1 / 30

Michael Dugger* Arizona State University

S = 0 pseudoscalar meson photoproduction from the proton:. γ p → π 0 p, γ p → π + n γ p → η p, γ p → η ' p. Michael Dugger* Arizona State University. *Work at ASU is supported by the U.S. National Science Foundation. 1. Outline. Motivations – Theoretical & Practical

gage
Download Presentation

Michael Dugger* Arizona State University

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. S = 0 pseudoscalar meson photoproduction from the proton: γ p → π0 p, γ p →π+ nγ p →η p, γ p →η' p Michael Dugger* Arizona State University *Work at ASU is supported by the U.S. National Science Foundation 1

  2. Outline • Motivations – Theoretical & Practical • Experimental Facilities • New and Existing Data • Brief Look At Models • Conclusions/What’s Next *Work at ASU is supported by the U.S. National Science Foundation 2

  3. Motivations • Theoretical • Practical *Work at ASU is supported by the U.S. National Science Foundation 3

  4. Motivations (Theoretical) • Pions are the lightest mesons and are copiously produced in the strong interaction. • The η and η' mesons have isospin ½ and limit one step excited states of the proton to also be isospin ½. The η and η‘ act as isospin filters to the resonance spectrum. This might be useful for find “missing” resonances • The η and η' have strange content but no net strangeness: May be useful in determining differing strange quark content of the proton • The η' is the only isosinglet. This can be used to indirectly probe gluonic coupling to the proton *Work at ASU is supported by the U.S. National Science Foundation 4

  5. Motivations (Practical) Photoproduction: • Electromagnetic interactions are well understood • Real photons are particularly simple: Only 2 polarization states. Non-strangeness reactions: • The outgoing proton is easy to identify and has relatively little contamination *Work at ASU is supported by the U.S. National Science Foundation 5

  6. Experimental Facilities: • SAPHIR (Spectrometer Arrangement for Photon induced Reactions. ELSA) • CLAS (CEBAF Large Acceptance Spectrometer. JLab) • CB-ELSA (Crystal Barrel at ELSA) • GRAAL (at the ESRF in Grenoble) *Work at ASU is supported by the U.S. National Science Foundation 6

  7. SAPHIR at Bonn Electron Stretcher • Photon energies up to 3.0 GeV • Good for charged particles • Small acceptance Drift chamber Electrocalorimeter Time of flight Magnet *Work at ASU is supported by the U.S. National Science Foundation 7

  8. CLAS • Photon energies up to 5.7 GeV • Good for charged particles • Large acceptance *Work at ASU is supported by the U.S. National Science Foundation 8

  9. CB-ELSA • Photon energies up to 3.2 GeV • Good for neutral particles • Large acceptance TAPS Crystal Barrel *Work at ASU is supported by the U.S. National Science Foundation 9

  10. GRAAL • Photon energies up to 1.1 GeV • Good for neutral particles • Large acceptance Variable collimator Fixed collimator Plastic scintillator barrel Cleaning magnet Target Cylindrical wire chambers BGO calorimeter Vacuum system Shielding wall Scintillator and lead sandwich *Work at ASU is supported by the U.S. National Science Foundation 10

  11. New γ p → π0 p Results • New results from GRAAL: dσ/dΩ and Σ • New results from CLAS: dσ/dΩ *Work at ASU is supported by the U.S. National Science Foundation 11

  12. New GRAAL γ p →π0 p Results • SAID • BONN-PNPI • (Anisivich, Klempt) • dσ/dΩfrom 555 to 1021 MeV • MAID *Work at ASU is supported by the U.S. National Science Foundation 12

  13. New GRAAL γ p →π0 p Results • SAID • BONN-PNPI • (Anisivich, Klempt) • dσ/dΩfrom 1036 to 1496 MeV • MAID *Work at ASU is supported by the U.S. National Science Foundation 13

  14. New GRAAL γ p →π0 p Results • SAID • BONN-PNPI • (Anisivich, Klempt) • Σfrom 1036 to 1496 MeV • MAID *Work at ASU is supported by the U.S. National Science Foundation 14

  15. Preliminary CLAS γ p →π0 p Results • dσ/dΩfrom 0.675 to 1.425 GeV • SAID (Blue line) • Mainz (Blue points) • CB-ELSA (Red points) • CLAS (Black points) *Work at ASU is supported by the U.S. National Science Foundation 15

  16. Preliminary CLAS γ p →π0 p Results • dσ/dΩfrom 1.475 to 2.125 GeV • SAID (Blue lines) • CLAS (Blackpoints) • CB-ELSA (Red points) *Work at ASU is supported by the U.S. National Science Foundation 16

  17. γ p →π0 p Polarization Observables Beam polarization Target asymmetry Recoil polarization Double polarization *Work at ASU is supported by the U.S. National Science Foundation 17

  18. Status: γ p →π0 p Database • World data set becoming quite thorough Cross Section • New beam asymmetry and dσ/dΩ measurements from GRAAL • New dσ/dΩ from CLAS • CLAS experiment (g8b) just finished with data taking for beam asymmetry • CLAS double polarization (target & beam) slated for 2007 *Work at ASU is supported by the U.S. National Science Foundation 18

  19. New γ p → π+ n Results • New results from CLAS: dσ/dΩ *Work at ASU is supported by the U.S. National Science Foundation 19

  20. Preliminary CLAS γ p →π+ n Results • Differential cross sections • Eγ from 0.625 to 1.625 GeV • SAID (Blue lines) • CLAS (Black points) *Work at ASU is supported by the U.S. National Science Foundation 20

  21. Preliminary CLAS γ p →π+ n Results • Differential Cross sections • Eγ from 1.675 to 2.275 GeV • SAID (Blue lines) • CLAS (Black points) *Work at ASU is supported by the U.S. National Science Foundation 21

  22. γ p →π+ n Polarization Observables Beam polarization Recoil polarization Target asymmetry Target asymmetry Double polarization *Work at ASU is supported by the U.S. National Science Foundation 22

  23. γ p →π+ n • World database has good coverage for beam polarization, recoil polarization, and target asymmetry between 20° and 120° and up to Eγ = 2300 MeV Cross Section • Double polarization data for G and H between 40° and 100° and up to Eγ = 1900 MeV • New CLAS data to cover dσ/dΩ up to Eγ = 2275 MeV Cross section *Work at ASU is supported by the U.S. National Science Foundation 23

  24. γ p →η p • Data becoming quite thorough • More polarization measurements coming • More dσ/dΩ measurements with absolute photon flux determination coming dσ/dΩ Beam polarization Target polarization *Work at ASU is supported by the U.S. National Science Foundation 24

  25. New CLAS γ p →η' p Results • SAPHIR (Blue points) • CLAS (Black points) • SAPHIR used indirect method for photon flux • SAPHIR used a branch to determine η' and had only ~1% acceptance • CLAS η' results were obtained in similar manner as the CLAS π0 results *Work at ASU is supported by the U.S. National Science Foundation 25

  26. New CLAS γ p →η' p Results • Solid line: Nakayama and Haberzettl • Dashed line: Model inspired by A. Sibertsev • Solid line →Nakayama, Haberzettl: • Relativistic meson-exchange model • s-channel j=1/2 and j=3/2 resonances • t-channel ρ, ω exchange • Nucleon exchange in s- and u-channels • Contact current to make gauge-invariant • Dashed line → Sibertsev/Dugger: • Relativistic meson-exchange model • s-channel j=1/2 resonances • t-channel ρ, ω exchange • Nucleon exchange in s- and u-channels *Work at ASU is supported by the U.S. National Science Foundation 26

  27. Some π and η Photoproduction Models γ • MAID: • Isobar resonances • Born terms • t-channel ρ, ω exchange • Newly Reggeized for higher energy data γ • Anisivich, Klempt: • Resonances are Breit-Wigner except for two channel K matrix for S11(1535) and S11(1650) • Reggeized t- and u-channel • Coupled channels (dσ/dΩ and Σ: π+ n, π0 p, η p, K Λ,K Σ) • Li, Saghi: • Chiral constituent quark model • SU(6) x O(3) symmetry broken by gluon exchange γ 27

  28. Red: π+ n and π0 p • Blue: η p • LS: Li, Saghi • AK: Anisovich, Klempt • S11(1650) causing • difficulty in determining width for the S11(1535)? • Missing resonance D15(2070) found? • Exotic at 1800 MeV? 28

  29. Conclusions/What’s Next π0, π+, η, and η'photoproduction off the proton • World database greatly enhanced during past several years • Evidence that a missing D15(2070) resonance may have been found • Need for more polarization observables and coupled channel analyses to constrain the theoretical models • More data coming, including double polarization observables from CLAS in 2007 *Work at ASU is supported by the U.S. National Science Foundation 29

  30. Acknowledgements • NSF • ASU Group Members • J. Ball • P. Collins • E. Pasyuk • B. Ritchie • CLAS Collaboration • Theoretical curves for η' • Kanzo Nakayama • Helmut Haberzettl • New data from GRAAL • Annalisa D’Angelo • Dominique Rebreyand • Carlo Schaerf *Work at ASU is supported by the U.S. National Science Foundation 30

More Related