Spin Physicsat Jefferson Lab

Seonho ChoiSeoul National University

Pacific-Spin 2009, Yamagata, JapanSeptember 15, 2009

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Overview

• Introduction to spin physics at Jefferson Lab

• Longitudinal and transverse spin

• Selected results from Jefferson Lab

• Recent measurements

• Plan after 12 GeV upgrade

Most of the slides have been graciously offered by many colleagues from Halls A, B and C with special thanks to Dr. Jian-Ping Chen.

QCD and Strong Interaction

• Accepted theory for

strong interaction

• Running coupling

constant ~ 1

QCD and Strong Interaction

• Asymptotic freedom at high energy: perturbative calculation

• Significant interaction at intermediate energy: quark-gluon correlations

• Strong interaction at low energy : confinement

• Theoretical tools: pQCD, OPE, Lattice QCD, ChPT etc

• A major challenge in fundamental physics

• Understand QCD in strong interaction region (at low energy)

• Study and understand nucleon structure

Nucleon Structureand Sum Rules

• 3 valence quarks carry ~50% of the nucleon momentum

• Spin=1/2, quarks contribute ~30% Spin Sum Rule

• Large anomalous moment GDH Sum Rule

• Axial charge Bjorken Sum Rule

• Angular momentum Generalized Parton Distributions

• Polarizabilities (spin & color)

Three Decadesof Spin Structures

• 1980’s: EMC (CERN) + early SLAC

• quark contribution to proton is very small - spin crisis

• Violation of Ellis-Jaffe Sum Rule

Three Decadesof Spin Structures

• 1990’s: SLAC, SMC(CERN), HERMES(DESY)

• the rest = gluon and quark orbital angular momentum

• Bjorken Sum Rule verified to <10% level

Three Decadesof Spin Structures

• 2000’s: COMPASS(CERN), HERMES, RHIC-Spin, JLab, ...

•

• probably small

• Orbital angular momentum probably significant

• Transversity

• Transverse-momentum dependent distributions

• Generalized Parton Distributions

Much more work to do at next decade

Jefferson Labat a Glance

• Electron linear accelerator

• Beam energy up to ~ 6 GeV

• Beam polarization over 80%

• Strained GaAs crystal + laser

• 100% duty cycle, continuous beam

• 3 Experimental Halls: A, B and C

Jefferson Lab

Jefferson Lab

An aerial view of the recirculating linear accelerator and 3

experimental halls.

Cryomodules in the accelerator tunnel

Superconducting radiofrequency (SRF) cavities undergo vertical testing.

CEBAF Large Acceptance Spectrometer (CLAS) in Hall B

Polarized 3He Target

• Arbitrary polarization direction (longitudinal, transverse or vertical)

• Luminosity: 1036 cm-2s-1

• In-beam polarization: > 65%

• Effective polarized neutron target

• 13 completed experiments

• 6 approved with 12 GeV (Halls A,C)

Polarized H/D Target

• Polarized NH3/ND3 targets

• Dynamical nuclear polarization

• In-beam polarization

• 70-90% for p

• 30-40% for d

• Luminosity

• 1035 (Hall C), 1034 (Hall B)

JLab Spin Experiments

• Results

• Moments: spin sum rules and polarizabilities

• Higher twists: g2/d2

• Quark-hadron duality

• Spin in the valence (high x) region

• Just completed

• d2p and d2n

• Transversity on the neutron target

JLab Spin Experiments

• Planned

• g2p at low Q2

• CLAS with polarized H/D target

• Future at 12 GeV

• Inclusive: A1, d2

• Semi-Inclusive

• Transversity, TMD’s, Flavor-decomposition

Longitudinal Spin

• Spin in valence (high x) region

• Moments of spin structure functions

• Spin sum rules

• Spin polarizabilities

• Quark-hadron duality

Valence A1p and A1n

Hall B CLAS, Phys.Lett. B641 (2006) 11 Hall A E99-117, PRL 92, 012004 (2004) PRC 70, 065207 (2004)

A1nA1p

pQCD with LqInclusive Hall A and B and Semi-Inclusive Hermes

BBS

BBS+OAM

F. Yuan, H. Avakian, S. Brodsky, and A. Deur, arXiv:0705.1553

Projections for JLab at 12 GeV

A1n

A1p

First Moments of g1p and g1n

EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)

E94-010, from 3He, PRL 92 (2004) 022301 E97-110, from 3He, EG1a, from d-p

Test fundamental understanding

ChPT at low Q2, Twist expansion at high Q2, Future Lattice QCD

Bjorken Integral at Low Q2

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

Effective Coupling Extracted from Bjorken Integral

A. Deur, V. Burkert, J. P. Chen and W. Korsch PLB 650, 244 (2007) and PLB 665, 349 (2008)

Duality in Spin StructureDuality in Spin-Structure: Hall A E01-012 Results

! g1/g2 and A1/A2 (3He/n) in resonance region,

1 < Q2 < 4 GeV2

! Study quark-hadron duality in spin structure.

<Resonances> = <DIS> ?

! PRL 101, 1825 02 (2008)

!1 resonance comparison with pdfs

• g1/g2 and A1/A2 (3He/n) in resonance region,

1 < Q2 < 4 GeV2

• Study quark-hadron duality in spin structure.

<Resonances> = <DIS> ?

• PRL 101, 182502 (2008)

Higher Moments &Generalized Spin Polarizabilities

• generalized forward spin polarizability γ0

• generalized L-T spin polarizability δLT

Neutron Spin Polarizabilities• δLT insensitive to Δ resonance

• RB ChPT calculation with resonance for γ0 agree with data at Q2=0.1 GeV2

• Significant disagreement between data and both ChPT calculations for δLT

• Good agreement with MAID model predictions

E94-010, PRL 93 (2004) 152301

Spin Polarizabilitiesfrom Hall B

• EG1b, Prok et al. arXiv:0802.2232

• Large discrepancies with ChPT!• Only longitudinal data, model for

transverse (g2)

• γ0 sensitive to resonance

Comparison with ChPT IAn Γ1

P Γ1n Γ1

p-n γ0p γ0

n δLTn

Q2 (GeV2) 0.1 0.1 0.05 0.1 0.05 0.16 0.05 0.05 0.1 0.1

HBχPT poor poor good poor good good good bad poor bad

RBχPT/Δ good fair fair fair good poor fair bad good bad

δLT puzzle: δLT not sensitive to Δ, one of the best quantities to test χPT,

it disagrees with neither calculations by several hundred %!

A challenge to χPT theorists.

Very low Q2 data g1/g2 on n(3He) (E97-110)

g1 on p and d available soon (EG4)

Recently approved: g2 on proton E08-027

New Experiment onProton g2 and δLT

g2 : central to knowledge of Nucleon Structure but remains unmeasured at low Q2 — Critical input to Hydrogen Hyperfine Calculations— Violation of BC Sum Rule suggested at large Q2

— State-of-the-Art χPT calcs fail dramatically for δLT

Transverse Spin (I)Inclusive

• g2 Structure Function and Moments

• Burkhardt-Cottingham Sum Rule

• Color Polarizability d2

Spin Structure Function g2• Experiments: transversely polarized target SLAC E155x, (p/d) JLab Hall A (n), Hall C (p/d)

• g2 leading twist related to g1 by Wandzura-Wilczek relation

• g2 - g2WW: a clean way to access twist-3 contribution

quantify q-g correlations

Precision Measurement of g2n

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

Burkhardt-Cottingham Sum Rule

Brawn: SLAC E155xRed: Hall C RSS Black: Hall A E94-010Green: Hall A E97-110 (preliminary)Blue: Hall A E01-012(very preliminary)

p

3He

n

SLAC

Burkhardt-Cottingham Sum Rule

p

3He

n

BC satisfied within errors for 3He

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

BC satisfied within errors for JLab Proton2.8σ violation seen in SLAC data

SLAC

Color Polarizability d2• 2nd moment of g2-g2

WW

d2: twist-3 matrix element

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

Color polarizabilities χΕ,χΒ 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?

very prelimGREEN: E97-110. (Hall A, 3He)

RED : RSS. (Hall C, NH3,ND3)

BLUE: E01-012. (Hall A, 3He)

Proton

Neutron

E08-027 “g2p”SANE

“d2n” completed in Hall A

6 GeV Experiments

Sane: completed in Hall C

“g2p” in Hall A, 2011

projected

Transverse Spin (II)

• Single Spin Asymmetries in SIDIS

• Transversity and TMD’s

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 make transversity detectable

• Semi-inclusive DIS

Chiral-odd distributions function (Transversity)

Chiral-odd fragmentation function (Collins function)

• TMDs: (without integrating over PT)

• Distribution functions depends on x, k┴ and Q2 : δq, f1T┴ (x,k┴ ,Q2), …

• Fragmentation functions depends on z, p┴ and Q2 : D, H1(x,p┴ ,Q2)

• Measured asymmetries depends on x, z, P┴ and Q2 : Collins, Sivers, …

(k┴, p┴ and P┴ are related)

Leading-Twist TMD’s

Quark

Nucleon

Unpol.

Long.

Trans.

Unpol. Long. Trans.

E06-010 Single Target-Spin Asymmetry in Semi-Inclusive n↑(e,e′π+/-) Reaction on a Transversely Polarized 3He Target

Collins

Sivers

First neutron measurement

7 PhD Students

Completed data taking 10/08-2/09

exceeded PAC approved goal

Hall-A Transversity: en→e’πXen→e’ΚX

Polarized 3He: effective polarized neutron targetWorld highest polarized luminosity: 1036

New record in polarization: >70% without beam ~65% in beam and with spin-flip (proposal 42%)

HRSL for hadrons (π± and K±), new RICH commissioned

BigBite for electrons, 64 msr, detectors performing well

A1 PT-dependence in SIDIS (CLAS6) (Harut Avagyan)

M.Anselmino et al hep-ph/0608048

• PT-dependence of A1 provides access to kT-distributions and widths of f1 and g1

• Data shows slight preference for μ0< μ2

x10 more data is already accumulated in 2009!

μ02=0.25GeV2

μD2=0.2GeV2

0.4<z<0.7

Measurement of Sivers function and GPD-E at CLAS 6

DVCS Transverse asymmetry (function of momentum transfer to proton) is large and has

strong sensitivity to GPD-E

CLAS will provide a measurements of Sivers asymmetry at large x, where the effect is large and models unconstrained by previous measurements.

Meissner, Metz & Goeke (2007)

GPD-E=0

CLAS6 (25 days-2011)(DVCS) (SIDIS)

3-D Mapping of Collins/Sivers Asymmetries at JLab 12 GeVWith A Large Acceptance Solenoid Detector

• Both π+ and π-

• For one z bin (0.5-0.6)

• Will obtain 4 z bins (0.3-0.7)

• Upgraded PID for K+

and K-

Summary

• Spin structure study is full of surprises and puzzles

• A decade of experiments from JLab: exciting results

• valence spin structure, quark-hadron duality

• spin sum rules and polarizabilities

• test χPT calculations, →‘δLT puzzle’

• precision measurements of g2/d2: higher-twist

• first neutron transversity measurement

Summary (cont.)

• JLab played a major role in recent experimental efforts

• shed light on our understanding of STRONG QCD

• lead to breakthrough?

• Bright future

• complete a chapter in spin structure study with 6 GeV JLab

• 12 GeV Upgrade will greatly enhance our capability

• Goal: a full understanding of nucleon structure and strong interaction