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π 0 -threshold measurements ( unpol. photons )

π 0 -threshold measurements ( unpol. photons ). Date : Sep-Oct 2007. Ebeam: 450.0 MeV. E γ : 130 – 420 MeV. NMR : 0.539456(run1), 0.538114 (run2). σ tot ( γ +p p+ π 0 ) run 1 & SAID. σ tot  σ tot * 1.05. σ tot ( γ +p p+ π 0 ) run 1 & SAID. two regions:

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π 0 -threshold measurements ( unpol. photons )

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  1. π0-threshold measurements(unpol. photons) • Date : Sep-Oct 2007. • Ebeam: 450.0 MeV. • Eγ: 130 – 420 MeV. • NMR : 0.539456(run1), 0.538114 (run2).

  2. σtot (γ+pp+π0)run1 & SAID σtot σtot * 1.05

  3. σtot (γ+pp+π0)run1 & SAID two regions: high & low Eγ

  4. σtotat low & high Eγ low Eγ: shift ~ -2 MeV high Eγ: shift ~ +4 MeV

  5. Moeller scattering

  6. Background for Moeller:Triplet Electroproduction σ ~ Z2 two electrons – in Tagger, a positron – out.

  7. Detection of Moeller electrons in Tagger • Coincidence of two electrons: | T1 – T2 | < 1 ns • Difference of electrons energies: | E1 - E2 |> 10 MeV

  8. Moeller in Tagger

  9. 6 MeV shift of Moeller peak

  10. Tagger channel vs Moeller peak

  11. 3.5 MeV shiftin 2007 Jul2007, 1508 MeV Oct2007, 883 MeV

  12. 2.3 MeV shift in Jun2004(π0-threshold, linpol) radiator = Diamond Ebeam = 450 MeV

  13. Old Tagger measurements Radiator = Diamond Ebeam = 882 MeV Jul04, Sep04, Dec95

  14. shifted CB-data, SAID & MAID Control region: 165 – 175 MeV Shift: ~ 2 MeV

  15. shifted CB-data & TAPS Dec95 Fine step photon energies: no Microscope, just change Tagger field TAPS-95 : A.Schmidt, Mainz

  16. CB-data, SAID & MAIDnear threshold γ+pp+ξ (ξ γ γ ) Ethr=147.5 +/- 0.5 MeV  mξ=137.5 +/- 0.5 MeV

  17. Investigation of Taggerwith Moeller scattering • Tagger channels: 1 – 352. • Ebeam: 180, 450, 883, 1508 MeV. • Radiator: Diamond. • Beam current: 1nA, 10nA, 50nA.

  18. Attenuationlength of NaI PM AmBe ΝαΙ Eγ=4.44 MeV

  19. Attenuation length of NaI PM AmBe ΝαΙ AmBe Eγ=4.44 MeV

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