Two-particle angular correlations in p+p and Cu+Cu at PHOBOS

QM2006, Shanghai Wei Li, MIT

Two-particle angular correlations in p+p and Cu+Cu at PHOBOS

Wei LiMassachusetts Institute of Technology

for the Collaboration

19th International Conference on Ultra-RelativisticNucleus-Nucleus Collisions (Quark Matter 2006),November 14-20, 2006, Shanghai, China


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 LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGYNATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

Collaboration

9 PhDs in progress！


Outline

Introductions and motivations Two-particle angular correlations in p+p Two-particle angular correlations in Cu+Cu Summary


Motivations

-6

PYTHIA p+p@200GeV-3<<3 (no weak decay)

Two-particlecorrelation function

PHOBOS MC

6


Motivations

-6

PYTHIA p+p@200GeV-3<<3 (no weak decay)

Two-particlecorrelation function

PHOBOS MC

6

No high pT trigger!

All charged particles are included (soft physics) ! Study particle correlations over a broad region -3<<3. Shed light on the gross features of multi-particle production in p+p and A+A collisions.


Experimental setup

OctagonPHOBOS apparatus


Experimental setup

Uniquely large acceptance: -3<η<3 and almost full azimuthal angle .

Single-layer silicon detector: No pT information, only (η,) of all charged particles.

Need corrections for secondary particles.

Holes for vertex detector and spectrometer: Acceptance correction needed.

PHOBOS Octagon detector:


Methodology

Two-particle correlation function:

Background:

Foreground:Event 1

Event 2

( , ) ( 1) 1, )

, )

(

(n

n

FR n

B φ φ φ Δ Δ⎛ ⎞

Δ Δ =< − − >⎜ ⎟⎝ ⎠Δ Δ

4

1 2 1 21 2 1 2

1( , ) ( , , , )

( 1)II n

n nn

dF

n n d d d d

σ φ ρ φ φσ φ φ

Δ Δ =−

:~

~


Two-particle correlations in p+p


Foreground Background

Two-particle correlation function in p+p

p+p@200GeV




p+p@200GeV

correlation function(uncorrected):



Secondary effects:-electron, conversion etc.


p+p@200GeV





corrections by MC

Secondary effects:-electron, conversion etc.

Two particle correlation function:


p+p@200GeV

-6

6


Cluster model

Isotropic cluster model: Clusters are produced at the end of the collisions. They are emitted independently. They decay isotropically in their c.m.s into

hadrons.C.Quigg, Phys. Rev. D 9, 2016 (1974)E. L. Berger, Nucl. Phys. B 85, 61 (1975).



hadrons.

Cluster model

C.Quigg, Phys. Rev. D 9, 2016 (1974)E. L. Berger, Nucl. Phys. B 85, 61 (1975).

:clusters


Cluster model


:clusters


hadrons.


Cluster model


• Cluster model is a very generic model.• It is not clear whether it has any significance in QCD. • Or it is just a phenomenological description.

:clusters


hadrons.


Cluster-like correlation structure

lower pT clusters

higher pT clusters

e.g. Resonance decay

-6

6



6

-6

average over Δ



6

-6

average over Δ

Two-particle rapidity correlation function:

short-range rapidity correlations

scale error

-6 6 Δ


Parameterize cluster size (multiplicity)

€

R(Δη ) =αΓ(Δη )

B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥

Quantitatively understand cluster phenomena


K. Eggert et al., Nucl. Phys. B 86:201, 1975



€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥€

Γ(Δη )∝ exp −(Δη )2

4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟

Decay width:

K. Eggert et al., Nucl. Phys. B 86:201, 1975



2

correlations between particles from one cluster



€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥€


4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟

Keff : effective cluster size

Decay width:



2


k: cluster sizeK. Eggert et al.,

Nucl. Phys. B 86:201, 1975

€

Keff =α +1=< k(k −1) >

< k >+1=< k > +

σ k2

< k >



€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥€


4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟

€

Keff =α +1=< k(k −1) >

< k >+1=< k > +

σ k2

< k >

€

B(Δη )Keff : effective cluster size

Decay width:

: background distribution



2


k: cluster sizeK. Eggert et al.,

Nucl. Phys. B 86:201, 1975


Cluster size and decay width

scale error

€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥

€


4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟



scale error

€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥

€

2δ

(90% C.L.)

€


4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟

Scale error:5% for Keff

4% for (90% C.L.)

Keff =

2.44±0.08

= 0.66

±0.03



Keff =

2.44±0.08

= 0.66

±0.03

scale error

On average, every charged particle is correlated with about another 1.5 particles!€


B(Δη )−1

⎡

⎣ ⎢

⎤

⎦ ⎥

€

2δ

(90% C.L.)

€


4δ 2

⎛

⎝ ⎜

⎞

⎠ ⎟


4% for (90% C.L.)


Clusters in p+p collisions

Cluster size increases with energy!

scale error

Energy dependence of Keff and

PHOBOS preliminary p+p PHOBOS preliminary





scale error UA5

ISR

HIJING

PYTHIA

PHOBOS preliminary




Expected fromresonances (UA5 collaboration)


scale error UA5

ISR

HIJING

PYTHIA

PHOBOS preliminary


Clusters in p+p collisionsEnergy dependence of Keff and


scale error

scale error

Expected fromresonances (UA5 collaboration)

PHOBOS preliminary

UA5

ISR

HIJING

PYTHIA



Cluster size increases with event multiplicity!

Multiplicity dependence of Keff and

scale error scale error

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture. QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

410GeV

200GeV



Cluster size increases with event multiplicity!

Multiplicity dependence of Keff and

scale errorscale error


Two-particle correlations in Cu+Cu


Two-particle correlations in Cu+Cu PHOBOS preliminaryPHOBOS preliminary

-6

6 6

-6

Cu+Cu@200GeV, 0%-10%p+p@200GeV



Evolution of correlation structure from p+p to Cu+Cu:• Clear elliptic flow signals which extends to very high Δ in Cu+Cu.• Similar cluster-like structure as in p+p.

PHOBOS preliminaryPHOBOS preliminary

-6

6 6

-6

p+p@200GeV Cu+Cu@200GeV, 0%-10%



Cu+Cu@200GeV



Cu+Cu@200GeV



Cu+Cu@200GeV



Cu+Cu@200GeV



Cu+Cu@200GeV



Cu+Cu@200GeV

More work will follow to subtract flow and study the medium effects on the correlation structures!


Cluster parameterization in Cu+Cu

€

R(Δη )

€

R(Δη )

€

Δ

€

Δ

€

Δ

-5 5-55

5-5

Cu+Cu@200GeV


Cluster parameterization in Cu+Cu

€

R(Δη )

€

R(Δη )

€

Δ

€

Δ

€

Δ

-5 5-55

5-5

Kef f=2.89±0.14 =0.78±0.06

Keff =2.85±0.13 =0.80±0.06

Keff =2.76±0.11 =0.81±0.05

Kef f=2.49±0.12 =0.78±0.08

Keff= 2.19±0.12 = 0.74±0.06

Extract cluster parametersin Cu+Cu using two-particle rapidity correlation function

Cu+Cu@200GeV

(90% C.L.) (90% C.L.) (90% C.L.)

(90% C.L.) (90% C.L.)


8% for (90% C.L.)


Clusters in Cu+Cu

scale error


Clusters in Cu+Cu

p+p

scale error

• To first order, cluster size in Cu+Cu is similar to p+p.


Clusters in Cu+Cu

p+p

scale error


• In Cu+Cu, cluster size decreases with centrality.


Clusters in Cu+Cu

p+p

scale error


• In Cu+Cu, cluster size decreases with centrality.

Model comparison:• AMPT shows the same trend but systematically lower in magnitude.• HIJING remains constant.


Clusters from Cu+Cu to Au+Au

€

σC2 ~ Keff

Au+Au@200GeV

peripheral

central

Phys. Rev. C74, 011901(R) (2006)

=2

Cu+Cu@200GeV

• Cluster sizes from the two methods are similar in magnitude. • Cluster sizes decrease with centrality both in Cu+Cu and Au+Au.


Clusters from Cu+Cu to Au+Au

€

σC2 ~ Keff

Au+Au@200GeV

peripheral

central

Phys. Rev. C74, 011901(R) (2006)

=2

Cu+Cu@200GeV

Ongoing studies of two-particle correlations in Cu+Cu and Au+Au!

• Cluster sizes from the two methods are similar in magnitude. • Cluster sizes decrease with centrality both in Cu+Cu and Au+Au.


Summary

Correlation structures over broad (,) range: Provide detailed information on multi-particle production.

Observed short-range correlations in p+p and Cu+Cu have a natural interpretation in terms of clusters:

Particles tend to be produced in clusters with a size of 2-3 in p+p. Clusters in Cu+Cu are similar to p+p but show a modification

of particle correlations with centrality dependence in HI collisions.


Summary

Correlation structures over broad (,) range: Provide detailed information on multi-particle production.

Observed short-range correlations in p+p and Cu+Cu have a natural interpretation in terms of clusters:

Particles tend to be produced in clusters with a size of 2-3 in p+p. Clusters in Cu+Cu are similar to p+p but show a modification

of particle correlations with centrality dependence in HI collisions.

Future work: a comprehensive study of two-particle correlations in p+p, d+Au, Cu+Cu and Au+Au!

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Two-particle angular correlations in p+p and Cu+Cu at PHOBOS

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