SFB 443 Crystal Ball Experiment at MAMI Recent

SFB 443 Crystal Ball Experiment at MAMI Recent Results W. J. Briscoe for the A 2 Collaboration (thanks for the sabbatical support) MESONS 2010

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

MAMI

MAMI Maximum Energy 1604 Me. V, ΔE = 100 Ke. V 100 % duty cycle Current ≤ 100 μA Electron Polarization ~ 85% ~7000 hours beam / year

Photon Tagging Facility Detection of radiating electrons: Eγ = Ee – Ee' Energy resolution 2 -4 Me. V Tagger Microscope ~6 x 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 Pe-→Pγcirc. Point Tagger awaiting funding

CB@MAMI Detector System TAPS Crystal Ball PID Detector MWPCs Target

Technical Capabilities: Incoherent π0 photoproduction on 12 C Decay γ spectrum in coinc. with π0 4. 4 Me. V 2+ state γ 12 C→ 12 C* π0 ↓ 12 C γ(4. 4 Me. V) First report of σ(γ, π0) for a specific excited state Simultaneous detection of π0 and 4. 4 Me. V decay γ in CB Important first step in isolation of coherent process PRL 100, 132301 (2008)

Technical Capabilities: Kaon Photoproduction Incident and decay subcluster time difference Decay sub-cluster energy Decay sub-cluster from K+→μ+νμ decay ~ 20 ns Incident subcluster from K+ ~3 ns K+ missing mass Tom Jude Edinburgh University

in ar y el Pr y ar ar im el Pr in in ar im el Pr Eγ = 190 - 200 Me. V y Eγ = 180 - 190 Me. V in ar in im el Pr im in ar y im el Pr Eγ = 170 - 180 Me. V y Eγ = 160 - 170 Me. V y Pr Pr el el im im in ar y Coherent π0 photoproduction on 208 Pb 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

Excitations of the Nucleon Δ(1232) 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

η photoproduction: γp→ηp TAPS/MAMI GRAAL/ESRF CLAS/JLAB CB/ELSA 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

η photoproduction: γp→ηp JLAB ELSA CB@MAMI preliminary (S. Prakhov) S 11(1535) JP = 1/2 - JP = 3/2 D 13(1520) 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

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!

Recoil Polarimetry Data G 4 total G 4 no nuclear int Proton scattering angle in graphite π0 / η decays & is detected as normal Reconstruct π0 / η Recoiling proton then tagged Preconstructed = γbeam + ptarget – π0 Large scattering angle → nucl. interaction Asymmetry gives pol. transfer D. P. Watts , Edinburgh D. Glazier, Edinburgh M. Sikora, Edinburgh. D, Howdle, Glasgow

Degree of Polarisation Transfer Cx' Recoil Polarimetry – π0 Photoproduction Photon Energy p(γ, π0)p polarisation transfer: circ. polarised beam to recoil proton D. P. Watts, Edinburgh D. Glazier, Edinburgh M. Sikora, Edinburgh D, Howdle, Glasgow

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

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

First measurement of transverse spin observable F in γp→π0 p N. Froemmgen 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!

First measurement of transverse spin observable F 0 in γp→π p 0 Background Subtraction on MM(π ) cos(φπ-90) = sin (φπ) Eγ = 300 – 400 Me. V Eγ = 400 – 500 Me. V 0 Eγ = 500 – 600 Me. V Asymmetry calculated for each bin (above) Normalized to sin(φ) (target polarization angle corr. ) Weighted average for points with |sin(φ)|>0. 3

First measurement of transverse spin observable F in γp→π0 p F SAID MAID PRELIMINARY V. Kashevarov World first measurement of F – VERY PRELIMINARY! Need more work on Pγ (currently standard conditions assumed) Need to extend to full solid angle coverage (measure with TAPS) Ptarg from average over time – need event-by-event normalisation However – everything works!

F Conclusions & Outlook F SAID MAID PRELIMINARY V. Kashevarov 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 π0 studies of isotope chains η/η' decays & more. . .

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

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

Polarized Target

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

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!