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

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

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

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

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

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

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)

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

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

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!

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

With Thanks… Introduction Timepix LHCb Upgrade Testbeam Telescope