Spin Structure with JLab 6 and 12 GeV

J. P. Chen, Jefferson LabINT-12-49W: Workshop on Orbital Angular Momentum in QCD, Feb. 6, 2011

Overview

Selected Results from JLab 6 GeV

A1 at High-x: Valence Quark Spin Distributions

Moments

g2 /d2: B-C Sum Rule, Color Lorentz Force (Polarizability)

SIDIS: Transversity and Flavor Decomposition

Planned experiments with JLab 12 GeV

Introduction

• Spin experiments provide fundamental information as well as insights into QCD dynamics• Experiments: polarized beams(e, p), polarized targets (p, d, 3He/n) longitudinal and transverse target polarization

A||, A|_ A1, A2

||, |_ Spin Structure Functions g1(x, Q2), g2(x, Q2) Role of unpolarized PDFs/ R• Polarized PDFs q(x)

LO, NLO,…, QCD evolution, Higher-twists

• Moments, sum rules• High-x, low-x • World data (CERN, SLAC, HERMES, RHIC-spin, JLab, …)• JLab 6 GeV: high-x, low Q2, high-precision. , • Future :12 GeV

Jefferson Lab Experimental Halls

HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS

6 GeV polarized CW electron beam Pol=85%, 200A

Will be upgraded to 12 GeV by ~2014

JLab Polarized Proton/Deuteron Target

• Polarized NH3/ND3 targets

• Dynamical Nuclear Polarization

• In-beam average polarization

70-90% for p

30-50% for d• Luminosity ~ 1035 (Hall C/A)

~ 1034 (Hall B)

JLab Polarized 3He Target

longitudinal, transverse and vertical

Luminosity=1036 (1/s) (highest in the world)

Record high pol ~ 60%

60%15 uA

6 GeV JLab12

CHL-2CHL-2

Upgrade magnets Upgrade magnets and power suppliesand power supplies

Enhance equipment in Enhance equipment in existing hallsexisting halls

add Hall D (and beam line)

Experimental Halls

• (new) Hall D: linear polarized photon beam, Selonoid detetcor GluoX collaboration: exotic meson spectroscopy gluon-quark hybrid, confinement

• Hall B: CLAS12 GPDs, TMDs, …

• Hall C: Super HMS + existing HMS Form factors, structure functions (A1n/d2n), …

• Hall A: Dedicated devices + existing spectrometers Super BigBite, SoLID, MOLLER SIDIS (transversity/TMDs), PVDIS, …

JLab Spin Experiments

• Results: Published and Preliminary/Upcoming• Spin in the valence (high-x) region• Spin (g1/g2) Moments: Spin Sum Rules, d2

• SSA in SIDIS: Transversity (n) • SSA in Inclusive Reaction

• On-going• g2

p at low Q2

• Future: 12 GeV• Inclusive: A1/d2,

• Semi-Inclusive: Transversity, Flavor-decomposition

• Reviews: S. Kuhn, J. P. Chen, E. Leader, Prog. Part. Nucl. Phys. 63, 1 (2009)

Valence Quark Spin Structure

A1 at high x and flavor decomposition

Why Are PDFs at High x Important?

• Valence quark dominance: simpler picture

-- direct comparison with nucleon structure models

SU(6) symmetry, broken SU(6), diquark• x 1 region amenable to pQCD analysis

-- hadron helicity conservation?

role of quark orbit angular momentum?

• Clean connection with QCD, via lattice moments (d2)

• Input for search for new physics at high energy collider

-- evolution: high x at low Q2 low x at high Q2

-- small uncertainties amplified

-- example: HERA ‘anomaly’ (1998)

World data for A1 World data for A1

Proton Neutron

JLab E99-117 Precision Measurement of A1

n at Large xSpokespersons: J. P. Chen, Z. Meziani, P. Souder; PhD Student: X. Zheng

• First precision A1n 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)

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 and pQCD PDF fits without HHC constraint

Inclusive Hall A and B and Semi-Inclusive Hermes

BBS

BBS+OAM

H. Avakian, S. Brodsky, A. Deur, and F. Yuan, PRL 99, 082001 (2007)

pQCD with Quark Orbital Angular Momentum

Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon

Preliminary A1(p) Results, Hall C SANE

Courteous of O. Rondon

Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky

Preliminary A1(3He) Results, Hall A E06-014

Courteous of D. Flay

Spin-Structure in Resonance Region: E01-012

Spokesperson: N. Liyanage, J. P. Chen, S. Choi; PhD Student: P. Solvignon PRL 101, 1825 02 (2008)

A13He (resonance vs DIS)1 resonance vs. pdfs

x Q2 x

A1p at 11 GeV (CLAS12)

Projections for JLab at 11 GeV

A1n at 11 GeV (Hall C/A)

u and d at JLab 11 GeV

Polarized Sea

JLab @11 GeV

multiplicities in SIDIS ep→e’X

DSS (Q2=2.5GeV2)

DSS (Q2=25GeV2)

CLAS 6Hall-C

Moments of Spin Structure Functions

Sum Rules, Polarizabilities

First Moment of g1p :1

p

EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)Spokespersons: V. Burkert, D. Crabb, G. Dodge,

1p

Total Quark Contribution to Proton Spin (at high Q2)

Twist expansion at intermediate Q2, LQCD, ChPT at low Q2

First Moment of g1n :1

n

E94-010, PRL 92 (2004) 022301 E97-110, preliminaryEG1a, from d-p

1n

1 of p-n

EG1b, PRD 78, 032001 (2008)E94-010 + EG1a: PRL 93 (2004) 212001

Second Spin Structure Function g2

Burkhardt - Cottingham Sum Ruled2: Color Lorentz Force (Polarizability)

Spin Polarizabilities

Precision Measurement of g2n(x,Q2): Search for Higher Twist Effects

• Measure higher twist quark-gluon correlations.• Hall A Collaboration, K. Kramer et al., PRL 95, 142002 (2005)

BC Sum Rule

P

N

3He

BC = Meas+low_x+Elastic

0<X<1 :Total Integral

very prelim

“low-x”: refers to unmeasured low x part of the integral. Assume Leading Twist Behaviour

Elastic: From well know FFs (<5%)

“Meas”: Measured x-range

Brawn: SLAC E155xRed: Hall C RSS Black: Hall A E94-010Green: Hall A E97-110 (preliminary)Blue: Hall A E01-012 (spokespersons: N. Liyanage, former student, JPC)(preliminary)

0)(1

0 22 dxxgΓ

BC Sum Rule

P

N

3He BC satisfied w/in errors for 3He

BC satisfied w/in errors for Neutron(But just barely in vicinity of Q2=1!)

BC satisfied w/in errors for JLab Proton2.8 violation seen in SLAC data

very prelim

Color Lorentz Force (Polarizability): d2

• 2nd moment of g2-g2WW

d2: twist-3 matrix element

d2 and g2-g2WW: clean access of higher twist (twist-3) effect: q-g correlations

Color polarizabilities are linear combination of d2 and f2

Provide a benchmark test of Lattice QCD at high Q2

Avoid issue of low-x extrapolation

Relation to Sivers and other TMDs

1

0

22

21

2

1

0

22

22

222

)],(3),(2[

)],(),([3)(

dxQxgQxgx

dxQxgQxgxQd WW

d2(Q2)

E08-027 “g2p”SANE

“d2n” new in Hall A

6 GeV Experiments

Sane: new in Hall C

“g2p” in Hall A, 2011

projected

Preliminary results on neutron from E01-012Spokespersons: J. P. Chen, S. Choi, N. Liyanage, plots by P. Solvignon

Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon

Preliminary A2(p) Results, Hall C SANE

Courteous of O. Rondon

Projection on d2p from Hall C SANE

Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky

Projection on Hall A E06-014 (d2n)

Courteous of D. Flay

E08-027 : Proton g2 Structure Function Fundamental spin observable has never been measured at low or moderate Q2

BC Sum Rule : violation suggested for proton at large Q2, but found satisfied for the neutron & 3He.

Spin Polarizability : Major failure (>8 of PT for neutron LT. Need g2 isospin separation to solve.

Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties.

Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from H Lamb shift.

BC

Su

m R

ule

Spokespersons: A. Camsonne, J. P. Chen, D. Crabb, K. Slifer, 6 PhD students

Scheduled to run 2/2012-5/2012

Sp

in P

ola

riza

bili

ty

LT

Spin Polarizabilities Preliminary E97-110 (and Published E94-010)

Spokesperson: J. P. Chen, A. Deur, F. Garibaldi, plots by V. Sulkosky • Significant disagreement between data and both ChPT calculations for LT

• Good agreement with MAID model predictions

0 LT

Q2

Q2

Single Target-Spin Asymmetries in SIDIS

Transversity/Tensor Charge

Transversity

• Three twist-2 quark distributions:• Momentum distributions: q(x,Q2) = q↑(x) + q↓(x)• Longitudinal spin distributions: Δq(x,Q2) = q↑(x) - q↓(x)• Transversity distributions: δq(x,Q2) = q┴(x) - q┬(x)

• It takes two chiral-odd objects to measure transversity• Semi-inclusive DIS

Chiral-odd distributions function (transversity) Chiral-odd fragmentation function (Collins function)

E06-010 3He Target Single-Spin Asymmetry in SIDISSpokespersons: J. P. Chen, E. Cisbani, H. Gao, X. Jiang, J-C. Peng, 7 PhD students

3He Sivers SSA:negative for π+,

3He Collins SSA small Non-zero at highest x for +

Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

X. Qian, et al. PRL (2011)

Results on Neutron

Collinsasymmetries are not large, except at x=0.34

Sivers negative

Blue band: model (fitting) uncertainties Red band: other systematic uncertainties

12 GeV: Mapping of Collins Asymmetries with SoLID

• Both + and -

• For one z bin

(0.4-0.45)

• Will obtain many z bins (0.3-0.7)

• Tensor charge

E12-10-006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. QianE12-11-007(p) , Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, Z-E. Mezinai

Summary

• Spin structure study full of surprises and puzzles• A decade of experiments from JLab: exciting results

• valence spin structure • precision measurements of g2/d2: high-twist • spin sum rules and polarizabilities• first neutron transversity

• Bright future• 12 GeV Upgrade will greatly enhance our capability

• Precision determination of the valence quark spin structureflavor separation

• Precision measurements of g2/d2

• Precision extraction of transversity/tensor charge