0 at Jefferson Lab - SNUq2c.snu.ac.kr/presentation_file/Pacific-Spin2009Choi.pdf · •...
Transcript of 0 at Jefferson Lab - SNUq2c.snu.ac.kr/presentation_file/Pacific-Spin2009Choi.pdf · •...
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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.
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QCD and Strong Interaction
• Accepted theory for
strong interaction
• Running coupling
constant ~ 1
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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
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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)
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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
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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
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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
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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
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Jefferson Lab
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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
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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)
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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)
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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
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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
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Longitudinal Spin
• Spin in valence (high x) region
• Moments of spin structure functions
• Spin sum rules
• Spin polarizabilities
• Quark-hadron duality
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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
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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
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Projections for JLab at 12 GeV
A1n
A1p
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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
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Bjorken Integral at Low Q2
EG1b, PRD 78, 032001 (2008)E94-010 + EG1a: PRL 93 (2004) 212001
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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)
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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)
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Higher Moments &Generalized Spin Polarizabilities
• generalized forward spin polarizability γ0
• generalized L-T spin polarizability δLT
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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
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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
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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
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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
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Transverse Spin (I)Inclusive
• g2 Structure Function and Moments
• Burkhardt-Cottingham Sum Rule
• Color Polarizability d2
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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
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Precision Measurement of g2n
• Measure higher twist → quark-gluon correlations.• Hall A Collaboration, K. Kramer et al., PRL 95, 142002 (2005)
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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
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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
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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?
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very prelimGREEN: E97-110. (Hall A, 3He)
RED : RSS. (Hall C, NH3,ND3)
BLUE: E01-012. (Hall A, 3He)
Proton
Neutron
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E08-027 “g2p”SANE
“d2n” completed in Hall A
6 GeV Experiments
Sane: completed in Hall C
“g2p” in Hall A, 2011
projected
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Transverse Spin (II)
• Single Spin Asymmetries in SIDIS
• Transversity and TMD’s
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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)
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Leading-Twist TMD’s
Quark
Nucleon
Unpol.
Long.
Trans.
Unpol. Long. Trans.
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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
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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
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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
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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)
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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-
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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
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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