Transcript Chen
Spin Structure with JLab 6 and 12 GeV
J. P. Chen, Jefferson Lab INT-12-49W: Workshop on Orbital Angular Momentum in QCD, Feb. 6, 2011 Overview Selected Results from JLab 6 GeV A 1 at High-x: Valence Quark Spin Distributions Moments g 2 /d 2 : 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, 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, Higher-twists Moments, sum rules High-x, low-x World data (CERN, SLAC, HERMES, RHIC spin, JLab, …) JLab 6 GeV: high-
x
, low
Q 2
, high-precision.
,
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 • In-beam average polarization 70-90% for p 30-50% 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%
CHL-2 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 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 (g 1 /g 2 ) Moments: Spin Sum Rules, d 2 • SSA in SIDIS: Transversity (n) • SSA in Inclusive Reaction • On-going • g 2 p at low
Q 2
• Future: 12 GeV • Inclusive: A 1 /d 2, • Semi-Inclusive: Transversity, Flavor-decomposition • 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 E99-117
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 Semi-Inclusive 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 E06-014
Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky
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) 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
Hall-C 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
E94-010, PRL 92 (2004) 022301
E97-110, preliminary
EG1a, from
d-p
EG1b, PRD 78, 032001 (2008) E94-010 + EG1a: PRL 93 (2004) 212001 G
1
of p-n
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 quark-gluon 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 E94-010 Green: Hall A E97-110 (preliminary) Blue: Hall A E01-012 (spokespersons: N. Liyanage, former student, JPC) (preliminary) BC = Meas+low_ x +Elastic “Meas”: Measured x-range “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 2 • 2 nd moment of g 2 -g 2 WW d 2 : twist-3 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 (twist-3) effect: Color polarizabilities c E ,c B are linear combination of d 2 and f 2 q-g 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 Spokespersons: J. P. Chen, S. Choi, N. Liyanage, plots by P. Solvignon 2 Spokespersons: S. Choi, M. Jones, Z. Meziani and O. Rondon Courteous of O. Rondon 2 n Spokespersons: S. Choi, Z. Meziani, X. Jiang and B. Sawasky Courteous of D. Flay E08-027 : 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 2/2012-5/2012 • • 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 d LT Good agreement with MAID model predictions g 0 d LT Q 2 Q 2 Single Target-Spin Asymmetries in SIDIS Transversity • Three twist-2 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 chiral-odd objects to measure transversity • Semi-inclusive DIS Chiral-odd distributions function (transversity) Chiral-odd fragmentation function (Collins function) E06-010 3 Spokespersons: J. P. Chen, E. Cisbani, H. Gao, X. Jiang, J-C. Peng, 7 PhD students 3 He ( e , e ' h ), h = p + , p - X. Qian, et al. PRL (2011) 3 He Collins SSA small Non-zero at highest x for p + 3 He Sivers SSA: negative for π +, Blue band : model (fitting) uncertainties Red band : other systematic uncertainties 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 E12-10-006 3He(n), Spokespersons: J. P. Chen, H. Gao, X. Jiang, J-C. Peng, X. Qian E12-11-007(p) , Spokespersons: K. Allda, J. P. Chen, H. Gao, X. Li, Z-E. Mezinai • Both p + and p • For one z bin (0.4-0.45) • Will obtain many z bins (0.3-0.7) • Tensor charge • 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 : high-twist • 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 chargeColor Lorentz Force (Polarizability): d
Preliminary results on neutron from E01-012
Preliminary A
(p) Results, Hall C SANE
Projection on d2p from Hall C SANE
Projection on Hall A E06-014 (d
)
Transversity/Tensor Charge
He Target Single-Spin Asymmetry in SIDIS
Results on Neutron
Summary