1. Recent Results from the CB@MAMI Programme at the Glasgow Tagged Photon Spectrometer in Mainz E. J. Downie University of Glasgow

2. Introduction Introduction to the CB@MAMI experimental series Physics highlights of first round Experiment to measure the MDM of (1232) Glasgow Photon Tagger upgrade / MAMI-C Anticipated physics of round II

3. The Need for CB@MAMI Experiments Detailed information on nucleon & resonances test QCD N resonances: short lifetime difficult to measure properties Large Breit Wigner widths can't accurately determine spect. Need more experimental information

4. Unique capabilities of CB@MAMI Well understood probe: photon Ability to accurately separate final states: good det. resolution Sensitivity to small processes: 4 detection, large flux Access to polarisation observables: pol. beam, target, recoil

5. The CB@MAMI Set-up – Electron Beam MAMI B Up to 883 MeV e - beam 100 % duty factor Current up to 100 A Polarised e - Very stable beam MAMI-A 180 MeV MAMI-B 883 MeV

6. The CB@MAMI Set-up – Photon Beam Glasgow Photon Tagging Spectrometer Pass e - beam through radiator Magnetic spectrometer for e - Tags bremsstrahlung Photon beam enters expt. Timing coincidence Polarised e - 80% circ. pol. Crystalline rad. lin. pol.

7. The CB@MAMI Detector Set-up High rate 2MeV resolution tagged photon beam Liquid H 2 /D 2, 208 Pb, 40 Ca, 16 O, 12 C and other nuclear targets Two EM calorimeters 4 spectrometer set-up MWPC & PID for tracking and ID of charged particles Ideal for high precision / low cross section measurements Glasgow Photon Tagging Spectrometer

8. The CB@MAMI Detector Set-up High rate 2MeV resolution tagged photon beam Liquid H 2 /D 2, 208 Pb, 40 Ca, 16 O, 12 C and other nuclear targets Two EM calorimeters 4 spectrometer set-up MWPC & PID for tracking and ID of charged particles Ideal for high precision / low cross section measurements

9. The CB@MAMI Detector Set-up – The PID Pions Protons Built by Glasgow & Edinburgh E (PID) / E (CB) 2mm scint. barrel Identified p / +/- / e - / d PID II by Edinburgh & Glasgow

10. The Magnetic Dipole Moment of the + (1232) Nucleon structure very difficult to probe Predictions of very sensitive to the baryon model used EM properties of nucleon excited states largely unmeasured Spin precession in a magnetic field wholly unsuitable Experimental test of theoretical models

11. The Magnetic Dipole Moment of the + (1232) Tagged photon beam on liquid H2 + lifetime 10 -24 s large Breit-Wigner width Created + at upper end of B-W width + radiatively decays to another + + + P 0 p(uud) + (uud)

12. The Magnetic Dipole Moment of the + (1232) Comprehensive measurement required: Measure two channels: p(, ' 0 p), p(, ' + n) Measure several observables: Five-fold differential cross section Linearly polarised photon asymmetry Circularly polarised photon asymmetry p(, ' 0 p) Experimentally difficult channel: ~50nb cross section Backgrounds: p(, 0 p), 318 b; p(, 0 0 p), 1.5 b

13. The Magnetic Dipole Moment of the + (1232) M(initial + ) M(final + ) M(sum) E miss. data E miss. sim. M 2 miss. ( 0 p) data M 2 miss. ( 0 p) sim.

14. The Magnetic Dipole Moment of the + (1232) Total cross section of p(, ' 0 p) Expect improvement in statistical error: kinematic fitting background subtraction improvement This Work - preliminary Kotulla et al. P.R.L. 89 (2002)

15. The Magnetic Dipole Moment of the + (1232) Differential of p(, ' 0 p) Improvement in acceptance calculation expected Fully diff. being calculated by Mainz / Basel students S. Schuman, Mainz Kotulla et al. P.R.L. 89 (2002)

16. The Magnetic Dipole Moment of the + (1232) Linearly polarised photon asymmetry of p(, ' 0 p) Variation with E( ') important model constraint First ever measurement!

17. The Magnetic Dipole Moment of the + (1232) Chiang et al. P.R.C. 71 (2005) Pascalutsa & Vanderhaeghen P.R.L. 94 (2005)

18. The Magnetic Dipole Moment of the + (1232) p(, ' + n) results PID & shower shape Good + energy determination Can measure n + decay of + with CB !! Proof of principle established more detailed meas. planned D. Glazier & D. Watts, Edinburgh ') MeV (linearly Polarised) ') GeV (circ. Polarised)

19. Other CB@MAMI Round I Physics Highlights mass determination Find prod. threshold A. Nikolaev, Bonn Without Acceptance Correction

20. mass determination p(, 0 0 p) production Test of PT Circ. asymmetry Reaction mechanism? N resonance properties? A. Nikolaev, Bonn Without Acceptance Correction Bernard et al. Phys. Lett. B382 (1996) Kotulla et al. Phys. Lett. B578 (2004) F. Zehr, Basel Double 0 Excitation Function Other CB@MAMI Round I Physics Highlights D. Krambrich, Mainz

21. mass determination p(, 0 0 p) production p(, 0 p) photon asymmetry Massive statistics High resolution EM properties of E2/M1 ratio E. Downie R. Leukel, Mainz, 2001 E. Downie, Glasgow VERY PRELIMINARY >0.5 of data set Other CB@MAMI Round I Physics Highlights

22. Coherent 0 production Do heavy stable nuclei have a neutron skin? Fundamental property of nuclear physics Size of skin gives direct information on neutron rich equation of state Skin size also gives important new insights into neutron star physics (cooling mechanisms, mass radii relationships) Accuracy < 0.05 fm C. Tarbert, D. Watts, Edinburgh See D. Watts talk CB@MAMI Highlights I

23. 16 O 6.1 MeV 12 C 4.4 MeV See low E nuclear decay 's In coincidence ! 550 MeV invariant mass 135 MeV 0 invariant mass 4.4 MeV Carbon decay photon New possibilities for range of nuclear physics studies e.g. transition matter form factors 0 C. Tarbert, Edinburgh CB@MAMI Highlights I

24. MAMI-C / Photon Tagger Upgrade MAMI-A MAMI-B MAMI-A 180 MeV MAMI-B 883 MeV

25. MAMI-C / Photon Tagger Upgrade MAMI – C Now Operational! MAMI-A MAMI-B MAMI-A 180 MeV MAMI-B 883 MeV MAMI–C 1.5 GeV

26. MAMI-C / Photon Tagger Upgrade Tagger Tagger has to bend 1.5 GeV Need to increase B to 1.8T Complete Tagger dismount Reduce pole gap Increase return yoke Tagger reassembled 2T field achieved Sucessfully running @ 1.5GeV!

27. MAMI-C / Photon Tagger Upgrade

28. 1.5 GeV Beam Spot See Eillidh McNicoll's talk

29. High flux allows possibility of recoiling nucleon polarimetry Graphite scatterer + PID/Tracking detectors Scatter > 10 : Hadronic interaction n(, ) =n o ( ){1+A( )[P y cos( )–P x sin( )]} First complete measurement of meson (p,n..) production Enable first fully constrained PWAs CB@MAMI Future Facilities: Edinburgh Recoil Polarimeter n() =n o (){1+A()[P y cos()– P x sin()]}

30. Recoil polarisation expts. Frozen spin target – double pol. experiments S 11 (1535) Magnetic Moment Threshold strangeness production Short range correlations Tests of fundamental symmetries, ' decays Medium modification of mesons ( ral sym. restoration) Sum rules – GDH... Vector meson production -mesic nuclei VERY PRELIMINARY >0.5 of data set CB@MAMI 1.5GeV Expected Future Highlights

31. Initial round of CB@MAMI experiments complete Results are approaching publication MAMI C running at 1.5GeV Tagger upgrade sucessfully complete Broad range of nuclear and hadronic physics planned Watch this space for interesting physics! Conclusions

32. The CB@MAMI Detector Setup – The PID Designed and build by Edinburgh / Glasgow Universities