Helicity dependence of g n ® Nπ(π) and the GDH integral on the neutrom Update of the Proposal A2-9/2005 Spokepersons: P. Pedroni INFN-Sezione di Pavia, Italy J. Annand University of Glasgow, UK W.J. Briscoe GWU, Washington, USA J.Krimmer IP, University of Mainz, Germany O.Jahn IKP, University of Mainz, Germany

Goals of the experiment First measurement of the total helicity dependent cross section on 3He [200-1400 MeV] (Substantial) statistical improvement of the existing total helicity dependent deuteron data in the photon energy range [800-1400 MeV] First measurement of the helicity dependent g n ® Np(p) channels (mainly using deuterons) [200-1400 MeV] NEW

Experimental verification of the GDH sum rule Proposed in 1966 Prediction on the absorption of circularly polarized photons by longitudinally polarized hadrons photon-spin hadron-spin photon-spin hadron-spin sa sp Anomalous magnetic moment

Why could the GDH sum rule be violated ? The only “weak” hypothesis is the assumption that Compton scattering gN ® g’ N’ becomes spin independent when n ® ¥ A violation of this assumption can not be easily explained Possible hypotheses for violation: Exchange of a1-like (J=1+) mesons between g and N Non pointlike (constituent) quarks ? Photoproduction of gravitons ?

GDH sum rule predictions 3He m 2.79 -1.91 0.86 -2.13 k 1.79 -1.92 -0.14 -8.37 IGDH 204 233 0.65 498 (n.m.) (mb) “naive” expectations

AFS model Arenhoevel, Fix, Schwamb, PRL 93, 202301 (04) pNN pN from MAID +nuclear effects ppNN EPJA 25,114 (05) p0d PLB 407,1 (97) pn NPA 690,682 (01)

Model from Golak-Gloeckle

GDH sum rule on the proton Eg (GeV) IGDH (mb) 0.14-0.20 * MAID03 SAID04 -29 -28 0.20-2.90 Measured (Mainz+Bonn) 254±5±12 > 2.90 (Regge approach) Simula et al. Bianchi-Thomas -13 -14 Total 211±5±12 GDH sum rule 205 * Low energy theorems in the Np threshold region (multipole analyses not very wrong ...)

GDH sum rule: predictions (2009) Proton IGDH (mb) Neutron IGDH (mb) g p ® Np 172 [164] g p ® Npp 94 g p ® Nh -8 g p ® KL (S) -4 g p ® Nr(w) 0 Regge contrib. -14 (Eg > 2 Gev) g n ® Np 147 [131] g n ® Npp 82 g n ® Nh -6 g n ® K L(S) 2 g n ® Nr(w) 2 Regge contrib. 20 TOTAL 239 [231] 244 [231] GDH 205 233 Np : SAID-FA07K [MAID07] KL(S) : Sumowidagdo et al., PRC 65,0321002 (02) Npp : Fix, Arenhoevel EPJA 25, 114 (2005) Nh : MAID Nr : Zhao et al., PRC 65, 032201 (03) Regge : Bianchi-Thomas , PLB 450,439(99)

GDH data Sensitivity to E2-*M2- PRL 88, 232002, 2002 SAID (SM01) to reproduce the data: MAID2000 Sensitivity to E2-*M2-

GDH sum rule on the neutron No Free neutron target available Model dependent results from nuclear targets Experimental goal: to have a “small” and “realiable” model dependence Two different (and complementary) targets =) deuterated butanol =) high pressure 3He target Measurement of partial channels like

GDH sum rule on the neutron p n 2H: m ~ mp + mn Þ ­ ­ IGDHneutr. ~ IGDHdeut.-IGDHprot. -INuclear 3He: m ~ mn Þ ­ ­ ¯ (S-state with ~ 90% prob.) IGDHneutr. ~ IGDHHe3-a·IGDHprot. -INuclear (a ~ 10%) 3He better suited to get IGDHneutr (inclusive method) 2H better suited to measure partial channels

Status on the deuteron results

Results on the deuteron Statistical precision to be improved AFS MAID

Status on the 3He results

Measurements of different observables on many partial channels Partial channel measurement e.m. interaction does not conserve isospin 3 different reaction amplitudes A0 A1/2 A3/2 measurements on both the proton and the neutron are needed Different N* decay modes: Determination of the baryon resonance properties Measurements of different observables on many partial channels

Complete characterization of the different isospin components Different resonance excitations

Helicity dependent cross sections

Unpolarized cross sections

° GDH g p -> n p+ Preliminary · GDH coll Preliminary Fix -Arenhoevel Levchuk et al. ° GDH g p -> n p+ EPJA 26, 135 (05) Preliminary

Experimental set-up CB+TAPS+PID+MWPC Longitudinally polarized Deuterated Butanol Longitudinally polarized 3He gas target (6 bars) (presentation by J.Krimmer) Moeller Polarimeter Cerenkov detector (online suppression of e.m. background / very open CB-TAPS trigger)

Total inclusive cross section (not feasible) (inclusive method) For each partial reaction channel, at least one reaction product has to be detected with (almost) complete acceptance (solid angle & efficiency) detector with a very high acceptance/particle detection efficiency (CB+TAPS: 97% of 4p) Suppression of e.m. events (pair prod./Compton) at forward angles

Beam time estimate Deuteron: 950 hours related to unpolarized target nucleons 3 different electron beam energies: 525, 850, 1500 MeV Deuteron: 950 hours 3He (6 bars) : 960 hours (preliminary evaluation) now Total inclusive: Single pion: