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The η - mass measurement with the Crystal Ball at MAMI

The η - mass measurement with the Crystal Ball at MAMI. A. Nikolaev for the Crystal Ball @ MAMI and A2 Collaborations Helmholtz Institut f ür Strahlen - und Kernphysik, University Bonn. The h mass measurement at MAMI. The h production threshold measurement from γ p → p η .

lucretia-armando
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The η - mass measurement with the Crystal Ball at MAMI

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  1. The η-mass measurement with the Crystal Ball at MAMI A. Nikolaev for the Crystal Ball @ MAMI and A2 Collaborations Helmholtz Institut für Strahlen- und Kernphysik, University Bonn

  2. The h mass measurement at MAMI • The h production threshold measurement fromγp→pη. • The mass of h is calculated from relation: where mp is the proton mass, Egthr – production threshold. • Recently published measurements: CB Meeting, Basel 10/5/06

  3. Crystal Ball/TAPS detector Particle identification detector Crystal Ball 672 NaI detectors • Crystal Ball detector: • 672 NaI crystals • measures EγandӨγ TAPS 510 BaF2 detectors • Particle identification detector: • 24 plastic bars of size 30 cm x 2 cm 0.2 cm • marks charged particles • Forward wall detector TAPS: • 510 BaF2 single plastic detectors with individual vetos CB Meeting, Basel 10/5/06

  4. The tagging facility • The energy Eg of the photon is determined (tagged) by: • Incoming MAMI electron beam energy E0 is known with an accuracy of sE0 = 68 keV. • Scattered electron energy Ee-is known with an accuracy of sEe- = 78 keV. CB Meeting, Basel 10/5/06

  5. Tagger microscope detector • An array of 96 plastic scintillator fibres (3 mm x 2 mm). • Each single fibre overlaps by 1/3 with its neighbor. The overlap region defines microscope detector channel μch(191 channels in total). • The energy resolution is 0.3 MeV per microscope channel μch. • Tagger microscope is positioned to cover electron energies 153 to 209 MeV. At a beam energy of 883 MeV this corresponds to tagged photons between 674 MeV and 730 MeV (η threshold ~707 MeV). CB Meeting, Basel 10/5/06

  6. Tagger microscope energy calibration • Direct calibration: • Direct position measurement of the MAMI electron beam for the energies Ee- = 180.1 MeV, 195.2 MeV and 210.2 MeV using the same dipole magnetic field as in the experiment (Bcal = Bexp = 1.049 T). • Scan beam through microscope varying the dipole field: • Increase tagger dipole magnetic field Bcal in small steps. • Measure new electron beam position supposing equivalent electron beam energy for a given field setting Bcal : CB Meeting, Basel 10/5/06

  7. Tagger microscope energy calibration Blue arrows show direct position measurements of the electron beam of energies 180.1, 195.2 and 210.2 MeV. 210.2 MeV 1.055 T 195.2 MeV 1.049 T 180.1 MeV 1.049 T Expected η threshold CB Meeting, Basel 10/5/06

  8. Total energy measurement uncertainty • Standard deviation of data points from fit: was calculated for each scan individually: • Average uncertainty: s= 0.27 mch = 78 keV (electron energy Ee-). • Add electron beam energy E0 determination uncertainty of MAMI 68 keV (s) s(threshold) = 103 keV s(mh) = 65 keV CB Meeting, Basel 10/5/06

  9. The h mass beamtimes • Two beamtimes for the h mass measurement: CB Meeting, Basel 10/5/06

  10. Identification of h meson • h mesons are identified via their uncharged decay modes. • Events with 2 photons and 6 photons (with or without proton) are investigated. • Photons are identified with Crystal Ball/TAPS detector. • Particle identification detector serves as a veto for charged particles in CB. • TAPS crystals have individual veto detectors for marking charged particles. • h→2γ and h→3π0 decays are analyzed independently. Particle identification detector (PID) Crystal Ball 672 NaI crystals TAPS 510 BaF2 crystals with individual vetos CB Meeting, Basel 10/5/06

  11. Identification of photons and protons protons • Crystal Ball • Uncharged particles = photons. • Charged particles: ΔE(PID) vs. ECB: cut the proton. • TAPS forward wall • Vetos: charged particles. • Pulse shape analysis: cluster energy deposition in short Eshort vs. in long Elong integration interval. • Time of flight: ETAPS cl.vs.( tTAPS cl. – tCB photons ). protons, neutrons protons photons photons CB Meeting, Basel 10/5/06

  12. CB time walk correction • Investigate γp→pπ0with γγp final state. • For each of 672 NaI crystals: • ECB hitvs.( tCB photons – tPID proton ) • fit the peaks with t(E) function. • 7-13 Dec 2004 #4924-5088: • faulty crystals #: 168, 183, 194, 205, 221, 352. • 11-20 Jan 2005 #5200-5452: • faulty crystals #: 41, 168, 205. Ladder FWHM = 2.3 ns Sigma = 1.0 ns Microscope FWHM = 1.7 ns Sigma = 0.7 ns CB Meeting, Basel 10/5/06

  13. Invariant mass distributions Mean = 568 MeV Sigma = 20 MeV • 2g (with or without proton) final state invariant mass distribution. • 3p0 (6g, with or without proton) final state invariant mass distribution. • Cut on invariant mass distribution. • Time coincidence peak between tagger microscope and detector: cut the coincident events. • Cut on lost proton missing mass. Mean = 138 MeV Sigma = 8 MeV π0 η Mean = 558 MeV Sigma = 16 MeV FWHM = 1.7 ns Sigma = 0.7 ns CB Meeting, Basel 10/5/06

  14. Tagger dipole field / Jan 2005 • NMR = 1.049057±0.000535 T (± 0.01 MeV in Ee). Very good! CB Meeting, Basel 10/5/06

  15. Tagger dipole field / Dec 2004 • NMR = 1.049527±0.015 T (± 2.78 MeV in Ee). • Need to refine data with faulty NMR! CB Meeting, Basel 10/5/06

  16. Microscope channel efficiency • Investigate γp→pπ0with 2 photons and 1 proton final state using tagger. • Prompt - random time windows. • In microscope region (tagger channels 55-85) “pion yield” looks constant. • Investigate the same with microscope. • Microscope channels have different efficiencies! • Use “pion yield” distribution as microscope channels efficiency to correct the η yield! Microscope region pion yield in microscope pion yield in tagger CB Meeting, Basel 10/5/06

  17. Eta yield for reaction γp→pη (η→2γ) Fit function: f(x)=a0+a1 x+a2 x2+a3 x3 η→2γ Fit range: 0-75 μch Without acceptance correction! Eγ CB Meeting, Basel 10/5/06

  18. Eta yield for reaction γp→pη (η→3π0) Fit function: f(x)=a0+a1 x+a2 x2+a3 x3 η→3π0 Fit range: 0-75 μch Without acceptance correction! Eγ CB Meeting, Basel 10/5/06

  19. Result dependence on fit range η→2γ η→3π0 Fit range: 0 to 75 μch 10 to 75 μch 20 to 75 μch 30 to 75 μch 40 to 75 μch 50 to 75 μch 60 to 75 μch 70 to 75 μch Fit range: 0 to 75 μch 10 to 75 μch 20 to 75 μch 30 to 75 μch 40 to 75 μch 50 to 75 μch 60 to 75 μch 70 to 75 μch • 1. η→2γ: mη=547.683 ± 0.013fit MeV • 2. η→3π0:mη=547.743 ± 0.013fit MeV Very preliminary CB Meeting, Basel 10/5/06

  20. Conclusions • New threshold data on γp→pη. • Theη identified by η→ γγ and η→3π0. • Energy calibration for Ee- (tagger microscope) done. • Energy calibration E0 (Mainz Microtron) final checks for systematical error underway. CB Meeting, Basel 10/5/06

  21. RTM 3 B = 1.3260 T ±0.13 mT ΔE = ~7.81 ±0.02 MeV D73 = 3768.45 ±0.4 mm MAMI energy determination uncertainty turn 90 Cavity 1 Dipole 1 Dipole 2 turn 73 Cavity 2 where e is electron charge, B is dipole magnetic field, D - electron track diameter. D73 ΔE Eout = Ein + z·ΔE, z = 90 Ein = 180 MeV Extrapolate to end energy: Eout = 883.X ± 0.16 MeV (FWHM) σEout= 68 keV E73 = 751.649 ± 0.107 MeV CB Meeting, Basel 10/5/06

  22. Proton missing mass distributions gp→ph Microscope Microscope g p→ph (h→2g) g p→ph (h→3p0) hits hits Missing mass / MeV Missing mass / MeV Main tagger Main tagger g p→ph (h→3p0) g p→ph (h→2g) hits hits Missing mass / MeV Missing mass / MeV CB Meeting, Basel 10/5/06

  23. Photon beam position Jan 2005 CB Meeting, Basel 10/5/06

  24. The h mass beamtimes • Two beamtimes for the h mass measurement: CB Meeting, Basel 10/5/06

  25. MAMI energy measurements CB Meeting, Basel 10/5/06

  26. Result dependence on fit range η→2γ η→3π0 Fit range: 0 to 75 μch 10 to 75 μch 20 to 75 μch 30 to 75 μch 40 to 75 μch 50 to 75 μch 60 to 75 μch 70 to 75 μch Fit range: 0 to 76 μch 10 to 76 μch 20 to 76 μch 30 to 76 μch 40 to 76 μch 50 to 76 μch 60 to 76 μch 70 to 76 μch • 1. η→2γ: σ = 0.023 MeV (in mη) • 2. η→3π0:σ = 0.025 MeV (in mη) • Function fits the points very good! 0.1 MeV CB Meeting, Basel 10/5/06

  27. Result dependence on fit range η→2γ η→3π0 Fit range: 0 to 75 μch 10 to 75 μch 20 to 75 μch 30 to 75 μch 40 to 75 μch 50 to 75 μch 60 to 75 μch 70 to 75 μch Fit range: 0 to 75 μch 10 to 75 μch 20 to 75 μch 30 to 75 μch 40 to 75 μch 50 to 75 μch 60 to 75 μch 70 to 75 μch • 1. η→2γ: σ = 0.023 MeV (in mη) • 2. η→3π0:σ = 0.100 MeV (in mη) • Function fits the points good! 0.1 MeV CB Meeting, Basel 10/5/06

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