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Current Understanding of Beam-Induced Background at Belle

Current Understanding of Beam-Induced Background at Belle. Osamu Tajima (Tohoku univ.) for many people. Contents. Backgrounds which we are considering Simulations Particle scatterings, SR Backgrond WS in SLAC, Sep 2003 Super B WS in Hawaii, Jan 2004 Measurements

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Current Understanding of Beam-Induced Background at Belle

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  1. Current Understanding of Beam-Induced Backgroundat Belle Osamu Tajima (Tohoku univ.) for many people

  2. Contents • Backgrounds which we are considering • Simulations • Particle scatterings, SR • Backgrond WS in SLAC, Sep 2003 • Super B WS in Hawaii, Jan 2004 • Measurements • SR / scattering by residual gas / Touschek • Super B WS in Hawaii, Jan 2004 • Study for luminosity related backgrounds • During Continuous-Injection • Summary new

  3. Considered Backgrounds Particle Background Showers from scattered beam particles by Residual Gas or intra-beam scattering Brem. Coulomb Touschek Synchrotron Radiation (SR) Soft-SR (several keV) Generated by upstream magnets Hard-SR ( keV ~ 150 keV) Backscattering from downstream, originally generated in QCS magnets

  4. Hard-SR : Backscattering of SR Scattered at downstream photon-stop (OC2RE chamber) HER e- High energy SR is generated in OCS magnet

  5. Background Simulations by T.Abe • Soft-SR (~1 kRad/yr) • based on actual orbits which are calculated by the fitting of beam-position-monitors with IP costraint (<100um) • SR are generated for each magnets • Most of BG comes from QC1 magnet (~3m upstream) • Hard-SR (58 kRad/yr) • using design orbit, beam-size and distortion of orbit is considered • blowup of beam-size gives several % bkg rise

  6. Particle Background Simulation by K.Trabelsi TURTLE + GEANT simulation TURTLE : simulation in the ring • Tool for beam transport & beam-gas scatterings • The entire ring, up to one whole turn • Bremsstrahlung & Coulomb scattering • w/ assuming 1 nTorr CO pressure GEANT : simulation in / around the detector • Full detector simulation based on Geant3 • 8.3 m HER / 6.5 m LER sides (up to QC2 magnets) • Magnetic fields of Quads and solenoids are included

  7. Particle Background Simulation Belle 8.3 m 6.5 m IP

  8. Background Measurements Already talked at Super B WS in Hawaii, Jan 2004

  9. SR Particle-BG Extract Two-types BG Separately Energy spectrum of SVD Energy spectrum Energy deposition Radiation dose

  10. Reproduce of Vacuum change NSR a I(A) Nparticlea I(A) x P(Pa) Nparticle/NSRa P(Pa) Average of HER whole ring Average of HER upstream

  11. Azimuthal Distribution of SR Single-Bunch 15 mA (trigger-timing is adjusted) Total 0.8 A w/ 1284 bunch (random timing) Hard-SR simulation 66 kRad/yr at HER 1.1A FWD BWD 42 kRad/yr at HER 1.1A simulation 58 kRad/yr Only above threshold 10 keV Simulation complements below threshold

  12. Azimuthal Distribution of Particle BG FWD BWD 88 kRad/yr at HER 1.1A simulation 106 kRad/yr HER 0.8 A 86 kRad/yr at LER 1.6A simulation 42 kRad/yr LER 1.5 A

  13. Study of Touschek Effect Smaller beam-size (larger density)  larger background background If no Touschek Single beam run Collision run Touschek contribution < 20 % at collision ~ 50 % at single beam 31 % in simulation Beam-size is different for collision Touschek contribution must be corrected

  14. Azimuthal Distribution of Particle BG w/ correction of Touschek FWD BWD 88 kRad/yr at HER 1.1A simulation 106 kRad/yr HER 0.8 A 44 86 kRad/yr at LER 1.6A simulation 42 kRad/yr LER 1.5 A 36

  15. f ~ 0 deg f ~ 180deg total SR simulation Particle-BG (HER, e-) measurement Particle-BG (LER, e+) 160 120 80 40 0 40 80 120 160 radiation dose (kRad/yr) Measured BG is consistent with Simulation Radiation Dose at SVD 1st layer

  16. Extrapolated Occ.  single beam runs At Maximum Currents (HER 1.1A, LER 1.6A) Collision (Dec2003) ~12 % ~11 % Indication of Low Beam-beam effects

  17. Search for Luminosity related backgrounds

  18. Luminosity Dependences • Change of room temperature • around RF • Luminosity decrease • No change for currents, life-times, vacuums, size… Good situation to check the Luminosity related backgrounds

  19. Luminosity Dependences SVD occ. were not change ! 2nd layer 1st layer 3rd layer 4th layer

  20. Luminosity Dependences CDC BG was not change!

  21. Luminosity Dependences No significant change for TOF rate

  22. by T.Tsukamoto Luminosity Dependences ECL rate no change ! FWD Endcap BWD Endcap Barrel

  23. 100 efficiency (%) 80 0.2 0.5 hit rate (Hz/cm2) Luminosity Dependences No change for Endcap KLM !? efficiency drop may dilute correlation

  24. No correlation for Barrel KLM ! Luminosity Dependences

  25. by K.Abe et al Luminosity Dependences we put the scintillation detector 12x12cm2 KLM Its bkg has strong correlation with luminosity ( next page)

  26. HER current luminosity background LER current

  27. During Continuous-Injection • Basically, monitored by CDC leak currents, PIN and trigger rates • Trigger rate is too high ~ 2 msec  DAQ veto 3.5 msec after each injections • Usually, ~10% higher BG than stored @ CDC • Sometimes, higher  +20~30% or more • Depends on position of movable-mask and accelerator condition • Based on experiences for the reduction • Tuning of movable-masks in rings, energy spread of injection beam etc can reduce it

  28. Summary • Simulation - Measurements are consistent ( If Touschek contribution is corrected ) ~ 800 Rad/day • Beam-Beam effects looks low • No observation of luminosity related BG’s for all sub-detectors except for test detector (KLM may have correlation !?) • Trying to understand for injection related • Movable-mask study may be important issue • Study for Linear-acc. is also important

  29. Backup

  30. SVD occ. Inner most layers

  31. by J.Flanagan Luminosity Dependences Loss monitor was put on the wall KLM No correlation was observed

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