# Presentation: 940479

## Bulk Observables in p-p, d-Au and Au-Au at RHIC

- David Hofman
- University of Illinois at Chicago
- For the                        Collaboration

- QCD and High Energy Hadronic InteractionsMarch 28 – April 4, 2004
- XXXIXth Recontres de Moriond

##                     Collaboration (February 2004)

- Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley,
- Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski,
- Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell,
- Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman, Richard Hollis,
- Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich,
- Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Michael Ricci,
- Christof Roland, Gunther Roland, Joe Sagerer, Helen Seals, Iouri Sedykh, Wojtek Skulski,
- Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov,
- Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Siarhei Vaurynovich, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs,  Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch
- 	ARGONNE NATIONAL LABORATORY	BROOKHAVEN NATIONAL LABORATORY
- 	INSTITUTE OF NUCLEAR PHYSICS, KRAKOW	MASSACHUSETTS INSTITUTE OF TECHNOLOGY
- 	NATIONAL CENTRAL UNIVERSITY, TAIWAN	UNIVERSITY OF ILLINOIS AT CHICAGO
- 	UNIVERSITY OF MARYLAND	UNIVERSITY OF ROCHESTER

- Moriond 2004

## Charged Particle Production at RHIC

******=-ln tan ********/2**

- Pseudorapidity =  = Lorentz invariant angle with respect to the beampipe

- 0

- -1

- -2

- -3

- +1

- +2

- +3

- Beamline

- not to scale

- Moriond 2004

## A “coffee napkin” Estimate ofEnergy Density at Midrapidity.

- Total energy released in =1 is ~ 1000 GeV

****Initial Energy Density Estimate,******* *****~ 5 GeV/fm****3**

- Max initial overlap volume

- Look at all produced particles in a Central ‘Head-on’ Collision

-  = 1

- Moriond 2004

## Charged Particle Density near Midrapidity

- _Charged Particle Density near Midrapidity_

-    RHIC - combined

- Central Collisions (for Heavy Ion data)

**√****s****NN**** (GeV)**

-  “Logarithmic Rise” for AA data, above pp baseline

- Moriond 2004

## ‘PHOBOS’ Bulk Observables ≡ Low pT 

- Systematic Errors not shown

- _‘__PHOBOS’ Bulk Observables __≡__ Low p__T__ _

- arXiv:nucl-ex/0401006

- PHOBOS

- Moriond 2004

## “Participant” Scaling

**N****part****/2****  ****= 1**

_**“**__**Participant” Scaling**_

_**Binary “Collision” Scaling**_

- p + p Collisions

- Au+Au Collisions

**N****part****/2**** ****~ A**

**L~A****1/3**

**N****coll**** ****~ A****4/3**

**# of participating pairs of nucleons****≡**** N****part****/2****  **

**# of binary NN collisions**
**≡**** ****N****coll**

- Moriond 2004

## Centrality Dependence of Midrapidity  Charged Particle Yields

- _Centrality Dependence of Midrapidity  Charged Particle Yields_

- Au+Au

- 0

- 200

- 400

- 0

- 10

- 20

- dN/d/(Npart/2)

- <Npart>

-  Au+Au Centrality Dependence allows only about 10% Ncoll Scaling

- 200 GeV - ||<1

- peripheral

- central

- p+p

- Binary Collision(Ncoll) Scaling

- Participant
- (Npart) Scaling

- Moriond 2004

## Charged Particle Production at Midrapidity 

-  All RHIC energies show a similar Npart dependence

- _Charged Particle Production at Midrapidity _

- 19.6 GeV preliminary

**130 GeV**

**200 GeV**

- Data is normalized by p+p value for each energy.

- Energy and Centrality Dependence

- Au+Au

- peripheral

- central

**Participant scaling**

**Binary collision scaling**

- Moriond 2004

## Ratios to Help Cancel Systematics

- _Ratios to Help Cancel Systematics_

- Systematics Dominated by Trigger Efficiency/Centrality Determination

- Systematics

- Percentile of Cross Section

- 50

- 40

- 30

- 20

- 10

- 0

- PHOBOS, PRC 65, 061901(R) (2002)

- Ratio (200/130) = 1.14 ± 0.01 (stat) ± 0.05 (syst)

- Moriond 2004

##  Centrality Dependence of Total Charged Particle Production Nch

- _ __Centrality Dependence of Total Charged Particle Production ____N__ch___

**Pseudorapidity**

**dN/d********/<1/2 N****part****>**

**200 GeV**

**19.6 GeV**

**central**

**peripheral**

**central**

**peripheral**

**Au+Au Collisions**

-  Nch(AuAu) = (Npart/2) Nch(e+e-)

- Moriond 2004

## Pseudorapidity Distribution of Charged Particles in d + Au and p + p Collisions at 200 GeV  

- _Pseudorapidity Distribution of Charged Particles __in d + Au and p + p Collisions at 200 GeV  _

-  p + p at 200 GeV

-  d + Au at 200 GeV Min-Bias

- arXiv:nucl-ex/0311009 andSubmitted to PRL

- PHOBOS Preliminary

-  PHOBOS can measure down to very low multiplicities.

- Moriond 2004

## d+Au Centrality Dependence of dNch/d Shape

- _d+Au Centrality Dependence of dN__ch__/d____ Shape_

-  In dAu, particle production shifts to negative rapidity with increasing Npart.

- Systematic
- errors not shown

-    (4.2)

-    (15.5)

-    (2.7)

-    (7.2)

-    (10.8)

- (Normalized to Nch so can compare shape change)

- Npart

- Lines to Guide Eye Only

- Moriond 2004

## Participant Scaling in d+Au

- _Participant Scaling in d+Au_

-  Nch(dAu) = (Npart/2) Nch(pp)

- Moriond 2004

## Nch in Au-Au vs. p-p and d-Au @ 200 GeV

- ___N__ch____ in Au-Au vs. p-p and d-Au @ 200 GeV_

-  Difference in total charged particle production between Au+Au (e+e-) vs. d+Au (pp) at same collision energy

**e****+****e****-**

**Au+Au**

- Moriond 2004

## Features of the Data at High Pseudorapidity ().

- → Move to rest frame of one nucleus: i.e. ’ =  – ybeam.

- Moriond 2004

## Reminder: Limiting Fragmentation in p+p

- Data:
- UA5 (Alner *et al.*),
- Z.Phys.C33, 1 (1986)

-  Ansatz: At high collision energy, d2N/dy’dpT and particle mix, reach a limiting value and become independent of energy around beam rapidity.

- Ansatz:
- Benecke, Chou, Yang, Yen, Phys. Rev. 188, 2159 (1969)

- Moriond 2004

## Limiting Fragmentation in Au+Au

- _Limiting Fragmentation in Au+Au_

-  Growth of the Fragmentation Region with ******s****NN**

- Moriond 2004

## Limiting Fragmentation in dAu and pEmulsion Data

- dAu & pEmulsion per incident nucleon and approx. same Npart

- Npart Selection:

- p

- Em

- 1

- 2.4

- d

- Au

- 1.6x2.4

- 1.6

- _Limiting Fragmentation in dAu and pEmulsion Data_

-  Growth of the Fragmentation Region with ******s****NN** in d+Au and pEm

- R. Nouicer, QM ‘04

- Moriond 2004

## Charged Particle “Flow”: A Bulk Collective Effect

- x

- z

- y

****

**x**

**x **(defines R)

**y**

**z**

**y**

- _Charged Particle “Flow”: A Bulk Collective Effect_

- Initial _**spatial**_ anisotropy

**p****x**

**p****y**

- Final _**momentum**_ anisotropy

**dN/d(********R ****) = N****0 ****(1 + 2v****1****cos (********R****) + ****	****	****   ****2v****2****cos (2(********R****))**** + ... ) **

- Moriond 2004

## Directed Flow (v1) In Beam Rest Frame

**In target frame of reference, directed flow exhibits signal consistent with limiting fragmentation**

- _Directed Flow (v__1__) In Beam Rest Frame_

-  Limiting Fragmentation Behavior in Directed Flow

- S. Manley, 20th Winter Workshop

- Moriond 2004

## Elliptic Flow (v2) In Beam Rest Frame

-   PHOBOS Preliminary*** *****v****2****200**

-  PHOBOS*** *****v****2****130 **

- _Elliptic Flow (v__2__) In Beam Rest Frame_

- S. Manley, 20th Winter Workshop

**v****2**

-  Limiting Fragmentation Behavior in Elliptic Flow

******’**

- Moriond 2004

## Experimental SummaryBulk (charged particle) Observables at RHIC

- Scaling of multiplicity data with Npart/2 in Au+Au and d+Au.
- Per participant pair, Au+Au reaches e+e- total particle production level at RHIC energies.  d+Au reaches p+p level (at the same collision energy).
- “Limiting fragmentation” of charged particle multiplicity yields (dN/d) observed in Au+Au and d+Au at RHIC.
- “Limiting fragmentation” of azimuthal angular distribution of charged particles (v1 and v2) observed at RHIC.

- Moriond 2004