The Spin Physics Program at Jefferson Lab Sebastian Kuhn Old Dominion University e e PtPt PePe

Overview Introduction: The Spin Physics Program at Jlab Results on moments: Sum rules, Q 2 -dependence Results on g 1 and A 1 : Resonances, quark spin distributions, duality Semi-inclusive and exclusive results Outlook - the future ( GeV)

The 2 dimensions of the structure of a spinning nucleon Inclusive  Exclusive Hadronic d.o.f  Quark d.o.f MomentsSSFs g 1, A 1 SIDISFully recon- structed FS OPE Duality  q, x->1 Orbital Angular Momentum Q 2 increases exclincl h q

Jefferson Lab A C B ≤6 GeV electron beam Longitudinal polarization up to 85% Beam current from 50µA CLAS

Hall A 2 HRS and pol. 3 He target

Hall B - CLAS Kinematic coverage of the data analyzed so far - new 2.5 and 4.2 GeV data are forthcoming drift chambers beam Cerenkov calorimeter e-e- NH 3, ND 3 Time of flight scintillators CLAS

Polarized 15 NH 3 / 15 ND 3 target Magnetic field ~ 5 Tesla Temperature ~ 1 K µWave driven DNP Four target cells: NH 3 ND 3 Empty (LHe) 12 C Also separate 15 N target

Hall C - RSS Q2Q2

Analysis - e.g. inclusive Asym. for CLAS Electron Identification Fiducial cuts Electromagnetic calorimeter cuts Cherenkov cut Vertex cut In an inclusive asymmetry analysis acceptance and detector efficiency cancel out N +/- Yield for electron/target spins antiparallel (+) or parallel (-) Q +/- Integrated beam charge Physics asymmetry A ||  P e Beam polarization  P t Target polarization  DF Dilution factor  C back Background processes pion contamination & pair symmetric

Analysis cont’d For Halls A and C: Measure both A || and A  to extract both A 1 and A 2 from data Unpolarized structure functions F 1, R from parametrizations of world data (in particular Hall C) Hall A measures directly cross section difference - can extract g 1,2 ( 3 He) directly without using these parametrizations

Moments of spin structure functions ChPT GDH sum rule DIS pQCD operator product expansion quark models Lattice QCD? Q 2 (GeV 2 ) 1 11 exclincl h q Related to matrix elements of local operators - in principle accessible to lattice QCD calculations Sum rules relate moments to the total spin carried by quarks in the nucleon and to axial vector coupling g A of the nucleon At high Q 2, can be expanded in a power series (higher twist, OPE) At low Q 2, amenable to Chiral Perturbation Theory Bjorken Sum Rule: Burkhardt-Cottingham Sum Rule Twist 3

Generalized GDH sum ; Relates photo-absorption cross sections to a macroscopic (“hadronic”) feature of the proton (or any spinning system) ChPT GDH sum rule DIS pQCD operator product expansion quark models Lattice QCD? Q 2 (GeV 2 ) 1 11 Can be extended to Q 2 ≠ 0 Connects to  1 = ∫ g 1 (x)dx at high Q 2 exclincl h q

Q 2 -dependence of  1 exclincl h q DeuteronProton

Q 2 -dependence of  1 Proton - Neutron f 2 p-n = -0.18…0.02 exclincl h q Hall B prelim. Neutron

Integral d 2 - a measure of higher twist Proton exclincl h q Neutron BCSR

Low Q 2 -dependence of  1 Proton exclincl h q  PT I(Q 2 ) (  b) GDH Sum Rule Slope constrained by GDH Sum Rule Neutron

Double Spin Asymmetries at low W - a measure of the spin structure of excited resonances exclincl h q Data from CLAS - Proton 1.6 GeV Data from RSS - Proton Q 2 = 1.3 GeV 2

Double Spin Asymmetry A 1 at higher W Information of the helicity carried by the quarks inside a spinning nucleon. DIS data from CLAS - Proton DIS data from CLAS - Deuteron exclincl h q

Double Spin Asymmetry A 1 at higher W … can be properly extracted from NLO (DGLAP) analyses of A 1 (x,Q 2 ) ≈ g 1 /F 1 (x,Q 2 ) …  Extract polarized PDFs at large x (…just an indication of the precision that should be possible with the new data) exclincl h q Hall B prelim. DIS data from Hall A - Neutron Jlab/HallA

Ultimately: NLO analysis of data from p, n and d Example: Statistics on g 1p from CLAS. Similar statistics on the deuteron. Plenty more data from RSS, plus data on 3 He from Hall A. exclincl h q Q 2 =0.05 Q 2 =4.2

Structure function g 2n from Hall A exclincl h q DISResonance Region

Quark-Hadron Duality CLAS result for g 1p exclincl h q Hall A RSS

Quark-Hadron Duality - Partial Integrals exclincl h q  S   F   Global  S   F   Global ProtonDeuteron

SIDIS - flavor tagging Good agreement with HERMES  + data at 3x higher Q 2 x-dependence follows PEPSI (Lund) Monte Carlo using GRSV polarized PDFs (LO) exclincl h q

SIDIS - flavor tagging g 1 /F 1 inclusive, for the sum of     , and for   are consistent with each other in the range 0.4<z<0.7, as expected in LO with factorization and current fragmentation dominance. No significant z- dependence seen 0.3<z<0.7, as well as only weak p T - dependence. exclincl h q

SIDIS - SSA results Twist-2Higher Twist Data in rough agreement with Efremov et al. predictions, except for  0 sin(  ) term (evidence for terms not involving Collins fragmentation?) incl h q excl

Exclusive π 0 production in the resonance region A et AtAt  S 11 /D < Q 2 < o <  * < -108 o Data also on , π +, π -,  incl h q excl

DVCS Target single spin asymmetry for p(e,e’p  ) Mostly sensitive to the GPD “H” which is related to  q and axial form factor E beam = 5.7 GeV Q 2 > 1 GeV 2, W > 2 GeV A UL = (0.210±0.053)sin  Dashed curve following M. Vanderhaeghen ~ incl h q excl

The Future with ≤ 6 GeV Low Q 2 extended GDH Sum Rule in Hall A using Septum magnets and low beam energies exclincl h q

Low Q 2 extended GDH Sum Rule with CLAS using new Cherenkov Detector exclincl h q p d

Further plans w/ 6 GeV - CLAS CLAS with Inner Calorimeter SIDIS DVCS… 424 PbWO4 ……..crystals IC at CLAS opens new avenue for studies of spin and azimuthal asymmetries of exclusive and semi-inclusive     CLAS CLAS+IC exclincl h q

Further plans w/ ≤6 GeV - Hall A Experiment E Use “Bigbite” Spectrometer Main focus: g 2 exclincl h q

Further plans w/ ≤6 GeV - Hall C Spin Asymmetries of the Nucleon Experiment (SANE) New Spectrometer (BETA) with large calorimeter and Cher. counter Main focus: g 2 Possible Extension: “Semi-SANE”… exclincl h q

The Future with 12 GeV - A 1 exclincl h q

The Future with 12 GeV - A 1 exclincl h q Expected Precision in  d/d …and other PDFs, more precise determination of sum rules,...

The Future with 12 GeV - SIDIS exclincl h q PDFs from flavor tagging… …and many more observables: Single spin asymmetries, transversity, Sivers and Boer/Mulders functions, DVCS, …  Higher twist, quark orbital angular momentum, “proton tomography”…

Conclusion A very precise data set on A 1, A 2, g 1 and g 2 covering a large kinematic range in x and Q 2 has been collected at Jefferson Lab. Several analyses are completed and have been published. Several data sets are still under analysis. Future experiments (both planned and already approved) using up to 6 GeV beam energy will continue to study the spin structure of the nucleon. A truly exciting program lies ahead of us with the 12 GeV electron beam at Jefferson Lab.