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SPring-8 レーザー電子光 ビームラインでの タギング検出器の性能評価

日本物理学会 近畿大学 2000.4.1. SPring-8 レーザー電子光 ビームラインでの タギング検出器の性能評価. 核物理研究センター 三部 勉 LEPS collaboration. １．レーザー電子光 ２．タギング検出器 ３．実験セットアップ ４．エネルギー分解能 ５．検出効率とバックグラウンドレート ６．まとめ. Laser Electron Photon. Electron 8GeV. Laser 3.5eV. Backward Compton scattering. Scattered photon

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SPring-8 レーザー電子光 ビームラインでの タギング検出器の性能評価

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  1. 日本物理学会 近畿大学 2000.4.1 SPring-8レーザー電子光ビームラインでのタギング検出器の性能評価 核物理研究センター 三部 勉 LEPS collaboration １．レーザー電子光 ２．タギング検出器 ３．実験セットアップ ４．エネルギー分解能 ５．検出効率とバックグラウンドレート ６．まとめ

  2. Laser Electron Photon Electron 8GeV Laser 3.5eV Backward Compton scattering Scattered photon (Laser Electron Photon) Energy Max 2.4GeV Intensity 1×107 /sec Linear/Circular polarization

  3. Photon Energy（GeV） Position of Scattered electron（SSDch） Photon Tagging Measured by PWO calorimeter Photon energy Eg = Ee - Ee’ Initial electron energy Scattered electron energy Analyzed by Bending Magnet

  4. Tagging counter (top view) Timing Counter Energy Counter Plastic scintillator ×20 (3mm(T),7.4mm(W),10 mm(H)) Silicon Strip Detector ×2 (Analog readout,100mm pitch 640 ch) Accelerator chamber wall Scattered electron 1cm 8GeV electron beam

  5. LEPS spectrometer • Analyzing magnet (0.7T) • Vertex Detector (SSD) • Charged particle tracking • MWDC (3 chambers) • Particle Identification • TOF wall (40 slats)

  6. Tagging Counter Spectrometer（ e+e-） Eg Experimental Setup (Top view) Energy Resolution Tagging efficiency Background rate TOF Dipole Magnet（０．７T) e- Bremsstrahlung Photon Plastic Scintillator e+ Target （ Al ２mm width,１mm thick） ＋ Scintillation fiber （1mmf×２） MWDC

  7. e+e- Momentum Reconstruction • e+e- production point • → localized in wire target • sx , sz～ 0.3mm • One to one correspondence • pe xe E(Tagging) GeV Monte Carlo Simulation Dpe～ 8 MeV/mm @1GeV E（e+e-）GeV Pe : e+/e- momentum xe : e+/e- x-position after magnet

  8. Energy Resolution Energy resolution of Tagging 1.60<Eg<1.88 GeV sMeas=23MeV sg2 = sMeas2ｰ s e+e-2 Counts Monte Carlo Width of Experimental Data Resolution of momentum reconstruction Ave.15.3 MeV sg(MeV) ‐50 0 50 （MeV） E(Tagging) - E(e+e-) Systematic error Eg (GeV)

  9. Electron Track in Tagging counter qe Scattered Electron Plastic Scintillator Plastic Scintillator SSD Event Selection / Analysis 1. Pick up two clusters in up and down stream SSD. 2. Angle of track |qe - qe| < 4 s 3. Number of corresponding hit in the scintillator array (n) → Hit pattern ‘quality’ = 0 SSD+ Scintillator(n = 0) =1 SSD+ Scintillator(n = 1) =2 SSD+ Scintillator(n = 2)

  10. Hit pattern(quality) Efficiency Background rate 86.5± 0.6% 2.3 ± 0.1% SSD+ Scintillator(n = 2) 90.6± 0.5% 2.6 ± 0.1% SSD+ Scintillator(n ≧ 1) 91.0± 0.5% 2.8 ± 0.1% SSD+ Scintillator(n ≧ 0) Tagging Efficiency and Background rate Definitions Efficiency ＝ Number of tagger hit(≧1 track) ÷ Number of e+e- pair in Tagging acceptance Background rate ＝ Number of tagger hit(≧2 tracks) ÷ Number of tagger hit(≧1 track) Condition : Bremsstrahlung photon ＠maximum electron current

  11. Summary • Performance of Tagging system • 1. Experimental method • e+e- momentum reconstruction using wire target. • 2. Energy resolution • Photon Tagging Resolution 15 MeV • 3. Efficiency and background rate (Bremsstrahlung photon) • Efficiency 90% [SSD+ Scintillator (n ≧ 1)] • Background rate 3 %. • 4. Further study is on going with Laser Electron Photon ...

  12. Photon Energy Spectrum 1st beam observation (1999.July) Counts 1 2 3 Photon energy (GeV)

  13. Tagging counter PMT SSD Plastic Scintillator Beam

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