04/22/2006 DIS2006, M. LIU

Overview of Longitudinal Spin

Physics at PHENIX

Ming Xiong Liu

Los Alamos National Lab

(PHENIX Collaboration)

04/22/2006 DIS2006, M. LIU

The Relativistic Heavy Ion Collider

at Brookhaven National Laboratory

R-HINew state of matter

QGP

De-confinement

…

polarized protonNucleon Spin Structure

Spin Fragmentation

pQCD

…

RHIC is a QCD lab

PHENIX

STAR

BRAHMS

04/22/2006 DIS2006, M. LIU

• Proton Spin - a major puzzle from polarized DIS experiments

– Proton Spin Decomposition

• Origin of Proton Spin:– gluon, sea quarks, orbital angular momentum ?

– DIS can’t directly probe gluons and anti-quarks @LO

• a new tool : RHIC-SPIN– a polarized proton collider

– quark-gluon, quark-quark and gluon-gluon interactions

– directly explore gluon and sea quark distributions

04.031.0 ±=

gqLG +++=2

1

2

1

Experimentally

RHIC-Spin PhysicsRHIC-Spin Physics

New Frontier of Nucleon Structure ResearchNew Frontier of Nucleon Structure Research

04/22/2006 DIS2006, M. LIU

History of Spin Runs

s = 200 GeV Polarization Recorded L Recorded LP4

2001-2002 transverse-spin run

15% 0.15 pb-1

first polarized proton collisions

2003 longitudinal-spin run

27% 0.35 pb-1 1.5 nb-1

spin rotators commissioned, AGS p-C CNI polarimeter

2004 commissioning run (longitudinal spin)

40% 0.12 pb-1 3.3 nb-1

AGS warm snake commissioned, gas-jet absolute polarimeter

2005 longitudinal-spin run (w/ short transverse run)

47% 3.8 pb-1 205 nb-1

AGS cold snake installed

2006 transverse and longitudinal spin run

60% in progress in progress2005 – First “long” longitudinal-spin polarized-proton run: Figure of merit (LP4)

more than 40 times larger than that of previous runs

04/22/2006 DIS2006, M. LIU

The PHENIX Detectors• Philosophy

– high resolution & high-rate at the

cost of acceptance

– trigger for rare events

• Central Arms

– | | < 0.35, ~

– , 0, e, +-, ... – Identified

– Momentum, Energy

• Muon Arms

– 1.2 < | | < 2.4

– Momentum (MuTr)

04/22/2006 DIS2006, M. LIU

Experimental Observables

)()(

)()(

)()(

)()(

++

+

++++

+++

=

=

L

LL

A

A

• Asymmetries

)()(

)()(

)()(

)()(

+

+

=

=

T

TT

A

A

04/22/2006 DIS2006, M. LIU

ALL @RHIC-SPIN• Polarized hadron collisions

– double longitudinal spin asymmetry

– leading-order gluon interactions

• direct-photon production

• heavy-flavor production

• Other channels with light hadrons

proton beam

proton beam

or

or

gluon

photon

proton beam

proton beam

or

or gluon

gluonheavy flavor

ALL =++ +

++ +fAa (xa ,Q

2) fBb (xb,Q

2)d ab

cd

dt

04/22/2006 DIS2006, M. LIU

Heavy Quark Production @RHIC Sensitive to gluon polarization: g(x)

Gluon Fusion dominates at LO

PYTHIA estimate:

92:897:3500

85:1595:5200

BeautyCharmGeV

Double spin asymmetry:

QQgg

LLLL axg

xg

xg

xgA

)(

)(

)(

)(

2

2

1

1

Decay modes:

e+e-, μ+μ-, eμ, eX, μX1.5

2

5

aLL

Karline

r & R

obine

tt, Phys.L

ett.B

32

4 (19

94

)

J/ μμ

bb eμX

cc eX

x

(gg QQ ) : (qq QQ )

ˆ s

MQ

=1.1

04/22/2006 DIS2006, M. LIU

J/ production mechanism

• LO NRQCD:

]})()()2

11(

9[)2,

4()2,(

32

15

)()1()2,4

()2,(

{27

0

1)(/

80

3)(/

802

1

2

1

1

3)(/

80

1

2

1

1

1

1

2

23

))(/(24

><><+

><

SOPOm

msx

mfmxf

SOmsx

mfmxf

x

dx

ms

JJ

gg

J

qq

sJpp

sm

mix of various

processes

2~

s

04/22/2006 DIS2006, M. LIU

ALL vs pT

Log(x)

XJgg

LLLL axg

xg

xg

xgA

+/

2

2

1

1

)(

)(

)(

)(

• J/ : produced via almost pure gluon fusion

• sensitive to gluon polarization

• expect x100 improvement in the future

04/22/2006 DIS2006, M. LIU

Direct Photon

• A Golden channel– Sign and magnitude(x)

proton beam

proton beam

or

or

gluon

photon

ALL = ++ +

++ + +

~G

G

q

q

04/22/2006 DIS2006, M. LIU

More on ALL

Jet ALL

Direct photon

, h±, electron, μ, , ...

Fukao’s talk

04/22/2006 DIS2006, M. LIU

Sea Quark Polarization & Flavor

Asymmetry

)()(

)()(

?

xdxu

xdxu

=

• Nucleon is a complex system• Sea quarks and gluons correlated• QCD dynamics

FermiLab/E866

d (x) u (x)

d (x)=?

u (x)

04/22/2006 DIS2006, M. LIU

Sea Quark Polarization

• Pion cloud model:

• Chiral soliton model:

0=du

)(~ duNduC

04/22/2006 DIS2006, M. LIU

W Production and AL @500GeV

Bunce G. et al, hep-ph/0007218

μ+

μ-

04/22/2006 DIS2006, M. LIU

Summary and Outlook

• Very rich physics program with longitudinally polarized beams– Spin Puzzle

• Polarized gluon distribution

• Flavor-dependent polarized quark distributions

– Excellent QCD test ground with polarized partons

• Latest news from PHENIX:– Light hadron production:

– Heavy quark production: J/Psi, open charm …

– Explore orbital angular momentum: jet correlation?

– Run6 500GeV test run: first W events @RHIC

• Where does the nucleon get its spin?– Still don’t know … but RHIC-SPIN will help us to find the answer

– and we will learn a lot more about the nature of strong interactions

, , , ...

04/22/2006 DIS2006, M. LIU

Backup

04/22/2006 DIS2006, M. LIU

Orbital Angular Momentum

• Back-to-back jet correlation

04/22/2006 DIS2006, M. LIU

What do we learn from ALL?

• Asymmetries

• Polarized Quark and

Gluon Distributions

• Proton Structure

– QCD dynamics

dt

dQxfQxf

dp

dE

cd

abb

b

Ba

a

A ),(),( 22

3

3

=

1

0)(

)()()(

dxxff

xfxfxf

04/22/2006 DIS2006, M. LIU

PHENIX forward upgrade

100901998036000rejection

<2.0<1.0<0.7( ) deg

Achieved enough trigger rejection

•increase of pion rejection via isolation

cut

• possible background rejection via

reconstructing W transverse mass.

• possible improve of momentum

resolution with well defined determined

vertex.

RPC LL1 trigger

(NSF proposal)

MuTr LL1 trigger

(Funding in Japan)