1. A SiW EM Calorimeter for the Silicon Detector
Santa Fe, NM
June 8, 2012
Norman Graf
(for the SiW ECal group)

2. Overview Motivation (LC physics) and goals Applications: ILC (SiD)
A Higgs factory LC ? CLIC ?
Muon Collider ?
Other ?
Project R&D status
Sensors
KPiX readout
Interconnects
Integrated !
Plans

3. SiW R&D Team KPiX readout chip detector development interconnects
M. Breidenbach, D. Freytag, N. Graf, R. Herbst, G. Haller, J. Jaros, T. Nelson
SLAC National Accelerator Laboratory
J. Brau, R. Frey, D. Strom,
Craig Gallagher (tech),
D. Meade, P. Radloff (grad students),
(undergrads)
U. Oregon
B. Holbrook, R. Lander, M. Tripathi,
M. Woods (grad student)
UC Davis
KPiX readout chip
downstream readout
mechanical design and integration
detector development
readout electronics
testing and integration
interconnects

4. “Imaging Ecal”: Motivated by LC Physics
Guiding principles: Measure all final states and measure with precision
Multi-jet final states (t-chan, missing E, combinatorics)
 measurement should not limit jet resolution
id and measure h and h± showers
track charged particles
Tau id and analysis
Unique window on BSM
Photons
Energy resolution, e.g. h
Vertexing of photons ( b1 cm ), e.g. for GMSB
Electron ID
Bhabhas and Bhabha acollinearity
Hermiticity
 Imaging (E)Calorimetry can do all this (“particle flow”)

5. ILC Application Drives Design
ILC bunch train structure
Power pulsing  passive cooling using the tungsten (average heat load is <1% of max)
Readout cadence
Beam energy
Electronics dynamic range and noise: single MIPs (tracking) to 500 GeV EM showers (up to 2000 MIPs/pixel).
Physics
pixel area (particle flow -- jets, taus)
longitudinal structure (energy resolution)

6. R&D Goals Design a practical ECal which
meets (or exceeds) the LC physics requirements
with a technology that would actually work at a LC…
Physics  A highly-segmented imaging Si-W ECal
Very collimated EM showers and MIP tracking;
Modest EM energy resolution OK
Key to making this practical is a highly integrated electronic readout
~1000 pixels per readout chip (KPiX) with power pulsing
Readily segmented silicon: 13 mm2 is current default
Interconnects give small readout gap (1 mm): 13 mm eff. Moliere radius
Bump-bond KPiX directly to Si sensor
Flex cables to outside

7. Segmentation Requirement
Resolve individual photons from jets, tau decays, …
Resolving power depends on shower radius and segmentation.
Want transverse segmentation significantly smaller than RMoliere = ~10 mm
Dense absorber, thin readout, lateral segmentation
Two EM-shower separability
in LEP data with the OPAL
Si-W LumCal (David Strom)

8. Silicon Sensor Transverse Segmentation
Silicon is easily segmented
KPiX readout chip is designed for 13 mm2 pixels (1024 pixels for 6 inch wafer)
Cost nearly independent of seg.
Limit on segmentation comes from chip power (minimum  2 mm2 )
KPiX ASIC and sample trace
Fully functional prototype (Hamamatsu)

9. Silicon Sensor Longitudinal Segmentation
Critical parameter for RM is the gap between layers

10. ECal schematic cross section
Metallization on detector from KPix to cable
Bump Bonds
Tungsten
Gap ~1 mm
Kapton Data Cable
KPix
Si Detector
Kapton
Tungsten
Heat Flow
Thermal conduction adhesive

11. KPiX Circuit Schematic
Storage until end of train.
Pipeline depth presently is 4
13 bit A/D
Si pixel
Dynamic gain select
Leakage current subtraction
Event trigger
calibration

12. Bump-bonding
X-ray of Kpix bumps to sensor

13. Flex-cable Attachment

14. SiD Ecal Sensors KPiX bump-bonded to sensor
Cable bump-bonded to sensor
Assembly 1mm high
Contract IZM to bump-bond sensors
Sufficient for full longitudinal testbeam stack

15. Cross-Talk Study Red: Pulse 4 random pixels with 500 fC,
Blue: No pixels pulsed.
Plot residuals for all pixels.
<1 fC level for a total injected charge of 2 pC. Crosstalk in this test is thus <0.1%.

16. Cosmic Ray Bench Tests
First silicon sensor with bump-bonded KPiX chip
(Red) cosmic-ray triggered: hit pixel + noise
(Blue) sensor removed: noise only
Signal distribution as expected for MIPs (~4 fC)
Good separation from noise
No measurable crosstalk to non-hit channels
Low leakage current (as expected)
Will do battery of tests with MIPs, sources, IR laser

17. Cosmic Ray Self-trigger Test

18. Longitudinal Sampling
Compare two tungsten configurations:
30 layers x 5/7 X0
(20 x 5/7 X0) + (10 x 10/7 X0)
Resolution is 17% / √E , nearly the same for low energy (photons in jets)
Better for the config. at the highest energies (leakage)  adopt as baseline

19. Testbeam Assembly

20. SiD Baseline Configuration
Transverse segmentation
13 mm2 pixels
Longitudinal:
(20 x 5/7 X0) +
(10 x 10/7 X0)  17% / E
 1 mm readout gaps
 13mm effective Moliere radius
~3.5x3.5 mm2
Cooling (~20mW/KPiX)
hex
Digital signals & power

21. ECal schematic readout
Data Concentrator
“Longitudinal” Data Cable
“Transverse” Data Cable
Readout Chip “KPix”
Detectors
Locating Pins
Tungsten Radiator
~ 1m

22. ECal Cooling Electronics operated in pulsed mode  20mW per chip
Active cooling required (each sub detector must remove the heat produced)
Cold plate with water pipes routed laterally of the wedge
Total heat load per wedge module 115 Watt
Max DT ~ 1.35oC
8 x 20mW
R1= DT/Q=1.35/0.16 =8.43oC/W
Max DT ~ 1.35oC

23. Timeline for R&D
Complete contract & bump-bond KpiX chips and cables to Hamamatsu sensors.
Assemble test module
Secondary End Station test beam at SLAC, which is now scheduled to be ready for use in late 2012
Construct full scale prototype, full width & thickness, short z length
Stainless steel in place of Tungsten
Perfect Test bed for
the small screws design
The integration of the electrical interconnections
the cooling cold plates

24. Summary
A narrow gap silicon-tungsten detector is an attractive solution for a highly-segmented (transverse and longitudinal), compact (rMoliere, X0) detector for ILC physics requiring individual particle reconstruction.
A highly integrated electronic readout can provide a practical realization of such an ECal.
The development of such a readout chip is well underway.
Prototypes of sensors, chips and cables are in hand, beam tests of full stack awaited.
Physics studies to characterize and optimize the performance of the ECal as part of the combined SiD concept continue.