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Crystal Ball Experiment at MAMI: Recent Results and Technical Capabilities for Mesons 2010 Overview

This article provides an overview of the Crystal Ball experiment at MAMI, including its technical capabilities for pion and strangeness production, as well as selected physics topics such as coherent pion and eta photoproduction. It also discusses the exciting future prospects and conclusions of the experiment.

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Crystal Ball Experiment at MAMI: Recent Results and Technical Capabilities for Mesons 2010 Overview

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

  2. Overview • 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

  3. MAMI

  4. MAMI • 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: Eγ = Ee – Ee' • 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 Pe-→Pγcirc.

  6. CB@MAMI Detector System PID Detector MWPCs Target TAPS Crystal Ball • Large solid angle detection: CB & TAPS ~97% 4π • Angular discrimination: 672 NaI, 386 / 512 BaF2 • Particle discrimination: PID, VETOS • Charged tracking: MWPC

  7. Technical Capabilities: Incoherent π0 photoproduction on 12C Decay γ spectrum in coinc. with π0 4.4 MeV 2+ state γ12C→12 C* π0 ↓ 12C γ(4.4 MeV) • First report of σ(γ,π0) for a specific excited state • Simultaneous detection of π0 and 4.4 MeV decay γ in CB • Important first step in isolation of coherent process • PRL 100, 132301 (2008)

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

  9. Coherent π0 photoproduction on 208Pb Preliminary Preliminary Preliminary Preliminary Eγ = 160 - 170 MeV Eγ = 170 - 180 MeV Eγ = 180 - 190 MeV Eγ = 190 - 200 MeV Preliminary Preliminary Preliminary Preliminary • 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

  10. Excitations of the Nucleon Δ(1232) 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

  11. TAPS at MAMI CB at ELSA CB@MAMI preliminary η photoproduction: γp→ηp TAPS/MAMI GRAAL/ESRF CLAS/JLAB CB/ELSA • S11(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

  12. η photoproduction: γp→ηp S11(1535) JLAB ELSA CB@MAMI preliminary (S. Prakhov) JP = 1/2 - JP = 3/2 - D13(1520) • S11(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

  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 Data G4 total G4 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

  15. Recoil Polarimetry – π0 Photoproduction Degree of Polarisation Transfer Cx' 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 • 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...

  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. 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

  18. Polarised Frozen Spin Target N. Froemmgen P=P0exp(t/τ) • Frozen spin target fully functioning – Polarization > 90% • ~1000 hours relaxation time & low He usage – long measurement time! • Running with transverse polarized target!

  19. First measurement of transverse spin observable F in γp→π0p N. Froemmgen • F asymmetry: circ. polarised photons, transverse pol. Target • Need to seperate out contribution from 12C and 16O and 3/4He • 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!

  20. First measurement of transverse spin observable F in γp→π0p Background Subtraction on MM(π0) Eγ = 300 – 400 MeV Eγ = 400 – 500 MeV cos(φπ-90) = sin (φπ) Eγ = 400 – 500 MeV 0 Eγ = 500 – 600 MeV • Asymmetry calculated for each bin (above) • Normalized to sin(φ) (target polarization angle corr.) • Weighted average for points with |sin(φ)|>0.3 Eγ = 500 – 600 MeV

  21. First measurement of transverse spin observable F in γp→π0p SAID MAID F PRELIMINARY PRELIMINARY 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!

  22. Conclusions & Outlook SAID MAID PRELIMINARY PRELIMINARY PRELIMINARY F F 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: P33(1232), P11(1440), S11(1535) • Double meson production (ππ, πη)→ other resonance studies e.g. D33(1700) • Compton scattering: access to nucleon vector polarisabilities • Strangeness photoproduction, coherent π0 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:P33(1232), P11(1440), S11(1535), • Double meson production ( π→ broad range of new resonance studies P33(1232), S11(1535), D33(1700)!

  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!

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