1. TAPS October 2004  Martin Kotulla, University Basel Magnetic Moment of the S 11 (1535) Resonance

2. Motivation SPS 2004 Martin Kotulla, Universität Basel S 11 (1535) structure:  unusual couplings  (S 11 (1650):  )  quasi bound  molecule? MDM measurement:  internal  transition  interpretation with reaction model MDM predictions:  (qqq):  (S 11 + )=1.89  N  (S 11 0 )=-1.28  N  (  ):  (S 11 + )=1.86  N  (S 11 0 )=-0.56  N  (qqq):  (S 11 + )=1.1  N  (S 11 0 )=-0.25  N  („  “):  (S 11 + )=1.55  N  (S 11 0 )=-0.74  N Chiang et al., NPA 721 (2003) 731 Chiral Unitary M.: Hyodo et al., nucl-th/0305023 N. Kaiser et al., PRB 362, (1995) 23

3. Resonant mechanism SPS 2004 Martin Kotulla, Universität Basel accessible resonaces:   (1232) via:  p     ´  p,    p     ´  p  + : M.K. et al., PRL 89, 272001 (2002)  ++ : various extractions: PDG2002  S 11 (1535) via:  p   ´  p comparison of elastic (non radiative) reaction:

4. Reaction Model I SPS 2004 Martin Kotulla, Universität Basel  p   p : (proton target)  total cross section: 10nb  sensitivity of  energy differential cross section higher differential cross section photon asymmetry  Chiang et al., NPA 721 (2003) 731

5.  beam asymmetry SPS 2004 Martin Kotulla, Universität Basel beam asymmetry:  D 13 (1520) branching ratio to  : 0.08%  S 11 (1535) branching ratio to  : 50%  asymmetry determined by interference of S 11 and D 13 GRAAL data

6. Reaction Model II SPS 2004 Martin Kotulla, Universität Basel  n   n : (deuteron target)  total cross section: ~1 nb (900MeV)  no background radiation from proton bremsstahlung ( ) energy differential cross section very sensitive to MDM  quasi free process on deuteron? Hyodo et al., nucl-th/0305023

7. Quasifree mechanism SPS 2004 Martin Kotulla, Universität Basel J.Weiss et al., EPJ A (2003) 275  n   n : (deuteron target)  participant (neutron!) detection necessary (TAPS)  proposed energy range 850-950 MeV  missing mass of spectator nucleon  quasi-free nature of the reaction ?

8. Quasifree mechanism SPS 2004 Martin Kotulla, Universität Basel  n   n : (deuteron target)  momentum distributions of the spectator nucleon p x, p y, p z centered around zero above 700 MeV  quasi-free nature of the reaction  FSI and bound state effects neglectable J.Weiss et al., EPJ A (2003) 275

9. Summery SPS 2004 Martin Kotulla, Universität Basel motivation:  magnetic moments carry valuable structure information  MDM measurement feasible for  (1232) and S 11 (1535)  pioneering experiment: S 11 (1535) accessible with CB/TAPS  S 11 + via proton target and polarization  ambitious: S 11 0 via deuterium target: dominated by S 11 0  S 11 0  ´ reactions:   p   p : cross section 10nb (at 900MeV)   n   n : cross section 1nb (at 900MeV) improvements:  (double) polarized data „must“ increase the sensitivity