1. Beam Background Simulation at Belle/KEKB Motivation SR background Particle background Feedback to the detector design SR alarm Summary O. Tajima (Tohoku university) Belle Collaboration

2. Motivation Detector had serious radiation damage at the beginning of the experiment (SVD 1) Beam BG simulation is essential to  Understand the reason of rad. damage  Feedback to the design of the detector  Control of the BG level & accelerator operation criteria

3. Beam-induced Backgrounds Synchrotron Radiation (SR) BG from HER Soft SR : radiated at HER upstream Hard SR : backscattering photon (BS-photon) E crit ~ 40 keV E crit ~ keV Particle BG from HER and LER Beam-gas scattering in the entire ring (Bremsstrahlung and Coulomb) Touschek effect

4. SR Background (1) SR wattage calculation based on orbit Background simulation is performed by using EGS4 & Geant4  HER contribution is only considered  SR intensity & spectrum from each magnets  E crit ~ keV  Exact geometry of beam-pipe is integrated  Photons traced down to 1 keV (0.25keV for G4)  Reliable EM interactions (L-edge X-rays of Au etc.)

5. SR Background (2) SVD gain was droped for 10 days !

6. SR Background (3) The reason is the SR from HER !! Estimated dose w/ actual orbit condition at 1st layer (kRad/10days) < 200 Radiation hardness of SVD 1.0 270 Scattering at LER-side mask (BC3) 23 Soft SR (QC2) 62 Scattering at LER-side mask (QC2) 480 Scattering at LER-side mask (QC1)  Bad orbit condition cause it !!

7. SR Background (4) φ- dependence is reproduced by the simulation !  φ- dependence  dose HER

8. SR Background (5) Set the limit for kick angle of steering magnet ! Au coating is also effective !

9. Particle Background (1) 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 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 on CO at 1 nTorr

10. Particle Background (2) IP 8.3 m 6.5 m Belle

11. Particle Background (3) Comparison with measurement based on Single-Beam run (Dec 2000) data Simulation Brems+CoulmbTouschekTotal HER2440.5---40.5 LER82 35.2 (23.3) 56.5 (6.5) 91.7 (29.8) Dose on 1st layer (kRad/yr) The values in “(…) “ means no contribution from scatterings on materials outside the vacuum chamber Reproduce the measurements !

12. SVD2 (1) 2cm1.5cm

13. SVD2 (2)

14. Particle BG on SVD2 (1) SVD1.4 r = 2 cm SVD2 r = 1.5 cm SVD2* r = 1cm 1st Layer3 cm2 cm1.5 cm HER Brem 5.912.527.5 HER Coul34.613.435.1 LER Brem20.413.167.2 LER Coul14.814.051.5 Touschek56.528.8474 Sum13282655 (kRad/yr)

15. Particle BG on SVD2 (2) better SVD2* (r=1cm) SVD1.4 (r=2cm) SVD2 (r=1.5cm)

16. Soft SR BG on SVD2 (1) Based on the two orbits

17. Soft SR BG on SVD2 ( ２ ) Dose during the Physics-run (kRad/yr) A few kRad/yr during physics runs 2001.11.07 2002.05.15 QC1LE<< 0.001< 0.001 QC2LE< 0.08< 0.008 ZHQC2< 0.26< 0.005 BC1LE< 0.242.2±0.3(bottom)  x = 24nm,  y /  x = 3%,  * x /  * y = 63 / 0.7cm

18. Soft SR BG on SVD2 (3) Dose during the Injection (kRad/yr) A few kRad/yr during injections 2001.11.07 2002.05.15 QC1LE0.86±0.07 (top)0.84±0.07 (top) 1.46±0.10 (bottom)1.56±0.10 (bottom) QC2LE0.022±0.001 (top)0.016±0.003 (top) 0.023±0.002(bottom)0.027±0.004(bottom) X offset = 10mm,  x = 0.9mm

19. Hard SR on SVD2 (by Geant4 / EGS4) 20 ~ 30 kRad/yr (?) E deposit B.S. -SR Hard-SR Cu compton K-edge of Cu K-edge L-edge of Au Preliminary

20. Expected Dose on SVD2 Lower BG than till now (~2/3) Better VTX resolution is expected Higher tracking efficiency Stable data taking for a long time Particle BG  ~80 kRad/yr SR BG  20~30 kRad/yr Total ~100 kRad/yr Will be checked by real operation from Oct

21. SR alarm(1) Online alarm system based on the SR-sim.  Bad operation condition is rejected  Control the SR BG level  Challenging accelerator operation 1. Real orbit calculation from the beam position monitor, BPM (  =100  m) 2. Calculation of SR wattage distribution 3. SR background estimation

22. SR alarm(2) Real orbit is calculated by  2 fitting with IP constraint (<1mm)

23. SR alarm(3) Performance Getting BPM values (13BPMx3)~ 0.1 sec Getting magnets info (22 k 0 -values)~ 1 sec Orbit fitting~ 0.1 sec Wattage (BG) sim into the detector ~ 1 min (to be < 5 sec) System is almost ready ! To be installed soon !

24. Summary Understand reproduce the study / experience on SVD1 Feedback Detector / orbit was designed based on sim.  lower radiation damage ! (~100 kRad/yr)  can be checked soon for SVD 2 ! Control Alarm system using real time SR sim based on actual orbit  start soon ! Simulation of Beam BG (SR & Particle)