Current BG Status at Belle Osamu Tajima ( Tohoku univ ) Assumption in this talk 100days-operation / yr 1nTorr CO pressure in simulation HER / LER = 1.1 / 1.6 A in simulation

Contents Design concepts for BG reduction BG measurements  Radiation dose  Hit rate (SVD occupancy)  Layer (radius) dependence Comparison data and simulation  Support Super-KEKB / Belle design Ideas for Less BG

SVD Upgrade in 2003 summer r bp = 2.0 cm 3 layers Rad. hardness r bp = 1.5 cm 4 layers > 10 MRad (DSSD) > 20 MRad ( readout chip ) ~ 1 MRad  Better vertex resolution / tracking efficiency

SVD Upgrade for Super-Belle r bp = 1.5 cm Super-Belle Smaller r bp (1cm) Higher beam current Basic design is same as SVD2 beampipe We must understand Current Situation Success of beampipe design is key-point for Super-KEKB/Belle

Beam-BG on Belle-SVD2 Synchrotron Radiation (SR) Particle Background Showers from scattered beam particles by Residual Gas or intra-beam scattering Soft-SR (several keV) Hard-SR ( keV ~ 150 keV) Generated by upstream magnets Backscattering from downstream Brem. CoulombTouschek

Reduction of Particle-BG Particle BG ~ 70 kRad/yr

Reduction of Soft-SR Au-coating ! crescent shape SR-mask  some efforts

Reduction of Soft-SR Au-coating ! crescent shape SR-mask Au coating absorbs low energy photon less than 8 keV

Reduction of Soft-SR Au-coating ! crescent shape SR-mask Saw-tooth surface shape in Ta blind Soft-SR reflected on Ta

Reduction of Soft-SR Au-coating ! crescent shape SR-mask (~2.5mm) Crescent shape SR-mask blind Be section from Soft-SR

Reduction of Soft-SR Au-coating ! crescent shape SR-mask Soft-SR ~ few kRad/yr

Reduction of Hard-SR Scattered at downstream photon-stop (OC2RE chamber) HER e- High energy SR is generated in OCS magnet Put photon-stop far place (~9m) Chamber material: Cu Hard-SR ~ 29 kRad/yr

Beam-BG on Belle-SVD2 Synchrotron Radiation (SR) Particle Background Showers from scattered beam particles by Residual Gas or intra-beam scattering Soft-SR (several keV) Hard-SR ( keV ~ 150 keV) ~ 70 1 st layer few 1 st layer ~ 29 kRad/yr Generated by upstream magnets Backscattering from downstream Brem. CoulombTouschek

BG measurement and Comparison with simulation

SR measurement w/ Single-Bunch HER 15 mA, with adjusting trigger timing Can measure dose w/ hit-rate (0.2 % occupancy) and energy deposition (15 keV/ch)  ~20 kRad/yr 1.1 A (33 kRad/yr at max. position,  =180deg) ( contribution below th. is corrected by simulation) SVD 2.0 SVD 1.X data simulation

SVD Cluster Energy Spectra in Single Beam Run HER 0.8 ALER 1.5 A Can extract SR from spectrum shape !? Only Particle-BG SR and Particle-BG

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

Extraction SR in HER Single Beam 50 mA 100 mA 200 mA 400 mA600 mA800 mA HER Particle SR Hard-SR simulation

Correlation with Vacuum N particle /N SR  P(Pa) N SR  I(A) N particle  I(A) x P(Pa) Average of HER whole ring Average of HER upstream

Azimuthal Distribution of SR 33 kRad/yr at HER 1.1A 21 kRad/yr at HER 1.1A Only above threshold 10 keV Simulation complements below thereshold simulation 29 kRad/yr Single-Bunch 15 mA (trigger-timing is adjusted) Total 0.8 A w/ 1284 bunch (random timing) Hard-SR simulation

Azimuthal Distribution of Particle BG 44 kRad/yr at HER 1.1A 43 kRad/yr at LER 1.6A HER 0.8 A LER 1.5 A simulation 53 kRad/yr simulation 21 kRad/yr

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

Azimuthal Distribution of Particle BG 44 kRad/yr at HER 1.1A 43 kRad/yr at LER 1.6A HER 0.8 A LER 1.5 A simulation 53 kRad/yr simulation 21 kRad/yr 22 18

Radiation Dose at SVD 1 st layer At Maximum Currents: HER 1.1A, LER 1.6A Outer-direction ~ 0 degree Inner-direction ~ 180 degree Particle-BG (LER) 22 (18) kRad/yr 14 (11) kRad/yr Particle-BG (HER) 44 (53) kRad/yr 29 (33) kRad/yr SR-BG 17 (8) kRad/yr 33 (29) kRad/yr Total 83 (79) kRad/yr 76 (73) kRad/yr (…) is 1nTorr pressure Data and simulation is consistent Touschek contribution is reduced based on measurement

Radiation Dose at SVD 1 st layer At Maximum Currents: HER 1.1A, LER 1.6A Outer-direction ~ 0 degree Inner-direction ~ 180 degree Particle-BG (LER) 22 (18) kRad/yr 14 (11) kRad/yr Particle-BG (HER) 44 (53) kRad/yr 29 (33) kRad/yr SR-BG 17 (8) kRad/yr 33 (29) kRad/yr Total 83 (79) kRad/yr 76 (73) kRad/yr (…) is 1nTorr pressure Data and simulation is consistent Touschek contribution is reduced based on measurement Two parameters have large uncertainty (pressure, movable mask) It may happen that absolute values too well agree Consistency of azimuthal distribution is important

Radiation Dose at SVD 1 st layer At Maximum Currents: HER 1.1A, LER 1.6A Outer-direction ~ 0 degree Inner-direction ~ 180 degree Particle-BG (LER) 22 (18) kRad/yr 14 (11) kRad/yr Particle-BG (HER) 44 (53) kRad/yr 29 (33) kRad/yr SR-BG 17 (8) kRad/yr 33 (29) kRad/yr Total 83 (79) kRad/yr 76 (73) kRad/yr (…) is 1nTorr pressure Data and simulation is consistent Touschek contribution is reduced based on measurement We can trust simulations Its uncertainty for abs. may be factor a few

Constraint for Occupancy (hit-rate) At Maximum Currents (HER 1.1A, LER 1.6A) Outer-direction ~ 0 degree Inner-direction ~ 180 degree Particle-BG (LER) 3 % 2 % Particle-BG (HER) 7 % 5 % SR-BG 2 % 4 % Total (single beam) 12 %11 % Radiation Dose  Occupancy (cluster size: Particle-BG  3.5 ch, SR  1.5 ch) Collision 12 %11 %

Energy spectra for each layers LER single beam 1st r ~ 2cm 2nd r ~ 4.4cm 3rd r ~ 7cm 4th r ~ 8.8cm HER single beam

Layer dependence (single beam) Particle (LER)Particle (HER) SR BG  1/(r-r bp ), r bp : beampipe radius There may be correlation BG and 1/(r-r bp )

Other sub-detectors No large difference for BG (current diff. causes small diff. ?) No problem SVD 1.6 (Jun, 2003) SVD 2.0 (Dec, 2003) beampipe radius2.0 cm1.5 cm HER/LER1.0 / 1.5 A1.1 / 1.6 A CDC leak current 19  A21  A TOF rate20 kHz25 kHz EFC rate2.1 kHz2.2 kHz

Ideas for Less BG Improvement of vacuum HER: sensitive area is upstream (0~100 m) LER: sensitive area is whole ring How about not-straight path ? HER upstream is almost straight path Movable mask study Particle-BG 1/2 Particle-BG  ~ 2/3 total-BG/Occ. Put photon-stop far place  Detail will be discussed in “Belle SR” talk SR-BG (dominated by Hard-SR)

Summary Beampipe radius 2  1.5 cm (  1 cm) Dose level is smaller (100  80 kRad/yr) Consistent with simulation Measure SR & Particle-BG separately using energy spectrum of SVD SR contribution ~1/3 of total Touschek is low < 20 % of LER-BG BG may decrease  1/(r-r bp ) Success of beampipe design Strong support for design in Super-B Super-B This method is first time in the world !?

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Radiation Monitors 18 kRad/yr 80 kRad/yr 60 kRad/yr before 100 kRad/yr Dose on Si is consistent with monitor

Is monitors measuring SR ? Be pipe Outer-side of ring Inner-side of ring The 300  m Au on the manifold blinds SR-BG Backscattered Hard-SR BWDFWD Most of SR photons are absorbed by Au, and converted to lower energy photons (8~14keV) via the photoelectric effect e- Difficulty to measure SR Dose at DSSD center is same ? Measure BG by DSSD itself

Very Rough Estimation of Dose We can measure dose using its energy deposition - Occupancy ~ 10 % - Energy Deposition ~ 46 keV/ch - Bunch cycle 10 usec - Shaping time 2.6~3.0 usec  ~100 kRad/yr - No subtraction of electrical noise, bad-ch effect - Contribution below threshold (~15keV) is not considered - Need to consider below th. for SR (low energy should be dominated by SR) Must measure for each components

SVD Hit Occupancy (hit-rate) 1 st layer (R=2 cm) 10~12 % (HER 1.1A, LER 1.6A) Before (R=2.5 cm) 7 ~ 8 % (HER 1.0A, LER 1.5A) 2 nd layer (4.3 cm) ~ 4 %, 3 rd, 4 th layer ~ 2 %

SVD Occupancy (hit-rate) SVD 1.6SVD 2.0 beampipe radius Large diff. of occ. btw 1 st – 2 nd layers may come from 1/(r-r bp ) relation

Single Bunch like Run HER 15 mA, with adjusting trigger timing SVD 1 st layer occupancy ~ 0.2 %  corresponds to ~ 4 % 1.1 A Energy deposition 15.2 keV/ch  corresponds to ~20 kRad/yr 1.1 A (33 kRad/yr at maximum position,  =180deg) ( contribution below th. is corrected by simulation) SVD 2.0 SVD 1.X data simulation

Correlation with Vacuum Average Pressure (N particle /N SR ) / P(Pa) = const Upstream Pressure

Background at Collision 71 kRad/yr 11 kRad/yr Total dose Particle-BG SR-BG Run1560 (threshold ~15 keV) HER : 1.1 A, LER : 1.6 A Consistent with expectation from single-beams

Study of Touschek (life-time) 1.4A 1.1A Touschek contribution < 20 % at collision ~ 45 % at single beam 42 % in simulation Smaller beam-size (density)  shorter life-time and larger background If no Touschek Single beam run Touschek contribution must be corrected 1/   beam-density Collision run

Layer dependence (collision run) Particle-BGSR-BG BG  1/(r-r bp ) BG comes from beampipe radius ? Large difference of occupancy btw 1 st and 2 nd layer

Is there reasonable reason to explain 1/(r-r bp ) correlation? Be pipe SR is scattered / absorbed at Au coating Backscattered Hard-SR e- Spent particles are scattered thin-Ta region Large contribution comes from here (simulation) Ta Be pipe