1. A MAPS-based readout of an electromagnetic calorimeter for the ILC
Nigel Watson
(Birmingham Univ.)
Motivation
Physics simulations
Sensor simulations
Testing
Summary
For the CALICE MAPS group
J.P.Crooks, M.M.Stanitzki, K.D.Stefanov, R.Turchetta, M.Tyndel, E.G.Villani
(STFC-RAL)
Y.Mikami, O.D.Miller, V.Rajovic, NKW, J.A.Wilson (Birmingham)
J.A.Ballin, P.D.Dauncey, A.-M.Magnan, M.Noy (Imperial)

2. ILC: high performance calorimetry
Essential to reconstruct jet-jet invariant masses in hadronic final states, e.g. separation of W+W, Z0Z0, tth, Zhh, H
Mass (jet1+jet2)
Mass (jet3+jet4)
E/E = 60%/E
E/E = 30%/E
Equivalent best LEP detector
Goal at ILC
LEP/SLD: optimal jet reconstruction by energy flow
Explicit association of tracks/clusters
Replace poor calorimeter measurements with tracker measurements – no “double counting”
Little benefit from beam energy constraint, cf. LEP
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

3. ECAL design principles
Shower containment in ECAL,  X0 large
Small Rmoliere and X0 – compact and narrow showers
int/X0 large,  EM showers early, hadronic showers late
ECAL, HCAL inside coil
Lateral separation of neutral/charged particles/’particle flow’
Strong B field to suppresses large beam-related background in detector
Compact ECAL (cost of coil)
Tungsten passive absorber
Silicon pixel readout, minimal interlayer gaps, stability
“Swap-in” alternative to Si diode detector designs, e.g. in LDC, SiD
CMOS process, more mainstream:
Industry standard, multiple vendors (schedule, cost)
(At least) as performant – ongoing studies
Simpler assembly
Power consumption larger – but better thermal properties
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

4. Weighted no. pixels/event Incoming photon energy (GeV)
Basic concept for MAPS
Swap ~0.5x0.5 cm2 Si pads with small pixels
“Small” := at most one particle/pixel
1-bit ADC/pixel, i.e.
Digital ECAL
Effect of pixel size
How small?
EM shower core density at 500GeV is ~100/mm2
Pixels must be<100100mm2
Our baseline is 5050mm2
Gives ~1012 pixels for ECAL – “Tera-pixel APS”
Weighted no. pixels/event
50mm
>1 particle/
pixel
100mm
Incoming photon energy (GeV)
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

5. Tracking calorimeter
5050 μm2
MAPS pixels
ZOOM
SiD 16mm2 area cells

6. Geant4 energy of simulated hits
Physics simulation
0.5 GeV
MPV = 3.4 keV
σ = 0.8 keV
5 GeV
200 GeV
Geant4 energy of simulated hits
Ehit (keV)
MAPS geometry implemented in Geant4 detector model (Mokka) for LDC detector concept
Peak of MIP Landau stable with energy
Definition of energy: E a Npixels
Artefact of MIPS crossing boundaries
Correct by clustering algorithm
Optimal threshold (and uniformity/stability) important for binary readout
20 GeV photons
s(E)/E
Threshold (keV)
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

7. Architecture-specific
CALICE INMAPS ASIC1
0.18mm feature size
First round, four architectures/chip (common comparator+readout logic)
INMAPS process: deep p-well implant 1 μm thick under electronics n-well, improves charge collection
4 diodes
Ø 1.8 mm
Architecture-specific
analogue circuitry
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

8. Device level simulation
Physics data rate low – noise dominates
Optimised diode for
Signal over noise ratio
Worst case scenario charge collection
Collection time
Signal/noise
0.9 μm
1.8 μm
3.6 μm
Distance to diode
(charge injection point)
Signal/Noise
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

9. Near future plans 3 July: 1st sensors delivered to RAL
Work ongoing on the set of PCBs holding, controlling and reading the sensor.
Test device-level simulations using laser-based charge diffusion measurements at RAL
l=1064, 532,355 nm,focusing < 2 μm, pulse 4ns, 50 Hz repetition, fully automated
Cosmics and source setup, Birmingham and Imperial, respectively.
Potential for beam test at DESY end of 2007
Expand work on physics simulations
Test performance of MAPS ECAL in GLDC and SiD detector concepts
Emphasis on re-optimisation of particle flow algorithms
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

10. Summary Concept of CMOS MAPS digital ECAL for ILC
Multi-vendors, cost/performance gains
New INMAPS deep p-well process (optimise charge collection)
Four architectures for sensor on first chips, delivered to RAL Jul 2007
Tests of sensor performance, charge diffusion to start in August
Physics benchmark studies with MAPS ECAL to evaluate performance relative to standard analogue Si-W designs, for both SiD and LDC detector concepts
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

11. Backup slides…
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

12. Type dependant area: capacitors, and big resistor or monostable
Architectures on ASIC1
Presampler
Preshaper
Type dependant area: capacitors, and big resistor or monostable
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

13. Beam background studies
purple = innermost endcap radius
500 ns reset time  ~ 2‰ inactive pixels
Beam-Beam interaction by GuineaPig
Detector: LDC01sc
2 scenarios studied :
500 GeV baseline,
1 TeV high luminosity
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

14. The sensor test setup 1*1 cm² in total 5 dead pixels
2 capacitor arrangements
2 architectures
6 million transistors, pixels
5 dead pixels
for logic :
hits buffering (SRAM)
time stamp = BX
(13 bits)
only part with clock lines.
7 * 6 bits pattern
per row
84 pixels
42 pixels
Row index
Data format
= 31 bits per hit
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

15. Impact of digitisation
E initial : geant4 deposit
Neighbouring hit:
hit ? Neighbour’s contribution
no hit ? Creation of hit from charge spread only
+ noise σ = 100 eV, minus dead areas : 5 pixels every 42 pixels in one direction
All contributions added per pixel
+ noise σ = 100 eV
What remains in the cell after charge spread assuming perfect P-well
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

16. Device level simulation
Physics data rate low – noise dominates
Optimised diode for
Signal over noise ratio
Worst case scenario charge collection
Collection time.
Using Centaurus TCAD for sensor simulation + CADENCE GDS file for pixel description
Collected charge
Signal/noise
0.9 μm
1.8 μm
3.6 μm
Distance to diode
Distance to diode
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007

17. Digitisation procedure
%Einit
Einit
Geant4 Einit
in 5x5 μm² cells
Apply charge spread
Eafter charge spread
Register the position and the number of hits above threshold
+ noise only hits :
proba 10-6  ~ 106 hits in the whole detector
BUT in
a 1.5*1.5 cm² tower : ~3 hits.
Importance of the charge spread :
Add noise to signal hits
with σ = 100 eV
(1 e- ~ 3 eV  30 e- noise)
Sum energy in
50x50 μm² cells
Esum
Nigel Watson / Birmingham
EPS'07, 19-Jul-2007