1. Requirements and Specifications for Si Pixels Sensors
in a CLIC Vertex Tracker
A First Assessment
M Battaglia
CLIC WG-4 Meeting,
CERN, April 22, 2010

2. Physics Motivation eTag = ebN (with N=2,4)
e+e-gH0A0gbbbb at 3 TeV
Multiple b and t quarks expected as main
distinctive signature of many of the CLIC
flagship physics processes (SM, SUSY, …)
Signal cross sections often only O(1 fb)
and S/B ~
eTag = ebN (with N=2,4)
 Need efficient b tag with low misid;

3. Track Extrapolation Resolution
Space Granularity
Track Extrapolation Resolution
e+e-gH0A0gbbbb at 3 TeV
Imp. Par. Significance of Secondary Tracks

4. Track Extrapolation Resolution sIP
Space Granularity
Track Extrapolation Resolution
sIP
VTX standalone
Imp. Par. Resolution
Given CLIC constraints this can
be achieved with a multi-layered
VTX with single point resolution
~ 3 mm, i.e. a ~ 10 mm binary pixel
or a mm analog pixel with
charge interpolation

5. Single Point Resolution
Space Granularity
Single Point Resolution
spoint vs. ADC bits for CMOS pixels
active thick ~15 mm, pitch 40 mm
spoint vs. pixel pitch for CMOS pixels
active thickness ~15 mm, S/N ~ 20
spoint vs. S/N for SOI pixels
active thick ~30 mm, pitch 10 mm
Many ways to get to spoint ~3 mm,
mostly technology/readout dependent,
two track separation also important.

6. Machine-induced Backgrounds
Hit Density from incoherent pairs on VTX
vs time from start of train
GuineaPig
+MOKKA G4 Simulation
A Sailer
Radius
Pairs
gg g hadrons
31 mm
hits mm-2 ns-1
hits mm-2 ns-1
43 mm
hits mm-2 ns-1
hits mm-2 ns-1
61 mm
hits mm-2 ns-1
hits mm-2 ns-1
Need safety factor of 5-10
A Sailer + MB

7. Cluster Characterisation
Detector Occupancy:
Cluster Characterisation
Real Low-energy e- Clusters
on CMOS Pixels
Simulated Track Path Length
in 50 mm of Si
Clusters in CMOS 15 mm Pixels due to
low energy electrons from 1.5 GeV e- beam on Al scraper
at LBNL ALS
High pt Tracks
Pairs
MB et al., IEEE TNS 55 (2008)
De Masi,TIPP09
Expect hits/mm2/ns, but depending
on technology and layout each hit spreads
over few to > 10 pixels

8. Detector Occupancy MOKKA G4 Simulation + Marlin Reconstruction
Overlay pair hits to 3 TeV e+e- events and
study standalone VTX pattern recognition
efficiency/purity vs time stamping.
20 mm pixel, single hit efficiency 99.5%
Efficiency for reco tracks with pt>0.5 GeV
MOKKA G4 Simulation
+ Marlin Reconstruction
(Very Preliminary)
Quality Cuts:
Trk Fit Prob > 0.1%
Nhits > 3
No outlier hits
At least one hit on innermost layer

9. Detector Occupancy 40 mm pixel pitch 20 mm pixel pitch
Requirements in terms of space granularity from
occupancy and single point resolution are comparable

10. Material Budget: Si and Support 0.282% X0
STAR Low mass carrier: 50mm CFC+3.2mm RVC+50mm CFC (=0.11%X0);
Impact Parameter
Component
Thickness (% X0)
50 mm Chip
0.054
Adhesive
0.014
Kapton Cable
0.090
Carrier
0.110
Total
0.282
Sensor Thickness mm a mm b 25
3.5
8.9 50
3.7
9.6
125
3.8
11.7
300
4.0
17.5

11. Power Dissipation and Cooling
Material Budget:
Power Dissipation and Cooling
Material minimisation dictates passive cooling,
Preliminary tests with thin monolithic CMOS sensors on CFC ladder support structure
in collaboration with STAR HFT indicate that 1-3 m/s airflow removes mW/cm2
without inducing large vibrations.
Assuming power dissipation to be
concentrated at the end of column,
20 mm pixels and 1 cm column height,
this corresponds to a limit of
~0.15 mW/column
This power budget appears to be
realistic for a variety of monolithic
pixel sensor technology, but is/will
this be feasible when including
time-stamping capabilities ?
Is power pulsing at 50 Hz an option ?
IR Camera Image
Air Cooling Test
Thin Chips
Heating cable
(80mW/cm2)
T(0C)

12. (Cluster multiplicity
Data Rates
Preliminary estimate
from hit rates
(Cluster multiplicity
= 2.5 high p trks | = 5 pairs)
physics
150 hits/layer
2500 pixels
gg g hadrons
100 hits/layer/ns
1500 pixels/ns
pairs
1900 hits/layer/ns
25000 pixels/ns
CLIC ~190 Mpixels /s
~1-2 GB/s
Mpixels /s
250 MB/s

13. Expect significant effort in detector benchmarking with physics, layout optimisation,
machine-induced background studies and reconstruction/analysis tools in the next
6 months (WG-3), which will better define granularity requirements;
Some studies will include digitisation (need guidance on assumptions);
Realistic material budget (sensor thickness, support structure, services, cables and
connectors….) will be essential to these studies (again need guidance);
Significant cross-feed of information and test configurations ahead of data production
for simulation physics studies.