Transcript Chen
Spin Structure with JLab 6 and 12 GeV
J. P. Chen, Jefferson Lab INT1249W: Workshop on Orbital Angular Momentum in QCD, Feb. 6, 2011 Overview Selected Results from JLab 6 GeV A 1 at Highx: Valence Quark Spin Distributions Moments g 2 /d 2 : BC 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, 3 He/n) longitudinal and transverse target polarization
A, A
_ Ds
,
Ds
_
A 1 , A 2
Spin Structure Functions g 1 (
x, Q 2
), g 2 (
x, Q 2
) Role of unpolarized PDFs/
R
Polarized PDFs D
q(x)
LO, NLO,…, QCD evolution, Highertwists Moments, sum rules Highx, lowx World data (CERN, SLAC, HERMES, RHIC spin, JLab, …) JLab 6 GeV: high
x
, low
Q 2
, highprecision.
,
Future : 12 GeV
Jefferson Lab Experimental Halls 6 GeV polarized CW electron beam Pol=85%, 200
m
A Will be upgraded to 12 GeV by ~2014 HallA: two HRS’ Hall B:CLAS Hall C: HMS+SOS
JLab Polarized Proton/Deuteron Target
• Polarized NH 3 /ND 3 targets • Dynamical Nuclear Polarization • Inbeam average polarization 7090% for p 3050% for d • Luminosity ~ 10 35 (Hall C/A) ~ 10 34 (Hall B)
60% 15 uA JLab Polarized 3 He Target
longitudinal, transverse and vertical
Luminosity= 10 36 (1/s) (highest in the world)
Record high pol ~ 60%
CHL2 Enhance equipment in existing halls add Hall D (and beam line) Upgrade magnets and power supplies
Experimental Halls
• • • •
(new) Hall D: linear polarized photon beam, Selonoid detetcor

GluoX
collaboration: exotic meson spectroscopy gluonquark 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 (g 1 /g 2 ) Moments: Spin Sum Rules, d 2 • SSA in SIDIS: Transversity (n) • SSA in Inclusive Reaction • Ongoing • g 2 p at low
Q 2
• Future: 12 GeV • Inclusive: A 1 /d 2, • SemiInclusive: Transversity, Flavordecomposition • Reviews: S. Kuhn, J. P. Chen, E. Leader, Prog. Part. Nucl. Phys. 63, 1 (2009)
Valence Quark Spin Structure
A 1
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 (d 2 ) • Input for search for new physics at high energy collider  evolution: high x at low Q 2 low x at high Q 2  small uncertainties amplified  example: HERA ‘anomaly’ (1998)
Proton
World data for A
1 Neutron
JLab E99117
Precision Measurement of A
1 n
at Large x
Spokespersons: J. P. Chen, Z. Meziani, P. Souder; PhD Student: X. Zheng
• • • • • • • First precision
A 1 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)
Polarized Quark Distributions
• Combining
A 1 n
and
A 1 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
pQCD with Quark Orbital Angular Momentum
H. Avakian, S. Brodsky, A. Deur, and F. Yuan , PRL 99, 082001 (2007) Inclusive Hall A and B and SemiInclusive Hermes BBS BBS+OAM
Preliminary A
1
(p) Results, Hall C SANE
Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon
Courteous of O. Rondon
Preliminary A
1
(
3
He) Results, Hall A E06014
Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky
Courteous of D. Flay
SpinStructure in Resonance Region: E01012
Spokesperson :
N. Liyanage
,
J. P. Chen, S. Choi;
PhD Student:
P. Solvignon
PRL 101, 1825 02 (2008) G
1 resonance vs. pdfs A 1 3He (resonance vs DIS) x Q 2
x
Projections for JLab at 11 GeV
A 1 n at 11 GeV (Hall C/A) A 1 p at 11 GeV (CLAS12)
D u and D d at JLab 11 GeV Polarized Sea
JLab @11 GeV
p
multiplicities in SIDIS
HallC ep →e’ p X CLAS 6
DSS (Q 2 =25GeV 2 ) DSS (Q 2 =2.5GeV
2 )
Moments of Spin Structure Functions Sum Rules, Polarizabilities
First Moment of g
1 p
:
G
1 p
Total Quark Contribution to Proton Spin (at high Q 2 ) Twist expansion at intermediate Q 2 , LQCD, ChPT at low Q 2 G
1 p EG1b, arXiv:0802.2232 EG1a, PRL 91, 222002 (2003)
Spokespersons: V. Burkert, D. Crabb, G. Dodge,
First Moment of g
1 n
:
G
1 n
G
1 n
E94010, PRL 92 (2004) 022301
E97110, preliminary
EG1a, from
dp
EG1b, PRD 78, 032001 (2008) E94010 + EG1a: PRL 93 (2004) 212001 G
1
of pn
Second Spin Structure Function g 2 Burkhardt  Cottingham Sum Rule d 2 : Color Lorentz Force (Polarizability) Spin Polarizabilities
Precision Measurement of
g 2 n
(
x
,
Q 2
): Search for Higher Twist Effects • • Measure higher twist quarkgluon correlations .
Hall A Collaboration, K. Kramer
et al.
, PRL 95, 142002 (2005)
P N 3 He 0
BC Sum Rule
Γ 2 0 1
g
2 (
x
)
dx
0 Brawn: SLAC E155x Red: Hall C RSS Black: Hall A E94010 Green: Hall A E97110 (preliminary) Blue: Hall A E01012 (spokespersons: N. Liyanage, former student, JPC) (preliminary) BC = Meas+low_
x
+Elastic “Meas”: Measured xrange “low
x
”: refers to unmeasured low x part of the integral. Assume Leading Twist Behaviour Elastic : From well know FFs (<5%)
P N 3 He
BC Sum Rule
BC satisfied w/in errors for JLab Proton 2.8
s violation seen in SLAC data BC satisfied w/in errors for Neutron (But just barely in vicinity of Q 2 =1!) BC satisfied w/in errors for 3 He
Color Lorentz Force (Polarizability): d
2
• 2 nd moment of
g 2 g 2 WW d 2
: twist3 matrix element
d
2 (
Q
2 ) 3 0 1
x
2 [
g
2 (
x
,
Q
2 )
g
2
W W
(
x
,
Q
2 )]
dx
0 1
x
2 [ 2
g
1 (
x
,
Q
2 ) 3
g
2 (
x
,
Q
2 )]
dx d 2
and
g 2 g 2 WW
: clean access of higher twist (twist3) effect: Color polarizabilities c E ,c B are linear combination of
d 2
and
f 2 qg
correlations Provide a benchmark test of Lattice QCD at high
Q 2
Avoid issue of low
x
extrapolation Relation to Sivers and other TMDs
E08 027 “g2p” projected
d 2 (Q 2 )
SANE 6 GeV Experiments Sane : new in Hall C “g2p” in Hall A, 2011 “d2n” new in Hall A
Preliminary results on neutron from E01012
Spokespersons: J. P. Chen, S. Choi, N. Liyanage, plots by P. Solvignon
Preliminary A
2
(p) Results, Hall C SANE
Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon
Courteous of O. Rondon
Projection on d2p from Hall C SANE
Projection on Hall A E06014 (d
2 n
)
Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky
Courteous of D. Flay
E08027 : Proton g 2 Structure Function Fundamental spin observable has never been measured at low or moderate Q 2
Spokespersons: A. Camsonne, J. P. Chen, D. Crabb, K. Slifer, 6 PhD students BC Sum Rule :
violation suggested for proton at large Q 2 , but found satisfied for the neutron & 3 He.
Spin Polarizability
: Major failure (>8 s) of c PT for neutron d LT . Need g 2 isospin separation to solve.
Hydrogen HyperFine Splitting
: Lack of knowledge of g 2 at low Q 2 is one of the leading uncertainties.
Proton Charge Radius :
also one of the leading uncertainties in extraction of
Scheduled to run 2/20125/2012
• •
Spin Polarizabilities Preliminary E97110 (and Published E94010) Spokesperson: J. P. Chen, A. Deur, F. Garibaldi, plots by V. Sulkosky
Significant disagreement between data and both ChPT calculations for d LT Good agreement with MAID model predictions g
0
d
LT Q 2 Q 2
Single TargetSpin Asymmetries in SIDIS
Transversity/Tensor Charge
Transversity
• Three twist2 quark distributions: • Momentum distributions:
q(x,Q 2 ) = q ↑ (x) + q ↓ (x)
• Longitudinal spin distributions:
Δq(x,Q 2 ) = q ↑ (x)  q ↓ (x)
• Transversity distributions:
δq(x,Q 2 ) = q ┴ (x)  q ┬ (x)
• It takes two chiralodd objects to measure transversity • Semiinclusive DIS Chiralodd distributions function (transversity) Chiralodd fragmentation function (Collins function)
E06010
3
He Target SingleSpin Asymmetry in SIDIS
Spokespersons: J. P. Chen, E. Cisbani, H. Gao, X. Jiang, JC. Peng, 7 PhD students
3 He (
e
,
e
'
h
),
h
= p + , p 
X. Qian, et al.
PRL (2011)
3 He Collins SSA small Nonzero at highest x for
p
+ 3 He Sivers SSA: negative for π +, Blue band
: model (fitting) uncertainties
Red band
: other systematic uncertainties
Results on Neutron
Collins
asymmetries are not large, except at x=0.34
Sivers
p + (
ud
) negative
Blue band
: model (fitting) uncertainties
Red band
: other systematic uncertainties
12 GeV: Mapping of Collins Asymmetries with SoLID E1210006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, JC. Peng, X. Qian E1211007(p) , Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, ZE. Mezinai
• Both p + and p • For one z bin (0.40.45) • Will obtain many z bins (0.30.7) • Tensor charge
Summary
• Spin structure study full of surprises and puzzles • A decade of experiments from JLab: exciting results • valence spin structure • precision measurements of g • first neutron transversity 2 /d 2 : hightwist • spin sum rules and polarizabilities • Bright future • 12 GeV Upgrade will greatly enhance our capability • Precision determination of the valence quark spin structure flavor separation • Precision measurements of g 2 /d 2 • Precision extraction of transversity/tensor charge