1. Medipix and Timepix chip developments
Recent Measurements with Timepix as a Particle Tracker
Richard Plackett – CERN Medipix Group
VERTEX 2009, Mooi Veluwe, 16th September ‘09

2. Overview
Introducing the Medipix 2 and Timepix Chips Timepix and Time over Threshold Mode Recent LHCb VELO upgrade Testbeam results Timepix Particle Telescope
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope

3. Hybrid Pixel Detectors
Ionizing Particle
Introduction
Timepix
sensor h+
LHCb Upgrade e-
Solder bump bonds
Testbeam
Positive or negative sensor bias
Telescope
Analogue amplification
Readout Chip
Medipix or Timepix in 250um IBM CMOS
Digital processing
Chip read-out

4. Medipix2
Single photon counting readout provides low noise, high contrast images with very high dynamic range
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
55um pixel matrix (256 by 256) reading Si, 3D, CdTe, GaAs sensors
Configurable ‘shutter’ allows many different applications

5. Timepix Timepix is a derivative of Medipix2
Addition of a global clock (up 100MHz) which is propagated to every pixel
Originally conceived for GEM foil detectors
The clock can be used for Time of Arrival (ToA) and Time over Threshold (ToT) modes.
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Threshold
Time of Arrival Mode
Counts from passing threshold to closing shutter
Allows accurate timing of hits in individual pixels

6. Timepix Time over Threshold
Timepix ToT mode is similar in principle to ATLAS pixel..
Preamp has fast rise (90ns) but slow (500ns -2500ns) constant current return to zero
E.g. 20ke- ~1us = 40 x 25ns
Residual errors come from non linearity with small charge signals and a slow return to baseline
Introduction
Timepix
LHCb Upgrade
Testbeam
Threshold
Telescope
Clock
Linearity of one pixel measured at three different threshold values

7. DESY testbeam in November 2006 (A.Bamberger et al)
Timepix GEM foil event
A GEM foil event with a ‘chess board’ ToT & ToA pattern set on the pixel matrix
Introduction
Timepix
LHCb Upgrade
ToA
ToT
Testbeam
Telescope
DESY testbeam in November 2006 (A.Bamberger et al)

8. ToT silicon event Images courtesy of Erik Heijne
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Images courtesy of Erik Heijne
Although conceived for gas detectors Timepix retains the Medipix2 sensor features eg
Pixel leakage current correction
Positive and negative biasing

9. Upgrading LHCb In Addition: The consequence: The Problem:
Muon
The Problem:
LHCb is currently optimised for single interactions, to search for new physics a large increase in statistics is required, significantly complicating the trigger.
HCAL
ECAL
RICH2 TT
Magnet
RICH1
Tracker
VELO
Introduction
Timepix
LHCb Upgrade
The idea:
Aim to operate at L=2.1033
Perform entire trigger on
CPU farm. No hardware
Trigger!
Testbeam
Telescope
In Addition:
A strong case for an upgrade even without SLHC as LHCb does not use all current LHC luminosity
10x increase in Leptonic channels
20x increase in Hadronic channels
The consequence:
Read out all sub-systems
at 40 MHz
Replace all FE-electronics;
all silicon modules,
RICH-HPDs,
FE boards of Calorimeter,
Outer Tracker FE
For more information on LHCb upgrade see the talk tomorrow by JC

10. silicon edge just 7 mm from beam!
LHCb VELO Upgrade
Closest LHC detector to the beam and highest resolution requirements
Currently 21 perpendicular two sided strip planes
Upgrade to strip or pixel system
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
silicon edge just 7 mm from beam!

11. Potential Module Design
Silicon (1-3 pieces) 55x55 mm pixels, 800 mm pixels in areas under chip periphery
Diamond thermal plane with
cutouts immediately above TSV regions
10 Timepix chips
(periphery indicated in white)
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Cooling channel
Power strips and
signal routing area
With a Pixel VELO we can have a low scattering module with high resolution and no strip detector ambiguities

12. Recent Testbeam Activity
Required to demonstrate suitability for tracking
Measure efficiency and resolution
Provide information for VELOPIX design
3 testbeams at CERN SPS with 120GeV Pions
June: as Medipix Group to test Telescope concept
July: Running parasitically from CMS SiBit telescope
August: Running parasitically from EUDET/LCFI testbeam
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Significant improvements to telescope design at each testbeam

13. Timepix Telescope 4 Timepix, 2 Medipix planes in telescope
Symmetric positioning of planes around Timepix DUT
Telescope planes mounted at nine degrees in x and y
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
DUT position and angle controlled remotely by stepper motors
Measurements of resolution with angle, threshold, sensor bias, 3D sensor and timewalk

14. Angled Planes to Boost Resolution
Hits that only affect one pixel have limited resolution (30um pixel region)
Angling the sensor means all tracks charge share and use the ToT information
Introduction
Timepix
55um
LHCb Upgrade
Testbeam
300um
10o
Telescope
Timepix (ToT) tracked position vs cluster reconstructed position

15. Results – Resolution Vs Track Angle
Introduction
Timepix
LHCb Upgrade
Testbeam
Rotation about Y axis
Telescope
2.5um Estimated track contribution to residual
PRELIMINARY: UNCALIBRATED DATA!!
The tracking uncertainty of the telescope is very competitive, with uncalibrated, uncut data, 2.5um is comparable to EUDET running with 30um pixels (timepix is 55um)

16. Results - Residual Width vs Sensor Bias
The residual width shows a clear dependence on orientation as the sensor bias is changed.
This is as expected, and illustrates
the sensitivity of the measurement
The sensor bias was scanned up and down again to ensure any change seen was not a drift
Introduction
Width of y residual
perpendicular
Timepix
LHCb Upgrade
Width of x residual
18 degrees
Testbeam
Telescope
Perpendicular:
As the charge diffusion shrinks you have more single pixel hits, increasing the width of the residual width
High Angle:
As the charge diffusion shrinks you still have a large number of charge sharing hits, holding residual width constant

17. Results – Residual Mean vs Sensor Bias
Varying the sensor bias shows a clear shift in the residual means for highly angled tracks
6 degrees
18 degrees
Introduction
perpendicular
Timepix
perpendicular
LHCb Upgrade
angled
Testbeam
angled
Telescope
Perpendicular:
As the charge collection shrinks you do not affect the position of the reconstructed hit
High Angle:
As the charge collection shrinks you can see the position of the reconstructed hit being pulled

18. Results – 3D Sensors Efficiency Glasgow double sided CNM sensor
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Perpendicular particles passing through a doped hole will deposit less charge in the silicon
The sub-pixel resolution of the telescope allows us to see the efficiency losses due to the anode and cathode holes in the silicon.
Special acknowledgement to Marco Gersabeck who produced this plot and the 3D group at Glasgow who provided the sensor

19. Design Lessons for VELOPIX
Analogue IS better than Binary, even with 55um pixels, even with clusters and charge sharing
Clustering WILL significantly increase hit multiplicity
Interactions within the sensor will occur often and need to be handled to avoid overflowing the chips for that event
From this data we will determine how many bits ToT we need and optimise on chip the data transport
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Timepix (ToT) 5um
Medipix (binary) 11um

20. More Measurements Coming Soon
Lots of data from July and august still to analyse
Resolution as a function of
threshold
2d rotation
Number of bits used
Efficiency and Noise study
Pulse shape reconstructed directly from ToT data
Timewalk measurements
3d sensor
Vertex reconstruction using telescope
Etc…
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Also gain calibration still has to be done with to get optimum performance from TImepix chips

21. In Conclusion
The Medipix2 and Timepix chips are versatile creatures, and are spinning back into HEP
A Timepix like chip is a candidate for LHCb VELO upgrade
At testbeams over the summer Timepix has been demonstrated to run reliably with unexpectedly good resolution
A very large data set has been recorded so expect non-preliminary results soon…
A series of telescopes were developed for these tests. A possible future system could be made available to the community if there is interest … another couple of slides on that …
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope

22. Current Telescope
Successful going on to do a testbeam with SPS collimators
All versions based on the USB interface developed by CTU Prague
Main strength is simplicity, each module powered, biased and read out by USB. DAQ consists of 6 usb lines to a PC and a NIM crate for a pulse-per-second synchronization signal
Data is saved to text files so extremely easy to work with
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
Sensor Bias
timing
USB

23. Limitations
Timing between modules has large uncertainty (500ns) due to the USB readout systems
Long readout dead time (1 second), due to USB 1.1 readout
Either ToT or ToA, as limited number of Timpix chips
Inclined sensor planes good for ToT, bad for ToA as charge sharing clusters can cause timewalk
At current resolution (~2.5um) scattering from PCB is becoming a dominant error
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope

24. Future Timepix Telescope
Solution…
Add an external timing readout to sync systems (and scintillators?)
Replace USB with RUIN, Relaxed or similar (coming soon) allows 100x faster readout over (USB2 or Ethernet)
4 Timepix chips per arm, with one dedicated to ToA
New PCB with cut out behind chip
Possible further upgrade with Timepix2…..
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope

25. Future Timepix Telescope
Results in
High resolution (<3um) as current telescope
Track timing down to 10ns
Link to PMT/external device for trigger and integration of DUTs
Minimum rate 100Hz, max 20kHz
Portable device with text file data output as current telescope
If anyone is interested please let me know
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
DUT
RUIN
RUIN
TIMING

26. With Thanks…
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope