for the A1 collaboration Measurements with polarized 3He at MAMI D. Rohe for the A1 collaboration 3He at low Q2 (< 0.4 GeV/c2) Results for 3He(e,e¢p)d and 3He(e,e¢p)np Setup for Gen measurement at Q2 = 0.25 (GeV/c)2 Corrections and result (preliminary) Summary

3He as polarized neutron target n is bound in 3-body system Extrapolation to free neutron target 3He n theoretical correction needed due to reaction mechanism nuclear structure dependent on the - kinematics - reaction channel Modern 3-body calculation: e.g. non-relativistic Faddeev calculation (Bochum-Krakow group) applicable for Q2 < 0.4 (GeV/c)2 ~ treating full FSI and MEC

Experimental measure of FSI and MEC contributions: Target asymmetry Ayo via 3He (e,e¢ n) 3He spin ^ scattering plane PWIA: Ayo = 0 (invariance under time reversal) + FSI, MEC: Ayo  0 Result: Bochum-Krakow group FSI FSI + MEC Gep = Gmp = 0 (no charge exchange) A_y_3.agr J.Bermuth, P.Merle et al., Phys. Lett. B 564, 199 (2003)

Theoretical corrections to Gen from 3He (e,e¢ n) increasing with decreasing Q2 example: Q2 = 0.67 (GeV/c)2: (3.4 ± 1.7) % due to FSI (C. Carasco, et al., Phys. Lett. B 559, 41 (2003)) Q2 = 0.35 (GeV/c)2: ~ 25% due FSI Q2 = 0.25 (GeV/c)2: large corrections measured at MAMI/A1 Q2 = 0.15 (GeV/c)2: FSI + MEC important to test reliability of theory data help to understand nuclear structure & reaction mechanisms

ST Setup in spectrometer hall at MAMI e¢ e rotation of the target spin spectr. A coils around m - metal 28 msr e¢ B = 4 G o e 53o 29o 735 MeV 68o 3He, 5 bar lead shielding n,p p 1.80 m n,p rotation of the target spin | A+ A- || nucleon detector q A+ || ST A- | spectr. B 5.6 msr, 48.5o

Electron-target asymmetries in q.e. kinematics (Q2=0.31GeV/c2) N( ) - N( ) N( ) + N( ) A = 1 Pe PT Pe = (76.2 +/- 0.2 (stat) +/- 1.3 (syst)) % PT = (49.8 +/- 0.3 (stat) +/- 2 (syst)) % Separation of 2 and 3- body breakup (BB) - reconstruction of the missing energy Em Em = Ee - Ee¢ - Tp¢ - TA-1 3He(e,e’p)d data simulation 3He(e,e’p)pn 2BB 2BB+3BB

FSI: strong influence in 3BB but negligible in 2BB MEC: negligible Results: parallel perpendicular FSI+MEC PWIA Achenbach et al., Eur. Phys. A 25, 177 (2005) very good agreement between data and theory (Golak’s calculation) FSI: strong influence in 3BB but negligible in 2BB MEC: negligible

Interpretation: 2BB: polarized proton target P2BB = (-)1/3 (simple Clebsch-Gordon relation) p n e - d 3He measured : A|| = 12.3 % PWIA (Pp = 100%): A|| = 39.2 % 3BB: in PWIA: both protons are in a S-state P(3BB) = 0 + FSI: mainly rescattering p n e - 3He rescattering direct FSI rescattering small in 2BB and 3BB Singlet +Triplet np T-matrix

Setup in spectrometer hall for Gen at Q2 = 0.25 (GeV/c)2 spectr. A coils around m - metal 28 msr e¢ B = 4 G o e 53o 51.5o 645 MeV 3He p,n lead shielding Kinematics: E Q2 E’e qe qh MeV (GeV/c)2 MeV deg deg 645 0.25 500 53 51.5 nucleon detector

a Gen Gmn sin(qSq) cos(fSq) + b G2mn cos(qSq) Gen measurement via 3He (e ,e´n ) spin orientation plane Kinematics quasielastic ST fSq e´ qSq qe h q 3He n e scattering plane here: ST in scattering plane target - electron asymmetry: N( ) - N( ) N( ) + N( ) A = ST fixed, h flipping a Gen Gmn sin(qSq) cos(fSq) + b G2mn cos(qSq) c G2en + d G2mn = Pe Pn beam neutron polarization

no absolute cross section measurement independent of Pe Pn Ratio of asymmetries: A(qSq =90o) A a Gen ^ = = A(qSq =0o) A b Gmn fSq=0o Advantage: no absolute cross section measurement independent of Pe Pn (we measured it: dPe < 2%, dPT < 4% (rel.)) only relative measurement needed note: PT > Pn possible dilution of the asymmetry drops out - due to unpolarized background - due to charge exchange: Pb(p,n) Further: alternate measurement of , ,- ,- A ^ reduction of systematic errors

Correction to A due to FSI & MEC ^ calculation from J. Golak Cut to avoid large correction (particular MEC) Correction to A : x 1.65 to A : x 1.06 ^ ||

data_gen_corr5_sh preliminary

Summary: 3He as polarized neutron target - at low Q2 large corrections from MEC,FSI - confirmed by Ay measurement test of 3-body theories Separation of 2BB and 3BB on top of the q.e. peak Measurement of A and A in 3He(e,e’p) - 2BB: “polarized proton target”, close to PWIA - 3BB: large FSI effect ^ || very good agreement with theory Measurement of Gen at Q2 = 0.25 (GeV/c)2 preliminary result: statistical error: ~12 % correction factor: 1.6

Understanding of reaction mechanisms & nuclear ground state Modern 3-body calculations: e.g. non-relativistic Faddeev calculation (Bochum-Krakow group) applicable for Q2 < 0.4 (GeV/c)2 ~ Reaction mechanisms - interaction during scattering process: MEC (Meson Exchange Current) p,r p,r - interaction after scattering process: FSI (Final State Interaction) rescattering direct

- correcting the experimental asymmetries Aexp for radiation tail of 2BB in 3BB region A3BB = A2+3BB - A2BB a23 a23 : amount of 2BB in 3BB region (43%) 1 - a23 electron polarization Pe = (76.2 +/- 0.2 (stat) +/- 1.3 (syst)) % target polarization PT = (49.8 +/- 0.3 (stat) +/- 2 (syst)) % Aexp Pe PT A =

N( ) - N( ) ST Principle of the measurement electron-target asymmetry target spin ST fixed in scattering plane, electron helicity h flips parallel asymmetry A||: ST || q perpendicular asymmetry A : ST ^ q ^ rotation of the target spin every hour | A+ A- || e- q A+ || ST A- | magnetic field box