Spin-Flavor Decomposition

J. P. Chen, Jefferson Lab PVSA Workshop, April 26-27, 2007, Brookhaven National Lab

Polarized Inclusive DIS, u/u and d/d from A1n/A1

p

Spin-Flavor decomposition in high-x (valence) region

Polarized Semi-Incluisve DIS

Spin-Flavor decomposition in moderate-x region

Polarized Parity-Violating DIS

A new window to study sea quark polarization

JLab 12 GeV upgrade and a large acceptance solenoid detector

A powerful tool for nucleon spin-flavor decomposition

Unpolarized and Polarized Structure Functions

Unpolarized Parton Distributions (CTEQ6)• After 40 years DIS experiments, unpolarized structure of the nucleon reasonably

well understood.• High x valence quark dominating

NLO Polarized Parton Distributions (AAC06)

Polarized Inclusive DIS

Valence Quark Spin-Flavor decomposition at high x

World data for A1 World data for A1

Proton Neutron

Precision A1n at High x from Hall A

E99-117

• First precision A1

n data at high x

• Extracting valence quark spin distributions

• Test our fundamental understanding of valence quark picture• SU(6) symmetry• Valence quark models• pQCD (with HHC) predictions

• Quark orbital angular momentum• Crucial input for pQCD fit to PDF• PRL 92, 012004 (2004)• PRC 70, 065207 (2004)

A1p/A1

d Results from CLAS

xbj

A 1p

HF perturbed QM

World Data parm Q2 = 10 GeV2

Spin 3/2 suppression Helicity 3/2 suppression

Symmetric Q Wave function

SLAC - E143

SMC

HERMES

SLAC - E155

CLAS-EG1b Q2 = 1.0 - 4.52 GeV2

SU(6)

pQCD

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1xbj

A 1d ( D

-sta

te c

orre

cted

) HF perturbed QM

World Data Parm + d WF Q2 = 4.2 GeV2

World Data parm Q2 = 10 GeV2

Spin 3/2 suppression

Helicity 3/2 suppression

Symmetric Q Wave function suppression

SLAC - E143

SMC

HERMES

SLAC - E155

CLAS-EG1b Q2 = 1.0 - 4.52 GeV2

SU(6)

pQCD

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Proton

Deuteron

Naïve Extraction of Polarized Quark Distributions

• Combining A1n and A1

p results• Valence quark dominating at high x• u quark spin as expected• d quark spin stays negative!

• Disagree with pQCD model calculations assuming HHC (hadron helicity conservation)

• Quark orbital angular momentum

• Consistent with valence quark models, pQCD PDF fits without HHC constraint, statistic model

• Consistent with a new model from Feng Yuan et al. including OAM

A1p at 11 GeV

Projections for JLab at 11 GeV

A1n at 11

GeV

Spin Structure with the Solenoid at JLab 12 GeV

• Program on spin structure with polarized target(s) and a solenoid highest polarized luminosity: ~1036

A solenoid with detector package (GEM, Lead-glass+ Cherenkov)

large acceptance: ~700 msr for polarized

high luminosity and large acceptance Inclusive DIS: improve by a factor of 10-100

A1 at high-x: 200 hours, high precision

parity violating spin structure g3/g5 : first significant measurement SIDIS: improve by a factor of 100-1000

spin-flavor decomposition (~2 orders improvement)

transversity and TMDs,

3He target

Solenoid detector for (SI)DIS

GEMs

Gas Cerenkov

Calorimeter

GEMs

• With Standard HMS+SHMS,

1800 hours

(X. Zheng)

• With Solenoid,

200 hours

Polarized Semi-inclusive DIS

Spin-Flavor decomposition at moderate x

uv and dv at JLab 11 GeV

Flavor decomposition with SIDISFlavor decomposition with SIDIS•With standard HMS+SHMS(see X. Jiang’s Talk) compared with HERMES

With Solenoid, 2 orders of magnitude improvement

Polarized Sea with SIDISPolarized Sea with SIDIS

Polarized Sea

JLab @11 GeV

•With standard HMS+SHMS (X. Jiang’s talk) compared with HERMES

With Solenoid, 2 orders of magnitude improvement

Polarized Parity Violating DIS

Sea quark polarization

Longitudinal Target Single Spin Asymmetry

• Unpolarized beam on longitudinally polarized target

keep Z interference terms, neglect Z2 terms

})2(]))(1[({

16

152

43

2

4

2

ZA

ZZZV

Z

Q

gyxyggxyggyg

MEdxdy

d

dxdy

d

g1Z term can be eliminated by using positron beam

PV-SSF in Naïve Parton Model

• Naïve Parton Model:

0

)()(22

)()(

4

53

1

Z

qqAq

ZZ

qqVq

Z

g

qqgexxgg

qqgeg

ZA

ZV gyxyggyyg

dxdy

d

dxdy

d 13

22

)2()2

11(

Put back into the general formula, we get

g3 provides access to polarized sea quark distributions.

Potential access to polarized strange quark distributions.

Measure PV-TSSA with the Selonoid

• At x=0.2, Q2=2.4, y=0.58, A~ 10-5-10-4

• Need high luminosity and large acceptance• Rate estimation with the Solenoid detector:

1000 hours beam, statistical precision for asymmetry

will be a few x 10-5. A significant first measurement (~ a few )

Projection of Collins/Sivers Asymmetries vs PT and x for + (60 days)

• For one z bin

(0.5-0.6)

• Will obtain 4

z bins (0.3-0.7)

• Also - at same

time

• With upgraded

PID for K+ and K-

Summary

Spin-Flavor decomposition:• Polarized inclusive DIS in high-x region

• Valence quark polarization

• Polarized semi-inclusive DIS in moderate-x region• Valence and sea quark polarization

• Polarized parity violating DIS• A new tool to study sea quark polarization

• A large acceptance solenoid with high luminosity• 700 msr, 1036 polarized (n) luminosity• Improvement of a factor of 10-100 in acceptance*luminosity