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Timepix and LHCb Upgrade RICH Photon Detectors. Timepix technology in an LHCb upgrade context Richard Plackett – CERN Medipix Group Medipix Group Meeting, CERN, 24 th September. Overview. Introduction to RICH detectors LHCb RICH System MCPs as an LHCb RICH photon detector - PowerPoint PPT Presentation
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Timepix and LHCb UpgradeRICH Photon DetectorsTimepix technology in an LHCb upgrade context
Richard Plackett – CERN Medipix GroupMedipix Group Meeting, CERN, 24th September
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Overview
Introduction to RICH detectors
LHCb RICH System
MCPs as an LHCb RICH photon detector
Advantages and Disadvantages
Introduction
RICH Detectors
Pros & Cons
MCPs
Presented to RICH upgrade meeting, 13th August
LHCb RICH
-3-
LHCb Layout
• LHCb is a spectrometer looking in the ‘forward angle’• Ring Imaging CHerenkov (RICH) detectors identify particles
with high accuracy
RICH1
RICH2
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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Finding Kaons• The b-c-s chain means ‘interesting’ events will contain one or
two Kaons (strange quark mesons)
• Finding the Kaons in the Pion background is very difficult as they have very similar mass
• RICH systems have the sensitivity to do this but are technically quite challenging and only operate over a limited momentum range
b
W-
c
W+
s
u
K-
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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Cherenkov Angle
Cherenkov angle
The Cherenkov angle is related to a particles speedFrom special relativity, if you know its momentum you can find its massBy measuring the Cherenkov angle we can identify the particle
The waterfronts produced as the particle passes interfere constructively rather than destructively
This produces a Cherenkov photon at a specific angle
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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RICH Detectors• The cone of Cherenkov light is focussed to a ring with a
spherical mirror• The diameter of the ring is proportional to the particles' speed
Charged particle
Spherical Mirror
Cherenkov angle
Photon Detector Plane
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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LHCb RICH System• Contributions to uncertainty: Emission point error, chromatic
aberration, spherical aberration, track error, pixel pitch
• Key parameter is the photon detection efficiency as currently between 4 and 30 photons detected per track
CF4 radiator
Beampipe
Spherical Mirrors
Flat Mirrors
Photon Detectors
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
Flat Mirrors
Aerogel
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RICH1 Photos
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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RICH2 Photos
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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RICH Upgrade Plans• Baseline to keep current 2 RICH geometry and simply upgrade
current HPD photo detector planes
• We can’t change the photo-sensitive area as the chromatic and spherical uncertainties have been optimised
• Also a suggestion for a 2 gas ‘superRICH’ in the RICH2 position and a Time of Flight covering low momentum presently covered by the aerogel in RICH1 (TORCH)
• Currently Hammamatsu MAPMTs are strong candidates, but suffer from cross talk and no obvious 40MHz readout solution yet
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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TORCH• Completely new Sub-detector for Particle Identification• Time of flight detector planning to use MCP tubes from
Photonis (Burle)• Requires lower granularity than RICHs but ~50ps timing on hits
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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Proposed 40MHz Chip• LHCBPIX2? VELOPIX?
currently many names
• Most probably – 55um square pixels – 256 by 256 matrix (14mm square)– 40MHz readout– On chip zero suppression– 4 side tiling with through silicon via technology – Worst case 800um inactive periphery on one side– On matrix cluster analysis a la Medipix3
• Still in design phase so some flexibility
• Well defined development path through Medipix3 and Timepix2, so there will be ‘prototypes’ available early.
Timepix readout chip
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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MCP Photon Detector
Quartz window and photocathode as HPD and MAPMT
200V/mm drift field
MCP cascade amplification (~1kV)
Bare readout chip array (no bump bonds)
Ceramic carrier with possible cooling built in
Photon
Photoelectron
Electron shower
0.5mm
0.5mm
Proximity focused MCP tube with 55um pixel readout
Tuning the lower drift field allows the electron shower profile to be well controlled
10um pores in an MCP
Cascade amplification similar in principle to a PMT
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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Photon EfficiencySimilar to current RICH HPD *IF* packing fraction is high enough
Effect HPD MCP
Photocathode ~33% ~33%
Packing Fraction ~67% ~85%
MCP acceptance ~65%
Detection efficiency ~85% ~100%
A square device is possible….85% is an 5mm gap round a 4 by 4 chip active matrix
And indeed so are COMPASS RICH / MaPMT style lenses
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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MCP Advantages• High Magnetic Tolerance, could operate in RICH1 (600G)
without ANY shielding – no flat mirrors?
• Pixel readout chip eliminating crosstalk, photon counting, working at 40MHz etc
• A fast (~100ps) signal could also be produced with a secondary readout system to allow ring time separation
• No ‘first dynode’ noise from capillary so 0 to 1 photons discrimination relatively easy
• ‘Chevron’ style MCPs are resistant to ion feedback
• Essentially a flat panel detector few cm deep detectors.
• Only requires ~1kV supply
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
-16-
Magnetic Field ToleranceMagnetic field tolerance comes primarily from the short flight path of photoelectrons and electron cascade and resultant high electric fields
“The present Burle 85011 MCP with 25 um pores works well in fields up to 0.8 T (NIM A 567 (2006) 124–128 )”
This is an order of magnitude better than we currently need (0.06T unshielded in RICH1).
The design of the Berkley groups photon counting MCP And a photo of the same
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
-17-
Some images from John’s tube
Images Presented at SPIE 2008 in Marseille
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
-18-
Fast Signal Readout• Intrinsically MCPs are fast photon detectors operating around 50-100ps
• Incorporating this into the pixel chip would incur a big power penalty, which would affect the design of the tube (cooling etc).
• A whole tube readout based on MCP current could be implemented in addition to pixel chip possibly using something like the gridpix technology developed by Harry van der Graaf to produce larger timing pixels
Taken from a presentation to the ATLAS Tracker Upgrade Workshop, Valencia, Dec 12, 2007
Here a grid is mounted over a Timepix readout chip for the InGrid project
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
-19-
MCP Disadvantages• Not an off-the-shelf system, but could be close, relatively
simple encapsulation with no bump bonds. John Vallerga is currently working with Hamamatsu to incorporate Timepix chips into their MCPs.
• To instrument same area as current RICHs gives far too many channels, although this compensates for limited chip occupancy and helps dead time. With a proximity focusing system 4m2 gives ~1billion channels, eg a 4 by 4 chip tube would require ~500 tubes
• MCP capillaries have a ‘recharge’ time, but this is mitigated by the overabundance of pixels and capillaries.
• Ageing (next slide)
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
-20-
MCP Ageing
Lifetime of the MCP coating is measured as extracted charge Approx lifetime is 1 Coulomb/cm2. Assume a gain of 10000e- per event. With 6x1014 events/cm2 as a lifetime, Gives18 billion events per 55 micron pixel
Assuming 150 tracks per event and 25 photoelectrons per track and 4 square meters instrumented gives a 10 year lifetime
(ok so I assumed the Cherenkov light was uniformly distributed too)
The plate itself is made from coated lead glass. The electron cascade amplification ablates away the coating giving an ageing effect.Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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RICH MCP Summary• MCP phototubes have the potential to perform with similar
photon efficiency as current HPDs but with very high tolerance to magnetic fields, reduced volume and HV requirements.
• 40MHz pixel chip being considered for VELO upgrade (Timepix or FPIX) and may allow common readout systems and development cooperation.
• A fast readout scheme could provide additional information for ring finding etc in the RICH… and even be used for the TORCH.
For more information on John Vallerga’s hybrid pixel MCP tubes…
NIM A 567 (2006) 110-113 ‘ A noiseless kilohertz frame rate imaging detector based on microchannel plates read out with the Medipix2 CMOS pixel chip’
Astrophysics and Space Science (2008), p98 ‘The current and future possibilities of MCP based UV detectors'
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH
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What Next?• We should do what we can to make it easy for the RICH group to make a
decision, provide support and effort where needed as with VELO
• Will be harder as at the moment there is less upgrade activity in the RICH groups
• Lots of photon detector activity within the Medipix collaborations anyway, maybe some common effort for prototypes etc would be helpful
• We have some photon detector experience within the CERN group so we will continue to pursue it and see what are feasible options and what aren't…
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Conclusions• If we develop a 40MHz chip for the VELO we could use it in the
RICH photon detectors too
• I have presented the possibility of using MCPs or HPDs in the RICH upgrade meetings and it has started to propagate to other presentations…
• The TORCH proposal also plans to use MCPs so they aren’t an alien technology to the RICH group
• If we can add fast timing to the tube then we have a very good chance of replacing the baseline MAPMT detector
• Being in two sub-detectors of LHCb boosts both projects and increases common effort
• Still need to convince RICH group that its worth the work to develop a VELOPIX based tube with us rather than buying a commercial tube ‘off the shelf’
Introduction
RICH Detectors
Pros & Cons
MCPs
LHCb RICH