1. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 1  Developments since 13 May meeting  Outcome of review on 24 June  HPD planning  MaPMT planning D.Websdale Meeting with LHCC referees CERN, 1st July 2002 RICH photodetectors – status and planning

2. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 2  Pixel chip measurements at 40MHz  HPD: absolute measurements of thresholds and photoelectron detection efficiency  Bump bonding developments  MaPMT – magnetic field measurements Developments since 13 May meeting

3. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 3 LHCb pixel chip tests Ken Wyllie at al 40MHz lab system to be adopted as global system for all tests – chips, wafers, assemblies, anodes, HPDs Limited functions at the moment – problems with memory access on FLIC, under investigation Restricted event size – use LHCb mode = 1024 pixels

4. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 4 Threshold and Noise scans at 40MHz Threshold ~ 1130e- RMS ~ 110e- Noise ~ 140e- (~130e- @ 10MHZ) Noise and threshold characteristics satisfy LHCb RICH requirements Threshold < 2000e Noise < 300e

5. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 5 Pixel HPD (480 units) 80mm photocathode window Electron Optics: 20 kV 5 x demagnification 1024 super-pixels 0.5mm x 0.5mm PIXEL HPD PGA ceramic carrier Kovar ring Bump- bonded chip assembly

6. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 6 Response to LED – silicon bias and HV Detector bias scanHigh voltage scan  ´= 1.741 @ 19kV, 80V

7. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 7 HPD -Threshold distribution Gaussian fit: m = 6.76kV (<1880e)  = 0.82kV (230e) Gaussian distribution reflects the comparator threshold distribution of the ALICE1LHCb chip (without threshold adjust) Differential number of firing pixels as a function of HPD HV (Si det. bias = 80V)

8. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 8 Photoelectron detection efficiency(1) Poisson fit  = 2.6 @ 19kV,80V  ´= 1.74 @ 19kV,80V Number of firing pixels per LED pulse Back-pulse spectrum  = average number of photoelectrons per LED pulse inferred from back-pulse fit

9. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 9 Detached bump bonds Responding pixels: 70% (Am, in HPD) Responding pixels: 94% (Sr, on bare anode) The principal cause of low efficiency is detached bump bonds

10. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 10 Photoelectron detection efficiency(2) LED shining smaller pixel area, where bump-bonds are generally good: Analyze event size, infer  ’ from P(0) Correct for double pixel clusters

11. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 11 Photoelectron detection efficiency(2) Record back-pulse spectrum, infer  from fit; problems at low ADC channels under investigation. Compare values of  ’ and  ; present estimates range from 81% to 83%; not corrected for LED drift with time, LED tail, missing bump-bonds, masked pixels, photoelectron pile-up Error estimates: LED drift: 5-10% Fit parameters: 5% LED tail: a few %

12. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 12 Bump-bonding problem Possible causes Three main differences between Omega3 (half-scale prototypes) and ALICE1LHCb (full-scale prototypes): bake-out temperature lower, dwell time shorter elongated bump shape increased die size and thickness elongated bump shape does not correspond to relaxed shape when bumps re-melt expansion coefficient mismatch between Si (3.5 ppm/  C) and alumina (7 ppm/  C) results in electronics chip downwards bending: calculated sagitta with 2D bimetallic strip model: ~30  m at 300 ° C for 15mm-long die; goes with the square of the die size bump-bond diameter is 32  m BUT no major degradation of bumps after silver glass curing process (dwell plateau 400 °C, dwell time ~10 min.) incomplete curing process of silver glass, which could possibly experience further non-uniform retraction during subsequent bake-out cycle metallurgy problems (UBM=Under Bump Metallization) ) resulting in degraded bump adherence

13. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 13 New assembly measurements(1) Example with assembly 73: Before bake-out: 6 missing bumps After bake-out: 33 missing bumps

14. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 14 Testing new bump bonded assemblies Sr source: response table: Number of Responding pixels from 8192 [%] Before bake-outAfter bake-out 8186 [99.93%] 8159 [99.60%] 8178 [99.83%] 8179 [99.84%] 8191 [99.99%] 8191 [99.99%] 8171 [99.74%]NA 8188 [99.95%]NA New bump-bonding process better than ever; New, unpackaged, bump-bonded assemblies completely survive bake-out cycle;

15. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 15 Bump bonding – road map to solution Bake out sensor–chip assemblies IF detach  Modify bonding process (VTT) IF survive: Bake out anode carrier assemblies IF survive  Resume HPD production (DEP) IF detach: Test following (4 month programme) Stiffened ceramic carrier Ceramic with lower thermal expansion coeff Different glue Partial surface glueing

16. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 16 HPD project – status First HPD prototype Systematic measurements with pulsed LED show expected photoelectron response… with the exception of the missing bump-bonds New HPD preparation On hold at DEP Bake-out tests of bare new LHCb assemblies from VTT successful Wait for bake-out tests of packaged new LHCb assemblies from VTT to proceed New LHCb chip functional at 40 MHz; Detector order approved and to be placed, mask and wafer layout to be started soon New ceramic carrier mechanical draft design delivered; routing design underway

17. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 17 Longitudinal axis MaPMT - Magnetic Field Tests RICH 1 likely in magnetic field of 400 Gauss Measurements of MaPMT sensitivity to longitudinal and transverse magnetic fields up to 35 mT (350 Gauss) LED light source, APVm read-out B [mT] vs I [A]

18. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 18  -metal shielding 0.9 mm thickness extension 13 or 20 mm shielded MaPMT 13 mm extension Longitudinal B-Field MaPMT with mumetal functions in longitudinal field up to 10 mT (100 G)

19. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 19 Transverse B-Field Transverse field in x-direction MaPMT insensitive to transverse fields up to 25mT (250 G)

20. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 20 RICH Photon Detector review (24 june) June 2002 Milestone: HPD with encapsulated LHCb-ALICE pixel chip 95% working channels Threshold < 0.4 signal (2000e) Noise < 0.15 threshold (300e) LHCb pixel chip working at 40MHz Threshold, noise performance as above If failure – switch to MaPMT Small print – review if LHC delayed

21. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 21 RICH Photon Detector review (24 june) Outcome of Review:- Recommendations HPD: Solve bump bonding problem Delay HPD Milestone until end 2002 If failure – switch to MaPMT If success – produce small series of HPDs - prepare 40MHz anode assemblies MaPMT: Front-end chip is critical item Prepare fully functional BEETLE designs for submission in October 2002

22. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 22 RICH Photon Detector history Dec 1999:Pixel HPD chosen as baseline from 3 options “Lowest risk within budget” Dec 2000:Milestone: Working HPD Missed:Pixel chip limited to 10MHz Sept 2001:Milestone: HPD with 10MHz chip Missed:Delays in bump-bonding and anode assembly June 2002:Milestone:HPD with 10MHz chip + Working 40MHz chip Missed:Bump bonds detached during bake-out

23. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 23 RICH Photon Detector history Dec 1999:Pixel HPD chosen as baseline from 3 options “Lowest risk within budget” Dec 2000:Milestone: Working HPD Missed:Pixel chip limited to 10MHz Sept 2001:Milestone: HPD with 10MHz chip Missed:Delays in bump-bonding and anode assembly June 2002:Milestone:HPD with 10MHz chip + Working 40MHz chip Missed:Bump bonds detached during bake-out Months (anticipated) To LHC collisions 66 54 57

24. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 24 HPD planning – short term Short term tasks:CERN group (3-4 FTE) + RICH team testing June – Dec 2002: Solve bump bonding problems: Bake out anode carrier assemblies IF survive  Resume HPD production (DEP) IF detach: Test following (4 month programme) Stiffened ceramic carrier Ceramic with lower thermal expansion coeff Different glue Partial surface glueing Milestone: End 2002 Demonstrate HPD with 10MHz chip satisfying all technical criteria IF Failure  switch to MaPMT

25. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 25 HPD planning – medium/long term Medium term tasks:CERN group (3-4 FTE) + RICH team testing Jan – March 2003: Complete small (~4HPDs) series production: Produce and verify 40MHz anodes April – October 2003: Complete 40MHz HPD prototyping Prepare specs/invite tenders for anodes and tubes Milestone: Dec 2003place orders for tubes Long term tasks:CERN group (3 FTE) + Glasgow/Edinb. (4-5FTE) March 2004-March 2006: Produce and test HPDs Install HPDs Milestone: Sept 2006commissioning completed

26. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 26 MaPMT readout MaPMT: (225k channels) Readout options: 1.Binary (as now)5.5CHF/channel 2.Digital (as ITR scheme)7.5 CHF/channel 3.Analogue (as VELO scheme)10 CHF/channel Critical item for all is the front-end chip BEETLE is preferred LHCB compatible chip BEETLE needs reduced (x ~50) gain Options to reduce gain: Charge attenuator at pre-amp input Voltage attenuator at shaper input Reduced pre-amp gain Reduced PMT HV Reduced number of PMT dynodes

27. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 27 MaPMT planning Tube production and testing: March 2004-March 2006 is not on critical path Front end chip with appropriate gain is critical component. PMT readout demonstrated at 40MHz with APV chip, but not LHCb compatible PMT with attenuator + BEETLE pre-amp/shaper demonstrated BEETLE is preferred chip – valid for binary, digital or analogue readout schemes Next steps: Short term tasks: Edinburgh, Oxford (+Heidelberg), Cambridge July – Dec 2002: Planning meeting 15 July Prepare designs for fully functional BEETLE, adapted for MaPMT Submission for Multi-Project Wafer run in October 2002 Medium term tasks: Decision on readout mode (costs are compared to HPD + readout chain) Binary preferred - uses same readout chain as HPD Digital - use Inner tracker readout scheme Analogue - use VELO readout scheme Install HPDs Milestone: Sept 2006commissioning completed

28. D.Websdale, LHCC referees meeting, CERN, 1-7-2002 28 Summary The 40 MHz pixel chip appears to work The bump bonds intrinsically survive the bake out if a problem remains it is related to the packaging in the carrier The prototype HPD functions as expected in all respects (modulo detached bonds) Sufficient time remains to complete the project provided the bump bonding is solved by end 2002 Resources will be found to produce and test a fully functional BEETLE, with appropriate gain for MAPMT, for early 2003. The MaPMT remains a viable backup.