhengwei Chai

- 4-22-2005

## Outline

- Physics motivation
- Fluctuations variables *C*, ***(C)* and ***2**dyn*
- Analysis procedure for extracting *C*, ***(C)* and ***2**dyn*
- Some preliminary results
- Summary and outlook

- Zhengwei Chai

- 4-22-2005

## Fluctuations in Particle Production

- Dynamic fluctuations other than statistical and *N**part* fluctuations may provide insights on the intrinsic mechanisms of the particle production.
- Event-by-event multiplicity fluctuations could be a useful signature of the QGP-Hadron Gas phase transition due to the large difference of the degree of freedom between the two phases.
- Dynamic fluctuations are also related to particle correlations, such as jets, resonances and clusters.

**Fluctuations in Particle Production**

- Zhengwei Chai

- 4-22-2005

## Event-by-event Fluctuations Observable (C)

-  Study multiplicity fluctuation using

-  ***(C) = RMS* of *C* distribution

-  ***(C) = 1* for pure statistical fluctuations

-  *N**part* fluctuations suppressed in ***(C)*

-  ***(C)* ≠*1* indicates additional fluctuations

- Zhengwei Chai

- 4-22-2005

## Correlation Variable (C)

***(C)* measures the particles correlations
- Long range (particles from different  bins)  correlations reduce ***(C) *from 1
- Short range (particles from the same  bin) correlations increase ***(C) *from 1
***(C)* and cluster multiplicity *k *studied by UA5
- If particles are created in cluster with multiplicity *k*, and the total multiplicity in a specific  bin is increased from *N* to *kN*
- In such case, ***2**(C)=k *is a measure of cluster size if all the associated particles in cluster are included in this  bin

- Zhengwei Chai

- 4-22-2005

## C Distribution from HIJING Primaries

***C***** Distribution from HIJING Primaries**

**C**

- 1.5<||<2.0

- (C) = 1.08

- Zhengwei Chai

- 4-22-2005

## C Distribution from Rec. HIJING+GEANT Hits

***C***** Distribution from Rec. HIJING+GEANT Hits**

- 1.5<||<2.0

**C**

- (C) = 1.33

- Zhengwei Chai

- 4-22-2005

## Extraction of Dynamic Fluctuations

- Assuming
- 		***2**(C) = ****2**stat** + ****2**dyn** + ****2**det*
***2**stat** = 1* by definition
***2**det*   evaluated from various simulations
***2**(C)* calculated from reconstructed hits
***2**dyn* is a measure of particle correlations

- Zhengwei Chai

- 4-22-2005

## Octagon

**Octagon**

## PHOBOS Capability 

- in Charged Particle Multiplicity Analysis

**Octagon Multiplicity Detector Acceptance Coverage**

****

****

**Hit distribution in ********-******** space with |Z****vtx****|<10cm**

- Zhengwei Chai

- 4-22-2005

## Extracting Multiplicity Fluctuations (C)

- Octagon silicon sensors  provide
- Number of hits (*N**hit*)
- Sum of the angle-corrected deposit energy *dE *for charged particles (*E*)
*N**hit**=N**max**(1-exp(-E/E**max**))*
*E**max**/N**max*: average *dE* by a charged particle in selected ** bin
- Estimated multiplicity
-                 *N = E /(E**max**/N**max**)*

-    Multiplicities *N**1*, *N**2* in forward and backward ** bins of equal size
-      		*N**1*, *N**2*                                      ***(C)*

***Deposit Energy (E)***

***Number of hits (N******hit*****)**

- Zhengwei Chai

- 4-22-2005

## Preliminary Fluctuation Analysis Result(K.W. et el, QM04)

-  Data ***(C)* similar to
-   Rec.Hijing+Geant ***(C)*
-  Data and Rec. MC ***(C)*
-   dominated by detector
-   responses
-  Estimated systematic
-   error 5% (not shown)

- Phobos Prelim. Data
- Rec. Hijing+Geant
- Hijing (half )

******(C)**

- Zhengwei Chai

- 4-22-2005

## Preliminary Fluctuation Analysis Result

- 		(K.W. *et el*, QM04)

-  Data and Rec. MC ***(C)*
-   are similar
-  Hijing ***(C) *increases
-   with the separation in
-   pseudo-rapidity space
-  Estimated systematic
-   error 5%(not shown)

******(C)**

- 

- Zhengwei Chai

- 4-22-2005

## Preliminary Fluctuation Analysis Result

- 		(K.W. *et el*, QM04)

-  Data and Rec. MC ***(C)*
-   increase with the ** bin
-   size
-  Hijing ***(C) *increases
-   with the ** bin size
-  Estimated systematic
-   error 5%(not shown)

******(C)**

- 

- Zhengwei Chai

- 4-22-2005

## Fluctuation Sources in Rec. MC Multiplicity

-  Acceptance Effects
-  Secondaries
-  *dE/dx* Fluctuations
-  Landau fluctuation
-  Velocity (**) variation
-  Model non-statistical
-   fluctuations (physics)

- Zhengwei Chai

- 4-22-2005

## Improving Analysis for Extraction of Dynamic Fluctuations

-  Acceptance gap effects suppression with *C* offset
-  -dependent dE/dx cuts to suppress contribution
-    from secondary particles
* **1**st* order detector effects adjustment** **for dynamic
-     fluctuations extraction

- Zhengwei Chai

- 4-22-2005

## Acceptance Gap Effects in (C)

**A**

- B

**-Z**

**+Z**

***N******1A***

***N******2A***

***N******1B***

***N******2B***

-  Acceptance gap 
-    asymmetric multiplicities
-  At vertex A:
-       *N**1A* > *N**2A*  *<C>* > *0*
-    At vertex B:
-       *N**1B* < *N**2B ** <C> **<** 0*
-  Asymmetric forward and
-    backward multiplicities
-     varying mean of *C *in
-         small *Z**vtx* bin
-     significant (C) increase
-         in bigger *Z**vtx* bin

- Zhengwei Chai

- 4-22-2005

## Acceptance Gap Effects Suppression

- Event-by-event *C* offset
*-****C* is the mean of *C* distribution in a specific
-     (*Z**vtx**, ****, Centrality*) bin.
***C* suppresses the acceptance gap effects by reducing the *<C>* variation while keeping other fluctuations unchanged.

- Zhengwei Chai

- 4-22-2005

## ||<0.5

- w/o offset correction

- w/ offset correction

- C

- C

- Zvtx

- Zvtx

- Zvtx

- Zvtx

- <C>

- (C)

**|********|<0.5**

**|********|<0.5**

- Zhengwei Chai

- 4-22-2005

##  dE/dx Distributions of MC HitsBlack: Primaries + Secondaries,  Red: Secondaries,  Blue:  Primaries

-  **dE/dx Distributions of MC Hits**Black: Primaries + Secondaries,  Red: Secondaries,  Blue:  Primaries

**-3.0<********<-2.5**

**-0.5<********<0.0**

- Zhengwei Chai

- 4-22-2005

## Detector Effects from Model+Geant Simulations

**Detector Effects from Model+Geant Simulations**

- Zhengwei Chai

- 4-22-2005

## 2det 1st order dependence on 2dyn

*********2******det***** 1****st**** order dependence on ***********2******dyn***

**1.5<|********|<2.0 & half ******** acc.**

- Mod. HIJING (randomized  sign)

- Std. AMPT

- Std. HIJING

**0-20% Central**

- Zhengwei Chai

- 4-22-2005

## Extracting Dynamic Fluctuations Using Detector Effects from Simulations

***2**det0 *, **  determined by simulations

- Zhengwei Chai

- 4-22-2005

## Extracted and True Model Dynamic Fluctuations

**Extracted and True Model Dynamic Fluctuations**

- Zhengwei Chai

- 4-22-2005

## Extracted and True Model Dynamic Fluctuations

**Extracted and True Model Dynamic Fluctuations**

- Zhengwei Chai

- 4-22-2005

## Dynamic fluctuations results from 200GeV Au-Au data coming soon... 

- Zhengwei Chai

- 4-22-2005

## Summary and Outlook

-  Analyzed multiplicity fluctuations of the charged  particle production
-    in Au-Au collisions at        =200GeV over a wide pseudo-rapidity
-    range (-3.0 < **< +*3.0*)
-  The preliminary fluctuations in the Data are similar to that in
-    reconstructed Au-Au MC (HIJING+GEANT)
-  The physics fluctuations grow with increasing bin separation (**)
-    and width (**) and may be explained by intrinsic correlations in
-    particle  production.
-  Established a reliable procedure for extracting the dynamic
-    fluctuations from PHOBOS multiplicity measurement
-  Dynamic fluctuations compared with models are coming out soon!

- Zhengwei Chai

- 4-22-2005