Target Single Spin Asymmetries in 3 He(e,e’) Nucleon and Nuclear structure studies using two photon exchange with a vertically polarized 3 He target. Program Goal: Measure the “vertical” target single spin asymmetry A y in: Todd Averett, College of William and Mary Williamsburg, VA On behalf of the Jefferson Lab Hall A and polarized 3 He collaborations 7/1/131 Graduate Students: Yawei Zhang, Joe Katich, Xin Qian, Ellie Long quasi-elastic 3 He(e,e’) deep-inelastic 3 He(e,e’) quasi-elastic 3 He(e,e’n)

Born scattering and beyond Irritating correction to favorite diagram. Suppressed by α em relative to Born diagram 7/1/132 Jefferson Lab nuclear physicists’ favorite diagram (required for every talk): Born scattering Unpolarized elastic scattering

Born scattering and beyond How is it useful? Loop integral contains entire nucleon response. How do we observe this? 7/1/133 Dominates unpolarized and most polarized N(e,e’) scattering.

Two Photon Physics Topic 1: Elastic N(e,e’) scattering with two photon exchange: h = electron helicity, λ N (λ’ N ) = nucleon helicity, K=(k+k’)/2, P=(p+p’)/2 The functions are complex and reduce to the usual (real) structure functions and form factors in 1γ exchange: 7/1/134 A. Afanasev et al., Phys.Rev.D72:013008, 2005

Elastic form factor data Disagreement between recoil polarization and Rosenbluth separation measurements of proton form factors: two- photon exchange? Depends on the real part of the interference: 7/1/135 A.J.R. Puckett, Phys.Rev. C85 (2012) A. Afanasev et al., Phys.Rev.D72:013008, 2005 Born TPEX

At large Q 2, assume dominated by interaction with a single quark 7/1/136 At low Q 2, entire nucleon is involved 2-photon exchange calculations A. Afanasev et al., Phys.Rev.D72:013008, 2005 Elastic contribution to complex structure functions well known. Inelastic contribution estimated using e.g. form factors, resonance contributions, moments of GPD’s, ….

7/1/137 pQCD Calculation of TPE corrections to elastic form-factor data D. Borisyuk, A. Kobushkin, Phys.Rev. D79 (2009) Delta-resonance Contribution to Elastic TPE Partonic Approach S. Kondratyuk et al., Phys.Rev.Lett. 95 (2005) Hadronic Approach Examples of models

Jefferson Lab G E p /G M p vs. Q 2 7/1/138 Blunden et al. Phys. Rev. C72 (2005) A. Afanasev et al., Phys.Rev.D72:013008, 2005 GPD model Hadronic model

Unpolarized e - beam incident on 3 He target polarized normal to the electron scattering plane Note that unpolarized eN scattering, and double spin asymmetries (DSA) with beam and target polarization in-plane are dominated by 1-photon exchange. e.g. measurements of G E n, G M n, F 1, F 2, g 1, g 2 <----(Born approximation) However, A y =0 at Born level,  sensitive to physics at order α 3 ; two-photon exchange. Target Single Spin Asymmetry (SSA) 3 He θ e-e- 7/1/139

Target Single Spin Asymmetry 7/1/1310 A. DeRujula et al., Nuc. Phys. B35 (1971) 365 Absorptive part  Imaginary contribution N. Christ-T.D.-Lee, Phys. Rev. 143 (1966) 1310 For inclusive scattering N(e,e’), When we allow 2-photon exchange, the leading contribution is from 1γ + 2γ interference Measurement of A y versus Q 2 provides new constraints on nucleon models Useful check on GPD-model correction to elastic form factor data. Time reversal invariance, parity conservation, and the hermiticity of the electromagnetic current operator

7/1/1311 Existing A y QE data Expect A y ~ -1.5% at Q 2 =1 GeV 2

12 TPEX in Target SSA Target Single Spin Asymmetry (SSA)  Unpolarized electrons scattering from nucleons or nuclei polarized perpendicular to the incident electron helicity. Target spin vector at angle ϕ S relative to electron scattering plane Imaginary part The Target SSA ( ϕ S = π/2 ) for elastic scattering is: -- A y is zero for 1-photon exchange -- Leading contribution is 1 x 2 photon exchange -- Direct access to details of TPEX formalism and models -- New technique for studying nucleon substructure 7/1/13 Trento Convention A. Afanasev et al., Phys.Rev.D72:013008, 2005

7/1/1313

GPD-based model prediction 7/1/1314 Elastic Contribution Known Inelastic Contribution calculated from GPD parameterization o Neutron Dominated by G M n Predicted asymmetry at Q 2 =1 GeV 2 Uses the same formalism, GPD moments, as those used for elastic form-factor corrections. A. Afanasev et al., Phys.Rev.D72:013008, 2005

Experimental Design 7/1/1315 Use two symmetric, independent spectrometers for singles electron detection. Jefferson Lab Hall A HRS spectrometers uA beam Luminosity ~ /cm 2 /s Energy GeV

16 Hall A Polarized 3 He Target -- New vertically polarized 3 He target was constructed Top view, Jefferson Lab 3-axis polarized target Side view, Jefferson Lab vertical coils with target cell Polarization vs. time (arb.) 7/1/13

Hall A polarized 3 He target Effective polarized neutron target Spin Exchange Optical Pumping (SEOP) technology. Polarized alkali atoms exchange spin with 3 He nucleus during collisions 5:1 ratio of K:Rb at 235 o C Spectrally narrowed diode lasers 7/1/1317 Glass target cell

Events Selection 7/1/1318 Cherenkov ADC spectrum EM calorimeter ADC Pre-shower vs. shower Reconstructed interaction position in glass target cell

19 New Results for A y QE -- Q 2 dependence in the quasi-elastic single spin asymmetry, A y -- Agrees with GPD model ** at Q 2 = 1.0 GeV Asymmetry stays large at low Q 2: WHY??? -- TPEX important at low Q 2, -relevant for G E p /G M p at low Q 2 ?? 3He3He neutron GPD calculation 7/1/13

Topic 2: What about A y for n(e,e’) in DIS? The formalism remains the same: A y =0 for 1-photon exchange For DIS, one assumes that the scattering is dominated by two photon exchange with a single quark. Scattering from a single quark in the naïve QPM gives A y =0 at all orders in α A y ≠ 0 arises from e.g. quark mass, gluon exchange (higher- twist effects) 7/1/1320 A y in deep-inelastic scattering Naïve QPM

7/1/1321 Taken From: A. Metz, INT Workshop on Orbital Angular Momentum in QCD February 10, 2012 Taken From: A. Metz, INT Workshop on Orbital Angular Momentum in QCD February 10, 2012 Predict: A y ~α em m q /Q ~10 -4 Photons Coupling to Different Quarks Predict: A y ~ 10 -2

Kinematics 7/1/1322 Beam Polarimetry (Møller + Compton) Luminosity Monitor Measured 3 He(e,e’) SSA using BigBite and Left HRS in singles mode.

HERMES proton data 7/1/1323 A. Airapetian et al, Phys. Lett. B682, 351 (2010) New Results: A y n in DIS Measured average: A y = 0.94 ± 0.32 x NEW A y n

Topic 3: SSA in quasi-elastic 3 He(e,e’n) Detect recoil neutron during QE scattering. Christ-Lee theorem doesn’t apply for semi-inclusive scattering. A y not necessarily zero Sensitive to final state interactions PWIA predicts A y =0 Precise laboratory for studying details of 3 He wavefunction Unpublished NIKHEF result showed A y =50% at Q 2 =0.1 GeV 2 7/1/1324 Semi-Inclusive Target SSA

Preliminary Results 7/1/ Detect recoil neutron using Hall A Neutron Detector (HAND) -- A y changes by 2 orders of magnitude between Q 2 = GeV Agree with theory that includes FSI and MEC -- Beautiful demonstration of transition from nucleus to nucleon degrees of freedom

Summary 7/1/1326 First measurements of the inclusive target SSA using vertically polarized 3 He in QE, DIS scattering. Large QE SSA observed at Q 2 =1 GeV 2 ; Predicted by GPD moment model. -- Remains large down to Q 2 =0.14 GeV 2 DIS SSA appears much larger than predicted by Afanasev et al., consistent with Metz et al. Measurements at high Q 2 possible with Jefferson Lab at 12 GeV. Precision results for SSA in 3 He(e,e’n). Strong Q 2 dependence. Sensitive to few body physics in 3 He Must pay attention to TPEX as precision of experiments improve

7/1/1327 S, S’, D, Δ-isobar contributions to 3 He wavefunction Phys. Rev. C65, (2002) 3 He as a neutron

Check for False Asymmetries: Luminosity Asymmetry 7/1/1328 ppm

Backgrounds BigBite: Pair produced e + /e - pairs from π o decay. –Measure using positive polarity –>50% contamination in lowest momentum bin –1% in largest momentum bin –Largest systematic uncertainty BigBite: π -/+ in e -/+ spectrum. No Cherenkov detector. EM pre-shower and shower calorimeter LHRS spectrometer, virtually background free. –Good PID –Highest momentum = negligible pair-electron contamination 7/1/1329

Contaminations Good Agreement among all trigger types for positron contaminations with pion contamination corrected (central results only) Pion contaminations dominated by systematic uncertainties. Pion contamination are obtained by looking at the preshower energy deposition. Also compared with BigBite GEANT3 MC and checked with HRS Pion rejector for systematic uncertainties 7/1/1330