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The Belle II Silicon Vertex Detector assembly and mechanics
Stefano Bettarini Universita’ di Pisa & INFN On behalf of the Belle II SVD Group Feb 16th, 2016 VCI-2016
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OUTLINE Belle II at SuperKEKB The Belle II SVD The “Origami Concept”
Overview of ladder assembly Results from recent test-beams Schedule & Conclusions Feb 16th, 2016 VCI-2016
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The Belle II Experiment @ SuperKEKB
e- 7GeV 2.6 A e+ 4GeV 3.6 A Belle II is an e⁺-e⁻ collider experiment √s̄ ≈ mΥ(4S) target luminosity: L = 8.0 x 10³⁵/cm²s Int. luminosity [ab-1] Peak luminosity [cm-2s-1] New physics search beyond the SM in Belle II The CP-violating parameters in various B-decay modes will isolate a New Physics model out of the several hypotheses. Precise determination of the vertices and low-momentum track measurements are essential to perform the studies on rare or suppressed B and D decays Feb 16th, 2016 VCI-2016
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Belle II Vertex Detector
Talk on PXD by F. J. LUTTICKE PiXel Detector (PXD) The innermost detector composed of two layers of DEPFET pixels. Silicon Vertex Detector (SVD) Next inner detector to the PXD composed of 4 layers of double-sided silicon strip detectors. For a better vertex resolution and KS⁰ reconstruction efficiency, the outer SVD radius is doubled wrt the Belle SVD. Forward SVD Track impact parameter resolution: σd₀ [mm] σd₀ ~ 40μm @ pT = 2GeV/c PXD Angular acceptance 17⁰<θ<150⁰ Feb 16th, 2016 VCI-2016 pT [GeV/c]
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The SVD ladder design ~650 mm Kavli-IPMU HEPHY TIFR Melbourne Pisa
Layer # of ladders Radius (mm) L6 16 140 L5 12 115 L4 10 80 L3 7 39 L6 Ladder L5 Ladder L4 Ladder L3 Ladder FWD module BWD module Origami +z Origami ce Origami -z BWD FWD Cooling pipe Kavli-IPMU HEPHY TIFR Melbourne Pisa Feb 16th, 2016 for L4L6 VCI-2016
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SVD Sensors Readout ASIC
Poster Session B – Board: 55 by M.VALENTAN (MPI) Sensor thickness μm N⁺ strip Si Double-sided Si strip detector P⁺ strip Readout ASIC (APV25) To cope with the Belle II high hit rate the readout chip should have a short signal shaping time for low noise and a good radiation hardness. Rectangular Trapezoidal # of p-strips 768 p-strip pitch[μm] 75 (L3:50) 5075 # of n-strips 512 (L3:768) 512 n-strip pitch[μm] 240 (L3:160) 240 Active area[mm²] 7030 (L3:4738) 5890 We adopted the APV25 The APV25 was originally developed for the CMS. Shaping time = 50ns. Radiation hardness > 1MGy. Other characteristics # of input channels = 128 / chip. 192-deep analog pipeline for the dead-time reduction. Thinned to 100μm for material budget reduction. Micron HPK Feb 16th, 2016 VCI-2016
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Chip-on-Sensor and “Origami” Concept
APV25 on the sensor An APV25, reading out a sensor, is placed on the sensor to minimize the analog path length for the capacitive noise reduction. Sensor backside readout Signals on the sensor backside are transferred to the sensor front side by other flex circuits and readout by APV25 chips mounted on the front side. Readout ASICs on the same side & same line → easier chilling by a single cooling pipe. Feb 16th, 2016 VCI-2016
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Snapshot of the “Origami” Concept
DSSD backside Flex APV25 DSSD The backside (phi-side) signals are transmitted to the APV25 via wrapped Flex Circuits, glued above the m-bondings of the Z-side DSSD front side with APV25s Flex glued before bonding Feb 16th, 2016 VCI-2016
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Challenges of ladder assembly
In the layer3 ladder sensors are placed head to head, conventionally read-out outside the sensitive region. The other layers (L4L6) have a lantern shape, with the slanted subassembly on the forward, a backward subassembly and different numbers of origami subassemblies in the middle: L4 one Backward Origami (O-z) L5 “ one central (Oce) L6 “ “ one forward (O+z) All the components have to be properly aligned and positioned (i.e. glued) on the support structure (C.F. ribs), matching tight geometrical tolerances. The jigs and chucks used during the assembly phases have been checked to have precision falling within the design limits. Feb 16th, 2016 VCI-2016
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Example: FW/BW Subassembly gluing jig
Materials: Aluminum EN AW 5083 All surfaces touching DSSDs are made of Teflon and vacuum circuit implemented Overall mech. tolerances O(30 um) Feb 16th, 2016 VCI-2016
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One more example: L5 BWD & Slant Jigs
Blocks (BWD) and wedges (FWD): Milled together in one step Mechanism to grab and position hybrid board Angle between the surface of assembly base and slanted sensor: Design value: 16.00° Measured value: 15.97° (between base and wedge block surface) Measured values: 15.93° ° between base and Delrin® surface of slant jig (repeated several times by removing and re-placing slant jig) Error on angle < 0.1° ! Feb 16th, 2016 VCI-2016
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Ladder anatomy Components: L6 ladder Origami hybrid APV25 PA0 PF2 PF1
DSSD x2 small rectangular (L3) x2-4 large rectangular (L4-6) x1 trapezoidal (L4-6) Origami hybrid APV25 Origami hybrid Flexible circuit to transmit detector signals to the ladder ends. APV25 Readout ASIC of the strips. PA0 PF2 FlexPA (PA/PF/PB) Flexible circuit to transmit detector signals to the APV25. PF1 AIREX PB2 PA1 PA2 DSSD PA0 Flexible circuit glued on the Origami hybrid to transmit n-side detector signals to the APV25. L6 ladder PB1 AIREX Thermal insulator between the DSSD and APV25. Rib Feb 16th, 2016 VCI-2016
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Overview of L4L6 ladder assembly
Complex procedures, up to 25 vacuum jigs required! BW and FW subassemblies produced in Pisa, then shipped to the assembly sites: L4 L5 HEPHY (Vienna) L6 IPMU (Tokyo) FW BW All sites have assembled SVD modules with electrical functionality and are getting ready for (or are already in) mass production. Feb 16th, 2016 VCI-2016
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Assembly process flow The ladder assembly procedure can be divided into main steps: The production of FW/BW The production (on each site) of the Sensor+PA subassemblies and assembly of the mechanical structure (C.F. ribs) Sensors and subassembly alignment on the assembly bench Construction of the origami subassemblies The ladder assembly, by gluing all the subassemblies on the ribs Mechanical survey Final test with b-source Many intermediate optical checks and several electrical tests performed during assembly. Approximately 3 weeks of assembly time! As an example, the procedures of a L5 ladder will be described Feb 16th, 2016 VCI-2016
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1. FW/BW subassembly Flex phi-side gluing: Microbonding Shipping
alignment of the detector and hybrid boards on the gluing jig Alignment, gluing of the phi-PA Microbonding Shipping (survey) Z-side gluing: Electrical test and laser scan Feb 16th, 2016 VCI-2016
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2.a Sensor+PA subassembly
Applying glue onto pitch adapter DSSD pre-alignment Wire bonding 2.b Rib-assembly Feb 16th, 2016 VCI-2016
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3. Sensors and subassembly alignment on the assembly bench
Positioning DSSDs onto assembly bench Alignment of DSSDs and BW/FW subassembly by an xyz-q stage Feb 16th, 2016 VCI-2016
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4. Origami subassembly PA wrapping: Layer 6 has also the O+z
After airex gluing, OCE already glued onto sensor (only L5,L6), applying glue onto O-Z Glue applied to PA, vacuum micro manipulators used to bend and glue pitch adapters Attaching O-Z (all L4,L5,L6) Uniform glue spread required for wirebonding Origami flexes glued onto sensors, n-side bonded Layer 6 has also the O+z Feb 16th, 2016 VCI-2016
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5. The ladder assembly Layer6 ladder has one more origami (O+z)
FW subassembly gluing BW subassembly gluing Half-ladder and Origami sub-assembly before final steps Applying glue onto BW sensor and ribs Attaching the origami assembly to the ribs by lowering the vertical stages Layer6 ladder has one more origami (O+z) Feb 16th, 2016 VCI-2016
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6. Mechanical survey under CMM
F-marks at DSSD corners used for part alignment during assembly and final measurement on the ladder. Ladder coordinate frame Feb 16th, 2016 VCI-2016
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6. Survey results h g e f delta x [µm] x [mm] delta y [µm] Displacement wrt nominal position (for L5.904, average of 4 meas.): better than ±100µm in all directions delta z [µm] Feb 16th, 2016 VCI-2016
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7. b-source test Electrical tests of L5.903 in lab. with a 90Sr source (12 MBq) Test setup: the ladder is mounted on a moveable stage of a dark box scintillator Space for 90Sr source All noise patterns look as expected: p-side: 2.5 ADC / n-side: 2.1 ADC SNR in the expected range: p-side =15 / n-side =18 (for cluster width=2) Operating the full ladder simultaneously works as good as individual parts Shades by the support ribs are clearly observed in the hit maps Feb 16th, 2016 VCI-2016
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The Belle II SVD Data Readout System
Poster session A – Board: 82 by R. Thalmeier (AT) The Belle II SVD Data Readout System “COPPER” board RX x48 FADC Data stream CPU SVD FADC Zero supp. Formatter Repeater to HLT ~2m ~10m belle2link TX x1748 APV25s Aurora link TRG/CLK signals PXD region of interest gen VME to PXD x4 buffer Data size reduction FADC Ctrl APV trig gen Decoder Cu cable Trigger/ timing distributor Central TRG FADC-Ctrl SVD readout system Central DAQ Prototypes of all components have been developed. Feb 16th, 2016 VCI-2016
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Recent Tests on Beam 1. DESY (e- 26 GeV) Jan. 2014:PXD + SVD
SVD fast-tracking provides ROI (Region-Of-Interest) selection in PXD to keep the data readout bandwidth under control 2. CERN-SPS (120 GeV) June 2015: SVD a. DUT = final ladder (final components) L5.903 into the test-box and 3 single sensor’s telescope b. DUT = BW and FW subassemblies EUDET as reference telescope beam Feb 16th, 2016 VCI-2016
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Analysis Results from Desy Beam Test
SVD tracks reconstructed in real time on the High Level Trigger and then the PXD sensor is read out based on the ROI information. observed performance of SVD module cluster size distribution cluster charge distribution peak: corresponds to about 22,000 𝑒 event displays SVD modules reconstructed track 1 T magnetic field position of track projection [cm] cluster hit efficiency for tracks efficiency: 99.4% efficiency cluster hit efficiency for tracks From the resulting high efficiency, we confirmed that our Common Mode Correction and zero-suppression do not lose SVD hit efficiency. Feb 16th, 2016 VCI-2016
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CERN Beam Test: SNR on L5.903 Mean single strip noise:
p-side BW n-side p-side FW n-side p-side Z n-side p-side CE n-side all all 1 2 3+ Cluster Width Mean single strip noise: 2.7 ADC on p-side 2.5 ADC on n-side (SNR with cluster noise) clw=2 w/o cooling CO2 cooling -20°C n-side 14 15 p-side 12 12,5 Full FADC readout system: no interference within modules Cooling slightly improves the SNR Feb 16th, 2016 VCI-2016
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Resolution on BW/FW subassembly (CERN Test Beam )
Digital resolution (intermediate floating strip) Feb 16th, 2016 VCI-2016
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Radiation monitoring & Beam Abort
6 + 6 sensors Close to SVD L3 support rings 4 + 4 sensors PXD-beam pipe Single Crystal Diamonds, scCVD 4.5x4.5x0.5 mm3 Long high quality cabling and current measurement Small sensors and compact mechanics 12 x 20 x 3.1 mm3 multi-layer package Shielded diamond sensors Voltage sources (150÷500 V) picoAmmeters Feb 16th, 2016 VCI-2016
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Global Schedule High level milestones Date Mass production ladder
STARTED 2nd beam test (PXD+SVD combined) Apr. 2016 Start of Ladder mount to support structure Feb SVD readiness in KEK Dec. 2017 Start of PXD+SVD integration Start of VXD installation into Belle II Jun. 2018 Start of physics run 4Q 2018 Feb 16th, 2016 VCI-2016
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Conclusions Precision B-decay vertex detection is a crucial issue to access to physics beyond the SM at Belle II. For this, a highly hermetic vertex detector has been designed. First electrically full functioning ladders have been completed, demonstrating well established ladder assembly procedure. Mechanical precision proven by the prototype ladders Good electrical performance confirmed with both source measurements and beam tests (Final prototype) DAQ system is confirmed working in the beam test Ladder mass production has started. Belle II physics run will start in 4Q 2018. Feb 16th, 2016 VCI-2016
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Backup slides Feb 16th, 2016 VCI-2016
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Kokeshi pin = origin of ladder
Mounting a Ladder End mount Ladders are positioned by two precision pins Fixed on backward side (origin) Sliding on forward side to allow thermal movement (verified effective with thermal cycles) BWD Kokeshi pin = origin of ladder FWD Swallow tail Feb 16th, 2016 VCI-2016
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Cooling pipe attachment
Cradle rod Cooling pipe attachment Cradle rail with pusher tool Cradle Support Two Arm Support Ladder Mount micro-positioner tower Cooling-tube-set Axis of rotation Pipe clamp Feb 16th, 2016 VCI-2016
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Vibrational test (on an L5 ladder)
Heavy Al support structure (resonance at 920 Hz) shaker Frequency sweep from 20 to 1000 Hz (0.2 g) show no resonances below 100 Hz Feb 16th, 2016 VCI-2016
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