1. Crystal Ball Experiment at MAMI Recent Results W.J. Briscoe for the A2 Collaboration (thanks for the sabbatical support) MESONS 2010 SFB443

2.  Overview of MAMI and the Crystal Ball experimental setup  Technical capabilities: pion production, strangeness production from the proton and neutron  Selected physics topics:  Coherent pion photoproduction  Eta photoproduction  Complete measurements: Transverse spin observables in pion and eta photoproduction  Conclusions & Outlook Overview

3. MAMI

4.  Maximum Energy 1604 MeV, ΔE = 100 KeV  100 % duty cycle  Current ≤ 100 μA  Electron Polarization ~ 85%  ~7000 hours beam / year

5. Photon Tagging Facility  Detection of radiating electrons: E γ = E e – E e '  Energy resolution 2-4 MeV  Tagger Microscope ~6x better E res.  Circularly pol. γ from e - pol, upto 85%  Linearly pol. γ from crystalline rad., upto 70%  Collimation upgrade will give +5% pol.  End Point Tagger awaiting funding P e- →P γcirc.

6. CB@MAMI Detector System  Large solid angle detection: CB & TAPS ~97% 4π  Angular discrimination: 672 NaI, 386 / 512 BaF 2  Particle discrimination: PID, VETOS  Charged tracking: MWPC Crystal Ball TAPS PID Detector MWPCs Target

7.  First report of σ(γ,π 0 ) for a specific excited state  Simultaneous detection of π 0 and 4.4 MeV decay γ in CB  Important first step in isolation of coherent process  PRL 100, 132301 (2008) Technical Capabilities: Incoherent π 0 photoproduction on 12 C Decay γ spectrum in coinc. with π 0 4.4 MeV 2+ state γ 12 C→ 12 C* π 0 ↓ 12 C γ(4.4 MeV)

8. Technical Capabilities: Kaon Photoproduction  No time left to discuss: Recoil polarimetry: γN→πN', γN→ηN', determination of η mass, GDH integral on the neutron, in-medium modification of mesons, threshold hyperon production, double pion production and so much more... Decay sub-cluster energy Incident and decay sub- cluster time difference K + missing mass Incident subcluster from K + ~3ns Decay sub-cluster from K + →μ + ν μ decay ~ 20ns Tom Jude Edinburgh University

9. Coherent π 0 photoproduction on 208 Pb Eγ = 160 - 170 MeVEγ = 190 - 200 MeVEγ = 170 - 180 MeVEγ = 180 - 190 MeV  Do heavy stable nuclei have a neutron skin?  Size of skin gives direct information on equation of state of n-rich matter  Skin size gives important new insights into neutron star physics!  Measurements planned on Sn, Ca isotope chains  Accuracy ~0.05 fm D. P. Watts and C. Tarbert, Edinburgh Preliminary

10.  Many resonances: broad and overlapping  Accurate separation of final states → good detector resolution  Sensitivity to small σ processes → 4π detector acceptance, large γ flux  Access to polarization observables → polarized beam, target, recoil Excitations of the Nucleon Δ(1232)

11. η photoproduction: γp→ηp  S 11 (1535) dominant resonance in η production  “Dip” in cross section due to interference with less dominant resonances  Need polarization observables to extract full resonance composition TAPS at MAMI CB at ELSA CB@MAMI preliminary TAPS/MAMI GRAAL/ESRF CLAS/JLAB CB/ELSA

12.  S 11 (1535) dominant resonance in η production  “Dip” in cross section due to interference with less dominant resonances  Need polarization observables to extract full resonance composition JLAB ELSA CB@MAMI preliminary (S. Prakhov) S 11 (1535) J P = 1/2 - J P = 3/2 - D 13 (1520) η photoproduction: γp→ηp

13. Complete Experiment  16 possible unpolarised, single & double polarization observables in pseudoscalar meson photoproduction  Need 8 carefully selected observables to fully constrain partial wave analyses  These have to include single & double polarization observables  All polarization degrees of freedom now uniquely accessible in Mainz!

14. Recoil Polarimetry  π 0 / η decays & is detected as normal  Reconstruct π 0 / η  Recoiling proton then tagged  P reconstructed = γ beam + p target – π 0  Large scattering angle → nucl. interaction  Asymmetry gives pol. transfer Data G4 total G4 no nuclear int Proton scattering angle in graphite D. P. Watts, Edinburgh D. Glazier, Edinburgh M. Sikora, Edinburgh. D, Howdle, Glasgow

15. Recoil Polarimetry – π 0 Photoproduction  No time left to discuss: Recoil polarimetry: γN→πN', γN→ηN', determination of η mass, GDH integral on the neutron, in-medium modification of mesons, threshold hyperon production, double pion production and so much more... Photon Energy Degree of Polarisation Transfer C x '  p(γ,π 0 )p polarisation transfer: circ. polarised beam to recoil proton D. P. Watts, Edinburgh D. Glazier, Edinburgh M. Sikora, Edinburgh D, Howdle, Glasgow

16. Polarized Frozen Spin Target H. Ortega Spina  Uses DNP to achieve ~ 90 % proton, 80 % deuteron  Needs: Horiz. Dilution cryostat, polarizing magnet, microwave, NMR  Two holding coils: solenoid → longitudinal, saddle coil → transverse

17.  Uses DNP to achieve ~ 90 % proton, 80 % deuteron  Needs: Horiz. Dilution cryostat, polarizing magnet, microwave, NMR  Two holding coils: solenoid → longitudinal, saddle coil → transverse Polarised Frozen Spin Target

18.  Frozen spin target fully functioning – Polarization > 90%  ~1000 hours relaxation time & low He usage – long measurement time!  Running with transverse polarized target! N. Froemmgen P=P 0 exp(t/τ)

19. First measurement of transverse spin observable F in γp→π 0 p  F asymmetry: circ. polarised photons, transverse pol. Target  Need to seperate out contribution from 12 C and 16 O and 3/4 He  Requiring proton removes coherent contributions  Other kinematic cuts and remaining underground fitted & subtracted  Data shown from 39 hours minus, 39 hours plus pol. test data, no TAPS  Test beamtime ended 07:00 08.03.10, results first shown 10:00 10.03.10  VERY PRELIMINARY! N. Froemmgen

20.  Asymmetry calculated for each bin (above)  Normalized to sin(φ) (target polarization angle corr.)  Weighted average for points with |sin(φ)|>0.3 Background Subtraction on MM(π 0 ) E γ = 500 – 600 MeV E γ = 400 – 500 MeV E γ = 400 – 500 MeV E γ = 500 – 600 MeV E γ = 300 – 400 MeV cos(φ π -90) = sin (φ π ) 0 First measurement of transverse spin observable F in γp→π 0 p

21.  World first measurement of F – VERY PRELIMINARY!  Need more work on P γ (currently standard conditions assumed)  Need to extend to full solid angle coverage (measure with TAPS)  P targ from average over time – need event-by-event normalisation  However – everything works! PRELIMINARY F First measurement of transverse spin observable F in γp→π 0 p SAID MAID V. Kashevarov

22. Conclusions & Outlook F PRELIMINARY SAID MAID F  The CB@MAMI experimental setup is a highly flexible 4π detector system  Complete measurements of π and η production within next five years  Allow full investigation of: P 33 (1232), P 11 (1440), S 11 (1535)  Double meson production (ππ, πη) → other resonance studies e.g. D 33 (1700)  Compton scattering: access to nucleon vector polarisabilities  Strangeness photoproduction, coherent π 0 studies of isotope chains  η/η' decays & more...  The CB@MAMI experimental setup is a highly flexible 4π detector system  Complete measurements of π and η production within next five years  Allow full investigation of:P 33 (1232), P 11 (1440), S 11 (1535),  Double meson production ( π → broad range of new resonance studies P 33 (1232), S 11 (1535), D 33 (1700)! V. Kashevarov

23. Polarized Target 2 cm  Uses DNP to achieve ~ 90 % proton, 80 % deuteron  Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR  Two holding coils: solenoid → longitudinal, saddle coil → transverse  Detectors have to move

24. Polarized Target  Uses DNP to achieve ~ 90 % proton, 80 % deuteron  Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR  Two holding coils: solenoid → longitudinal, saddle coil → transverse  Detectors have to move

25. Polarized Target

26. Polarised Target  Uses DNP to achieve ~ 90 % proton, 80 % deuteron  Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR  Two holding coils: solenoid → longitudinal, saddle coil → transverse  Detectors have to move

27. Conclusions We are running a full program of Transverse proton and neutron (deuteron) polarized target measurements. (Longitudinal will follow.) Circularly and linearly polarized tagged photons. Have preliminary results for F. MAMI B and MAMI C experiments are being analyzed and prepared for publication by a large group of students. Expect at least a 5 year program with CB and TAPS at MAMI!