1. 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

2. 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

3. 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

4. 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]

5. 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 L4L6
VCI-2016

6. 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)
5075
# 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

7. 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

8. 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

9. Challenges of ladder assembly
In the layer3 ladder sensors are placed head to head, conventionally read-out outside the sensitive region.
The other layers (L4L6) 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

10. 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

11. 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

12. 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

13. Overview of L4L6 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

14. 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

15. 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

16. 2.a Sensor+PA subassembly
Applying glue onto pitch adapter
DSSD pre-alignment
Wire bonding
2.b Rib-assembly
Feb 16th, 2016
VCI-2016

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. Recent Tests on Beam 1. DESY (e- 26 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

25. 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

26. 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

27. Resolution on BW/FW subassembly (CERN Test Beam )
Digital resolution
(intermediate floating strip)
Feb 16th, 2016
VCI-2016

28. 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

29. 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

30. 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

31. Backup slides
Feb 16th, 2016
VCI-2016

32. 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

33. 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

34. 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