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Beam Background at Super-KEKB/Belle

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  1. Beam Backgroundat Super-KEKB/Belle Osamu Tajima (KEK) Apr 21, 2005 2nd Joint Super B factory work shop

  2. Outline • Status of KEKB / Belle (~ 2004 summer) • Super KEKB / Belle • How much increase ? • How do we reduce them ? • To be discussed for each bkg-types • Summary

  3. Belle Detector Detector will be upgrade to work under BGx20 SVD will work under BGx30 (rbp: 1.5  1.0 cm) Almost same structure PID 3.5 GeV (LER) ECL 8.0 GeV (HER) CDC KLM SVD

  4. Beam backgrounds should be concern • Synchrotron Radiation (SR) photons • generated in upstream magnets • generated in downstream (QCS) magnet • Shower caused by spent particles • beam-gas scattering • Touschek scattering • Radiative Bhabha origin • Neutrons from downstream beam line • Showers caused by over bend beams

  5. SR from upstream magnets SVD1.0 killer source (1999)

  6. SR from upstream magnets BGaIHER few % of SVD BG Negligible for others SVD1.0 killer source (1999)  Not serious after limitation of steering

  7. SR from QCS backscattering SR, downstream magnet (QCS) origin SVD ~ 1/3 of bkg CDC ~ 1/3 of bkg BGaIHER • Downstream final focus magnet (QCS) generate high energy SR (Ecrit ~ 40 keV) • SR photons are scattered at downstream chamber (~9m) • Backscattering photons enter to the detector (Eeff ~ 100 keV)

  8. Shower caused by Spent Particles due to beam-gas scattering due to Touschek scattering (intrabeam scattering) Dominant BG (except for KLM) BGbeam-gas = a PHERx IHER + b PLERx ILER BGToucheka ILER x ILER(sTouchecka E-3)

  9. Study for Contribution of Touschek Smaller beam-size (larger density)  larger background background If no Touschek KEKB Collision Contribution ~ 20 % of LER BG from particle showers

  10. Radiative Bhabha origin Main BG source for KLM Negligible for others BGaLuminosity

  11. KLM : EndCap Main bkg source is luminosity origin Luminosity component ~ 75 % Beam current component ~ 25 % rate (Hz/cm2) rate (Hz/cm2) FWD FWD BWD LER current (A) HER current (A) Luminosity (1034/cm2/s) layer8 layer9 layer10layer11 inner outer

  12. outside inside g 0 1 2…14 What is KLM bkg ? • Strong correlation with Luminosity • Long attenuation length from outer to inner FWD EndCap Not EM showers ! neutron Might be neutron

  13. 2.2 1.8 1.6 1.5 fast neutron (mSv/2weeks) 0.8 489 565 EM showers (counts/sec) 286 0 11 81 g-ray Rad-Bhabha (?) 534 472 99 222 ~5 m 152 ~10 m ~15 m Oct 27,2004 (by K.Abe & T.Sarangi) LER / HER = 1630 / 1160 mA Where is neutron source? Radiative-Bhabha might be origin HER LER Apr, 2003 (by Tawara, Nakamura)

  14. BG components 1st layer

  15. BG Estimation & Reductionfor Super-KEKB/Belle

  16. Backscattering of QCS-SR • Larger current and critical energy gives larger QCS-SR wattage  x6 (179 kW) • IR chamber design is the most important to suppress this background

  17. Kanazawa (KEKB) at HLWS Nov,04 HER SR:179 kW Solenoid IP LER HER ducts avoid SR !! SR hits over there Kanazawa (KEKB) at KEKB review Feb,05

  18. Backscattering of QCS-SR • Larger current and critical energy gives larger QCS-SR wattage  x6 (179 kW) • SR will be scattered at same region as current KEKB (~9m) • IR chamber design is close to final • 6 times higher than current SR-BG Dose at 1st layer of SVD • 400 kRad/yr at inner side of the ring • 130 kRad/yr at outer side of the ring

  19. Shower of Spent Particles • Beam-Gas scattering origin • HER / LER currents: 1.2/1.6 A  4.1/9.4 A • x4 Worse Vacuum : 1~1.5x10-7 Pa  5x10-7 Pa • x13.6 (HER), x23.6 (LER) higher contribution • Touschek origin • Almost same effective beam size ~ 0.88 ( 1/2 @IP) • shorter bunch length ~ 3mm/7mm • higher bunch current ~ 1.51 times • many #bunch ~ 3.9 times • Uncertainty of dynamic aperture  factor 2 uncertainty for Bkg • currently just 10% of total BG • x(23.5~41) higher contribution (bunch current)^2 / (beam volume) x #bunch

  20. Shower of Spent Particles • Beam-Gas scattering origin • HER / LER currents: 1.2/1.6 A  4.1/9.4 A • x4 Worse Vacuum : 1~1.5x10-7 Pa  5x10-7 Pa • x13.6 (HER), x23.6 (LER) higher contribution • Touschek origin • Almost same effective beam size ~ 0.88 ( 1/2 @IP) • shorter bunch length ~ 3mm/7mm • higher bunch current ~ 1.51 times • many #bunch ~ 3.9 times • Uncertainty of dynamic aperture  factor 2 uncertainty for Bkg • currently just 10% of total BG • x(23.5~41) higher contribution (bunch current)^2 / (beam volume) x #bunch

  21. 2.2 1.8 1.6 1.5 fast neutron (mSv/2weeks) 0.8 489 565 EM showers (counts/sec) 286 0 11 81 534 472 99 222 ~5 m 152 ~10 m ~15 m Rad. Bhabha : KLM Lsuper-KEKB / LKEKB = 25 / 1.3 ~ 19 times higher HER attenuation of neutron LER Material thickness (cm) Reduced by neutron shield  ~0.1 w/ 12cm thickness of “Epo-night” (Hazama co.)

  22. Radiative Bhabha : inner detectors • Actually, BaBar has large BG for inner detectors while it is negligible at Belle BaBar DCH We should consider because higher lum gives higher BG

  23. Difference of magnet position is the reason Shower caused by over bend particle Pointed out by M.Sallivan in 6th HLWS (Nov,2004)

  24. Simulation ~4 % of total BG Asuuming L=1034 /cm2/s Rad. Bhabha BG at ECL, NOW Barrel BWD EndCap FWD EndCap Data L=1.39x1034 /cm2/s HER = 1.19 A LER = 1.57 A

  25. Rad. Bhabha BG sim. for Super-KEKB Barrel BWD EndCap FWD EndCap Realistic design based on discussion with QCS group Expected BG from other sources with heavy metal total 1~2 ton L=25x1034/cm2/s ~4 % of total BG L=1034 /cm2/s

  26. Average Vacuum 5x10-7 Pa Super-KEKB design at Nov,2004 KEKB Rad. Bhabha mask around QCS magnet SR bkg reduction (~1/5) due to the improved IR chamber design 1st layer

  27. Average Vacuum 5x10-7 Pa Super-KEKB design at Now!! KEKB 1st layer

  28. CDC leak current 2005 2004 LER HER Beam current (mA) Part of the HER ring pressure (Pa)

  29. My optimistic Average Vacuum 2.5x10-7 Pa KEKB Super-KEKB design at Now!! Suppressed by Neutron shield BGx33 (several MRad/yr)!? (sim. for particle shower) Beampipe radius 1.51cm 1st layer

  30. Summary • We found solution to suppress QCS-SR and Radiative Bhabha origin backgrounds • Design of neutron shield for KLM should be determined • Vacuum level is the most important • Original design (5x10-7 Pa) • w/ further effort (2.5x10-7 Pa)  BG may be ~2/3 • Increasing of Touschek origin BG • Smaller bunch size & higher bunch currents are reason • Might be reduced by further study • Super KEKB Bkg  x 10~30 than KEKB • Beampipe radius 1.5cm  1cm • Further simulation study is important • Is there strong merit for physics ??

  31. Does the background scale with luminosity or just beam current ? CDC leak current Lum. (/ub/sec)

  32. backup

  33. Machine parameters for BG estimation

  34. Past trouble is reproduced by SR sim. actual orbit azimuthal angle dist. 1999 summer T.Abe (KEK) Steering angle was critical No more trouble w/ limitation of steering magnet SR BG killed SVD !!

  35. SR from upstream magnetssimulation for SVD 1st layer QC1L(-3m) duringinjection ~20 kRad/yr Deposit dose is localized on 1st layer of SVD But, still lower than others QC2L(-7m) at stored ~40 kRad/yr ~100 kRad/yr

  36. SR Particle-BG SVD BG Extraction

  37. Azimuthal angle dist. of SRat 1st layer of SVD Single-Bunch 15 mA (trigger-timing is adjusted) Total 0.8 A w/ 1284 bunch (random timing) Simulation for SR-backscattering simulation 63 kRad/yr HER 1.2A

  38. Azimu. angle dist. of Shower particlesat 1st layer of SVD HER single beam 0.8 A LER single beam 1.5 A data data simulation simulation Almost consistent with simulation ~40% accuracy

  39. SR Particle HER Particle LER 20% 24% 56% 16% 42% 42% BG of SVD at 1st layer SR ~ 1/3 Particle ~ 2/3 outer side 180 kRad/yr HER 1.2A LER 1.6 A LER inner side 170 kRad/yr

  40. KLM : Barrel Main bkg source might be luminosity origin Luminosity component ~ 70% Beam current component ~ 30 % rate (Hz/cm2) LER current (A) HER current (A) Luminosity (1034/cm2/s) layer0 layer1 layer2layer3 inner outer

  41. Now • HER / LER = 1.2 / 1.8 A • Luminosity ~ 13 /nb/sec (1.3x1034 /cm2/sec) • Which is dominant background? • SVD : SR ~ 1/3, Spent particles ~ 2/3 • CDC : SR ~ 1/4, Spent particles ~ 3/4 (HER ~ 1/4, LER ~ 2/4) • KLM EndCap : L~ 75 %, Spent particles ~ 25 % Barrel : L ~ 70 %, Spent particles ~ 30 % • Others : Spent particles might be dominat

  42. 2 1 IHER (A) 0 2 ILER (A) 0 Lumi. (/nb/sec) 60 30 0 2004 05 06 07 08 Near Future Prospects of KEKB Now (2004) L = 13 /nb/sec HER / LER = 1.2 / 1.8 A RF limits beam-current RF repair & minor upgrade (2005) within 3~4 years … Beam current : x 1.7 higher Luminosity : x 4.6 higher Assumption LER = 1.5xHER L = bIHER factor b increase 10% every year Crab cavity (2006) HER&LER  twice luminosity !? Minor upgrades (2007-2008)  L = 60/nb/sec HER / LER = 2 / 3 A

  43. SR (a IHER) Spent particles (aI2) Luminosity origin (aL) SVD outer x 2.6 inner x 2.3 CDC x 2.5 KLM EndCap x 4.2 Barrel x 4.1 Others x 2.8 Near Future If we can keep good vacuum ( optimistic case ) If we can keep good vacuum ( optimistic case ) most of detectors x 1.7 KLM x 3.9 lower limit !? 3 times bkg is good target value for near future

  44. Summary Higher bkg study must be needed for ~3 year later KLM bkg reduction must be start as soon as possible

  45. Beam Current dep. of Vacuum was reproduce by its dep. of BG NSR a I(A) Nparticlea I(A) x P(Pa) Nparticle/NSRa P(Pa) Average Pressure in upstream of HER

  46. Azimu. angle dist. of Shower particles simulation 106 kRad/yr 88 kRad/yr at HER 1.1A 86 kRad/yr at LER 1.6A simulation 42 kRad/yr data data simulation simulation HER single beam 0.8 A LER single beam 1.5 A

  47. Azimu. angle dist. of Shower particles w/ correction of Touschek simulation 106 kRad/yr 88 kRad/yr at HER 1.1A 44 86 kRad/yr at LER 1.6A simulation 42 kRad/yr 36 data data simulation simulation HER single beam 0.8 A LER single beam 1.5 A

  48. SVD Cluster Energy Spectra in Single Beam Run (1st layer) Energy deposition  Radiation dose HER(e-) 0.8 A LER(e+) 1.5 A SR and Particle-BG Only Particle-BG

  49. E-spectrum of HER Particle-BG • Diff. btw vacuum • bump on/off in HER • LER 1.5 A HER E-spectrum of particle BG is same as LER !! #clusters/keV/event Can measure SR and particle-BG separately energy (keV)

  50. Variation of Pressures at Pump pressure ( x10-8 Pa ) monitor limit * Maximum value