# Presentation: 818892

## Charged Particle Multiplicities from Cu+Cu, Au+Au and d+Au Collisions at RHIC

- Aneta Iordanova
- University of Illinois at Chicago
- for the                      collaboration

## Phobos Collaboration

- Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel,
-  Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova,  Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey,
- Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov,
- Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs,  Barbara Wosiek, Krzysztof Woźniak, 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

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## PHOBOS detector

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Outline

- Control parameters of a heavy ion collision
- Energy
- 19.6 - 200 GeV
- Colliding system size
- centrality Npart from 3.5 (d+Au) – 360 (Au+Au)
- Species
- p+p, d+Au, Cu+Cu and Au+Au
- Global features of charged particle production (observables)
- dNch/d shapes (particle distributions in )
- Mid-rapidity factorization

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Data

- comparison of Au+Au and Cu+Cu
- d+Au and p+p

## Charged hadron dNch/d distribution

**d+Au**

- Charged hadron dNch/d distribution

- centrality

**Au+Au : PRL **** 91, 052303 (2003) **
**Au+Au : PRC 74, 021901 (2006)**
**  **** ****d+Au :**** PRC 72, 031901 (2005)**

- dN/d distribution

- preliminary

- preliminary

**Au+Au data**

**Cu+Cu data**

- With energy:
- Height increases
- Width increases (in  space)
- With centrality(0-50% central):
- Height increases
- With species:
- Same systematic trends

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Comparison of Au+Au and Cu+Cu

- For the same collision system size (Npart) dNch/d shape is very similar for
- central Cu+Cu with mid-central Au+Au collisions
- mid-central Cu+Cu with peripheral Au+Au collisions

**200 GeV**

- dN/d distribution

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Comparison of Au+Au, d+Au and p+p collisions at 200 GeV

- Scale by Npart/2
- allows for a direct comparison to p+p
- i.e. normalized to 1 participating pair
- Multiplicity obtained at the same center-of-mass energy is similar in p+p and d+Au
- Multiplicity is larger for Au+Au collisions at the same energy

- dN/d distribution

**d+Au : PRL **** 93, 082301 (2004)**

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Comparison of d+Au and p+p

- More detailed comparison of d+Au and p+p shows
- More peripheral collisions tend toward p+p shape

- dN/d distribution

**-6       -4       -2         0         2        4         6**
**                                                            ****η **

- PHOBOS d+Au and p+p
- Data at √s = 200 GeV

**0**

**1**

**2**

**3**

**d+Au : PRC 72, 031901 (2005)**
**p+p  **** **** : 2004 J.Phys.G 30 S1133-1137**

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## factorization

- at midrapidity
- in energy and centrality

## Measured pseudorapidity density per participant pair as a function of Npart

- 200 GeV (UA5)

***90 % C.L.***

- 19.6 and 62.4 GeV (ISR)

- Mid-rapidity factorization

- Measured pseudorapidity density per participant pair as a function of Npart

- 0-50% cross-section

- Mid-rapidity dNch/d
- Information about the created matter →energy density
- Particle production in A+A: interplay between collision centrality (geometry) and collision energy?
- balance of binary/soft processes

**Au+Au : PRC 74, 021901 (2006)**

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Midrapidity Ratios

- 200/19.6

- 200/62.4

- 200/130

**Cu+Cu**
**preliminary**

**Au+Au**

- PHOBOS

- HIJING

- Saturation

- Data ratio 200/X
- no centrality (geometry) dependence
- Models
- HIJING
- disagrees with data
- Saturation Model (KLN)
- flat centrality dependence as in data

- Mid-rapidity factorization

- KLN

**HIJING:**Comput.Phys.Commun. 83 (1994) 307,v 1.35
**KLN:** Phys.Lett.B523 79 (2001) & arXiv:hep-ph/0111315

**Au+Au : PRC 74, 021901 (2006)**

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## factorization

- at midrapidity
- versus pT

## Transverse Momentum Factorization

- So far discussed factorization of bulk matter
- ~pT<1GeV/c
- Can look at differential factorization for pT bins

- pT factorization

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Transverse Momentum Factorization

**Au+Au**

**Cu+Cu**

**Au+Au: PRL**** ****94, 082304 (2005)**

**<p****T****> = 0.25 GeV/c**

**<p****T****> = 1.25 GeV/c**

**<p****T****> = 2.5 GeV/c**

**<p****T****> = 3.38 GeV/c**

**<p****T****> = 3.88 GeV/c**

- Ratio of charged hadron yields in 200 and 62.4 GeV
-  factorization up to pT ≈ 4 GeV/c for Npart > 40

- pT factorization

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## Summary

- PHOBOS has measured multiplicity for
- large systematic dataset
- -5.4<η<5.4
- 2 to 360 participants
- √s = 19.6 to 200 GeV
- Au+Au and Cu+Cu data are similar at the same Npart
- Scaling and factorization properties are found in the Au+Au data
- extended longitudinal scaling
- mid-rapidity factorization in bulk yield and versus pT
- seem to persist into the Cu+Cu collision system
- Observed factorization in energy and centrality is seen in multiplicity and versus pT
- implies that this is set at an early stage of the collision and is connected with the geometry of the collision

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006

## The End

## Ratio of yield for 200 and 62.4 GeV is centrality independent for all measured pT bins

- Ratio of yield for 200 and 62.4 GeV is centrality independent for all measured pT bins

- Transverse Momentum Factorization

- pT factorization

**Data from PRL 94, 082304 (2005)**

- Aneta Iordanova

- DNP, Nashville, 28 Oct 2006