Nov. 7, 2005Vertex2005 A. Kibayashi 1 Status of the BELLE Silicon Vertex Detector Vertex2005 Nikko Nov. 7-11, 2005 Atsuko Kibayashi Tokyo Institute of Technology on behalf of the Belle SVD Group - Belle Detector at KEKB - History of SVD at Belle - Trigger Updates - Performance - Future Prospects - Recent Problems - Summary

Nov. 7, 2005Vertex2005 A. Kibayashi 2 KEKB Asymmetric e + (3.5GeV) e - (8GeV) Collider L peak = x /cm 2 /s (May 2005) ∫Ldt = /fb (Oct 20,2005) KEKB Collider Belle Detector 3km World Record ! Tsukuba, Japan

Nov. 7, 2005Vertex2005 A. Kibayashi 3 B 0 or B 0 (flavor tag side) 8GeV electron 3.5GeV positron  s) CP eigenstate  z ~ 200  m Physics Motivation Measurement of time dependent CP violation B mesons: c  = 460  m boost:  = 0.42 decay distance~ 200  m  Requires vertex resolution ~ 100  m

Nov. 7, 2005Vertex2005 A. Kibayashi 4 Silicon Vertex Detector Central Drift Chamber Aerogel Cherenkov Counter Time Of Flight Counter CsI Electromagnetic Calorimeter Superconducting Solenoid coil K L muon detector 8GeV electron beam 3.5GeV positron beam The Belle Detector

Nov. 7, 2005Vertex2005 A. Kibayashi 5 SVD History SVD1.0VA chips with 1.2  m process (usable up to 200kRad) read-out chips damaged by soft X-rays SVD1.2 a gold foil wrapped on the beam pipe to stop the X-rays SVD1.4 VA chips with 0.8  m (function up to 1Mrad) vacuum leak on the beam pipe SVD1.6 ladders damaged by radiation replaced

Nov. 7, 2005Vertex2005 A. Kibayashi 6 SVD1 vs. SVD2 No. of Layers : 3  4 low momentum tracking Beam Pipe : 20 mm  15 mm better vertex resolution Full CDC Coverage Front-end electronics moved out of acceptance Outer most layer further away from the interaction point more decays inside SVD region

Nov. 7, 2005Vertex2005 A. Kibayashi 7 SVD1 vs. SVD2 : performance Large improvement at lower momentum region! SVD1SVD2 No. of layers34 R of 1st. layer32 cm pitch size z84 75  m r   m Large improvement overall! rr z Impact Parameter Resolutions

Nov. 7, 2005Vertex2005 A. Kibayashi 8 SVD2 3.5 GeV e + 8 GeV e - Collaboration U. Hawaii, JAXA, Jozef Stefan Inst., Kanagawa U, KEK, Krakow INP, LBNL, U. Melbourne, National Taiwan U., Nihon Dental College, Niigata U., Nova Gorica Polytech., Osaka U., Princeton U., U. Sydney, Tohoku U., U. Tokyo, Tokyo Inst. Tech., U. Tsukuba, Toyama NCMT, Vienna IHEP over 20 institutions ~100 people VA1TA read-out chip

Nov. 7, 2005Vertex2005 A. Kibayashi 9 VA1TA chip SVD2 Front-end Readout VA1  Analog readout shaping time 0.3~1.0  s 128 channel serial read-out with 5MHz clock TA  SVD L1 Trigger faster shaper (75ns or 300ns) + discriminator 128 wired-or out put L0 trigger: tell VA to hold L1 trigger: get the held signal FADC start AD conversion

Nov. 7, 2005Vertex2005 A. Kibayashi 10 SVD2 : Radiation Hardness VA1TA 0.35  m radiation hard upto ~20 Mrad average accumulated dose in first layer ~240 krad maximum accumulated dose in first layer ~530 krad  Gain stable

Nov. 7, 2005Vertex2005 A. Kibayashi 11 SVD2: Signal to Noise Ratio Degradation 1st & 2nd Layer ~20 % 3rd & 4th Layer ~stable

Nov. 7, 2005Vertex2005 A. Kibayashi 12 L0 Trigger Upgrade : Motivation Luminosity15/nb/s45+/nb/s Backgroundx1x3+ L0 trigger rate5kHz45kHz SVD Hold Efficiency 96%86% Exp41 HadronC  Need to reduce L0 rate, while keeping high efficiency.

Nov. 7, 2005Vertex2005 A. Kibayashi 13 L0 Trigger Update: what's done new hardware installed added CDC layers (CDC trigger upgrade in summer) CDC + small cell CDC + TOF  Hold efficiency ~95%  L0 rate reduced to 1/4 Fast TOF trigger + small cell CDC - SVD TA too slow Hold efficiency ~ 96% L0 trigger rate ~5kHz Before Summer 2005 Summer 2005 L0 rate can be reduced by coincidence with more layers.

Nov. 7, 2005Vertex2005 A. Kibayashi 14 Trigger Updates : SVD Z trigger Many off-IP background events cause fake triggers. –Z trigger would be a solution. SVD provides the best Z resolution SVD2 Z triggers –L1T trigger fast signal from VA1TA –L1.5 trigger digitized strip data from FADC hardware installed in Summer 2003

Nov. 7, 2005Vertex2005 A. Kibayashi 15 L1T Z trigger updates GDL rate reduced by ~10% Detection eff.: ~ 99% (hadron) ~ 61% (mupair) Idea - Utilize fast peaking time of TA - Combine with CDC r-  trigger for better BG reduction Problem - Efficiency too low Idea - Reduce dead time- work with predefined masks Problem - Only 2~3 % improvement BB-pair Hz Current85.1%78.5% w/ L %79.8% SVDL1TRateRejection off476 Hz1.00 on424 Hz0.89 include L1T in GDL probability of not losing any BB-pairs  Terminate L1.5

Nov. 7, 2005Vertex2005 A. Kibayashi 16 installment plan early 2006 Crab Crossing: a new idea for higher luminosity Head-on collisions with finite crossing angle (22mrad)! - avoid parasitic collisions - collisions with highest symmetry  large beam-beam parameter (  0.19) Future Prospects Luminosity will be more than doubled!!  Study the effect of x3 luminosity x3 backgrounds

Nov. 7, 2005Vertex2005 A. Kibayashi 17 SVD2 Occupancy Current Occupancy 1st layer : 9 ~10 % 2nd layer 3~4% 3rd & 4th layers 1~2% At high luminosity ~ high background ~ high occupancy (occupancy = % of hit channels)  Study performance under high (~30%) occupancy.

Nov. 7, 2005Vertex2005 A. Kibayashi 18 Intrinsic Resolution vs. Occupancy Intrinsic Resolution  Occupancy residual occupancy < 0.04 occupancy  0.3 At high occupancy,  cluster shape is 'distorted'  reconstructed cluster energy to be off  the residual distribution to be widened

Nov. 7, 2005Vertex2005 A. Kibayashi 19 Hit Efficiency vs. Occupancy Layer1 Layer2 Layer3 Layer4 hit or not? Layer No. 0%  30% Occupancy 1.0  0.6 Efficiency Higher Occupancy ~ Lower Hit Efficiency Signal + background hits  wider 'distorted' cluster Wrongly associated background cluster

Nov. 7, 2005Vertex2005 A. Kibayashi 20 Vertex Resolutions vs. Occupancy 3xBG MC Impact Parameter Resolution  Occupancy Z Resolution Degradation Impact parameter resolutions for higher momentum tracks ~10% Z resolution for lower momentum clusters ~17% J/  Ks Use correlations between - cluster detected charge from both sides of a DSSD (wrongly associated clusters) - cluster size and track incident angle ( BG induced hits)  Software efforts in progress.

Nov. 7, 2005Vertex2005 A. Kibayashi 21 Recent Problems: How we saw Oct. 5 After HER beam abort, at the beginning of the next run, noise monitor showed some chips have gone null.. Oct. 17 After an earthquake (M5.1), some more hybrids seemed to have gone dead, but later recovered.

Nov. 7, 2005Vertex2005 A. Kibayashi 22 Recent Problems: Initial investigation LV monitor shows 0 current. LV supplied to the repeater system inside of the endcap. Checked power supply cables, relay cable connector pins  No problems Checked resistance in each power cable. Some are found to be very large.  Open endcap

Nov. 7, 2005Vertex2005 A. Kibayashi 23 Recent Problems: Where it happened? In the front-end repeater system. - receives the analog signals from the VA1TA chips, amplifies them, and sends to the backend electronics (FADCs). - accepts control signals from the backend timing modules, converts and sends to VA1TA chips. - provides detector bias voltages located just outside of the CDC end wall 5 forward, 5 backward

Nov. 7, 2005Vertex2005 A. Kibayashi 24 Recent Problems: Power connector Connector pins can handle ~3A according to the spec. Our operation <3A. Pins made of phosphorus bronze, tin-plated. Housing made of nylon.

Nov. 7, 2005Vertex2005 A. Kibayashi 25 Recent Problems: Burnt connectors FW1 Power supply connectors. forward 2/5 badly burnt, 1 1pin backward 1/5 slightly FW4 Cause still under investigation!

Nov. 7, 2005Vertex2005 A. Kibayashi 26 Recent Problems: A quick fix FW x5: Avoid using the connector. Solder wire directly. BW x5: Polished pins. Confirmed R not high. Installed temperature monitor. Keep monitoring temp. & R.  Resume KEKB/Belle operation 10/20 ~8am stopped normal run, opened endcap 11/1 endcap closed, 11/4 start taking data

Nov. 7, 2005Vertex2005 A. Kibayashi 27 Summary SVD2 Operation –No serious problems for 2 years –Performance within expectations Trigger Updates –L0 trigger updated to cope with higher background –L1T, L1.5 trigger activities have been terminated Next Year : Expect x3 Higher Luminosity –L0 trigger upgraded –Software works in progress Problem in Oct. –A quick fix finished –Cause still under investigation

Nov. 7, 2005Vertex2005 A. Kibayashi 28 backups

Nov. 7, 2005Vertex2005 A. Kibayashi 29 Alignment Alignment Move each DSSD so that the track is a straight line matching the position of the signal hit on the DSSD. –Shift : x, y, z –Rotation : x, y, z –246 DSSDs 1,476 parameters total y x z Double-Sided Silicon Detector (DSSD) Track signal Use cosmic ray tracks with the mag. field off.

Nov. 7, 2005Vertex2005 A. Kibayashi 30 SVD2 Performance dr  < 20  m, dz < 30  m IP resolution stable at ~10% fluctuation a b Summer03  Summer04  Summer05 

Nov. 7, 2005Vertex2005 A. Kibayashi 31 Signal and Noise Cluster EnergyNoise

Nov. 7, 2005Vertex2005 A. Kibayashi 32 Leak Current

Nov. 7, 2005Vertex2005 A. Kibayashi 33 SVD1 vs. SVD2