1. VELO Decisions Thomas Ruf LHCb week February 2001 Interference with LHC machine   LEMIC, January 2001: Presentation of the VELO Vacuum Chamber design was well received, see also conclusion from A.Rossi.   The subsequent discussion in the LHC technical board was also quite positive (unofficial).  BUT,  BUT, possible request from the LHC machine: Downtime of LHC in case of a worst case accident should be limited to 2 weeks. This means for LHCb: Replace VELO Vacuum Chamber with spare beam pipe RICH1, inner tracker ? continue LHC running without LHCb Detailed planning needs to be worked out how this could happen. Started by M.Ferro-Luzzi in context of risk analysis. Need a spare beam pipe. Fast switch to spare beam pipe needs to be taken into account in design for Station1 and Rich1.

2. VELO Decisions Thomas Ruf LHCb week February 2001 Conclusions Conclusions presented by A.Rossi (LHC-VAC)  The LHC/VAC group accepts: Foil not withstanding atmospheric pressure - compromise between safety and physics performances. 2 phases CO2 cooling system in secondary vacuum.  Provided that: Risk assessment complies with LHC standards. Design developments in close collaboration/supervision with CERN. Prototype and testing prove principles. Replacement of the vacuum chamber in the case of a major accident. Yearly design reviews, 2 day workshops: lApril 2001 lFebruary 2002 lFebruary 2003

3. VELO Decisions Thomas Ruf LHCb week February 2001 VELO Decisions  Sensor choice  Position of Off-Detector Electronics

4. VELO Decisions Thomas Ruf LHCb week February 2001 The VELO Sensor Choice Unanimous decision at the 3rd VELO workshop, 26 January, to adopt n-strip detectors as the baseline for the TDR. Driving arguments for a technology choice are:  Resolution  Signal / Noise  Radiation hardness  Availability  Problem: Cannot get all the good things at the same time.  Find a solution of which we are convinced it will work.  Improvements are still possible at a later time.  Problem: Cannot get all the good things at the same time.  Find a solution of which we are convinced it will work.  Improvements are still possible at a later time. p-strip OR n-strip detectors ? TP: 150  m thin n-strip detectors with 40  m minimal strip pitch since then: trying to prove feasibility and to improve

5. VELO Decisions Thomas Ruf LHCb week February 2001 What do we have tested? n-on-n detectors from HAMAMATSU Thickness: 300  m, Smallest strip pitch: 40  m p-on-n detectors from MICRON: Thickness: 200  m ( 150  m and 300  m exist but not tested Smallest strip pitch: 32.5  m for the r-detector and 24.4  m for the phi-detector p-on-n detectors, DELPHI module, double sided readout: Thickness: 310  m, Smallest strip pitch: 42  m n-side 25  m p-side ( only every second strip read out But LHCb is special: Small strip pitch ! + measurements from ATLAS, CMS, ROSE, … But LHCb is special: Small strip pitch !

6. VELO Decisions Thomas Ruf LHCb week February 2001 Effect of Radiation from Rose collaboration based on diodes NOT directly comparable to strip detectors VELO: ~ 1 x 10 14 n eq cm -2 / year at r=8mm Increase of depletion voltage after irradiation. Lifetime of the VELO is limited by the maximum voltage which the detectors can stand. Because of small strip length and low temperature, the VELO is not limited by the increasing current. Detector will slowly die from inside to outside: The region at r>11mm will last twice as long as the region at r=8mm. depletion voltage ~ d 2  use thinner detectors BUT signal ~ d or run detector not depleted n-type  p-type radiation

7. VELO Decisions Thomas Ruf LHCb week February 2001 What is the difference of a n-strip and p-strip detector after irradiation ? Charge collection efficiency and resolution of an irradiated double sided silicon microstrip detector operated at cryogenic temperatures. Nucl.Instrum.Meth.A440:17-37,2000 Measurements done using a double sided detector If the detector is not fully depleted, charge is spread over a large area on the p-side. Effect only seen for small strip pitches (<100  m) Confirmed by Y2k testbeam results and laser tests. Conclusion: p-strip detectors need to be fully depleted ! double pitch acts as insulating layer n-type  p-type radiation

8. VELO Decisions Thomas Ruf LHCb week February 2001 One word about oxygenated silicon A higher CCE is reached for a lower bias voltage with oxygenated silicon compared to standard silicon. HOWEVER, the voltage, where maximum CCE is reached, is not so much different between oxygenated and standard silicon. Oxygen could help in case of n-strip detectors. Liverpool, G.Casse

9. VELO Decisions Thomas Ruf LHCb week February 2001 What can p-strip detectors offer ? What can p-strip detectors offer ? Or why consider p-strip detectors after all ? p-strip detectors can have smaller strip pitches n-strips need to be isolated. Done by using p-stops, p-spray. Limits minimal strip pitch. p-strip detectors can be made thinner Hamamatsu produces n-strip detectors with 300  m thickness only. BUT, MICRON accepted order for 200  m thin detectors. p-strip detectors are cheaper expected saving ~30% (ATLAS). But money is not an issue. Sensor cost is only 10-15% of total VELO cost.  Physics Study

10. VELO Decisions Thomas Ruf LHCb week February 2001 Optimization Study General Constraints  Alignment, handling of detectors: use 180 0 detectors instead of 3  60 0 detectors as in the TP  reduce outer radius from 6cm to 4.5cm for fitting on 6-inch wafer  reduce distance between stations and increase number of stations 25(17)  RF shield, wakefield guide, secondary vacuum: use RF-box with corrugated structure which acts as RF-shield and as wakefield guide have to use 250  m thick Aluminum, because of maximum pressure and RF penetration

11. VELO Decisions Thomas Ruf LHCb week February 2001 Optimization Study Optimization Study Sensor Geometry Two solutions were proposed:  Conservative detector, 300  m thin r-detector, strip pitch: inner region: 40  m medium region: 60  m outer region: 80  m phi detector: inner region: 40-114  m outer region: 40- 72  m 5 0 stereo angle (strip geometry similar to TP)  Ultimate detector, 220  m thin half the strip pitch to above NOTE: Too many channels ! For realistic design, change strip pitch linearly as function of radius and use floating strips. From testbeam (SCTA chip): S/N  20 with 300  m thin detector  expect S/N  10 for 150  m expect S/N  15 for 220  m Available as p-on-n and n-on-n p-on-n: 32.5  m and 24.4  m exist n-on-n: 32.5  m and 24.4  m ordered The performance of many different designs was studied. A clear improvement was seen by going closer to the beam, r min =8 mm (10 mm)

12. VELO Decisions Thomas Ruf LHCb week February 2001 Optimization Study Optimization Study Performance Multipl. scattering:  ~1/p error on impact parameter  ~   l distance to first material: l~ 1/sin    error on impact parameter  ~ 1/p t (moving closer to beam axis helps) Average decay length errors  Conservative detector B   176  m B  K s J/  236  m  Ultimate detector B   138  m B  K s J/  176  m ultimate detector  20% better realistic detector  10% better ? (existing: p-strip, 200  m, ~30  m pitch) 10 5.6 3.2 1.78 1.0 p t (GeV/c) No error on primary vertex ! TP design: B   : 211  m B  K s J/  : 280  m

13. VELO Decisions Thomas Ruf LHCb week February 2001 How realistic is the simulation ?

14. VELO Decisions Thomas Ruf LHCb week February 2001 Thickness Thickness [220  m - 300  m]  depletion voltage ~d 2  signal ~d  multiple scattering ~  d  multiple scattering ~  d optimization study: d=300  m: acceptable d=500  m: effect seen lifetime of inner detector region ~ 1/d  RF + exit window shield  11.8% X 0 Hybrid/support  1.7% X 0 Silicon  4.0 - 5.4% X 0 Radiation length nn:  HAMAMATSU 300  m tested  new MICRON design aims for 200  m  200  m tested, (~15% less signal as expected, to be understood)  150  m availablepn:  Availability Average = 17.4% - 18.9% X 0

15. VELO Decisions Thomas Ruf LHCb week February 2001 Thickness Thickness RF Shield / Sensors Total Aluminum seen Total Silicon seen Average = 1.05 cm includes 2mm of exit window Average = 0.51 cm

16. VELO Decisions Thomas Ruf LHCb week February 2001 Radiation length Mean without beam pipe: 18.5% X 0 75% of the particles see less than 20% X 0. 5% see more than 40% X 0.

17. VELO Decisions Thomas Ruf LHCb week February 2001 Material seen Particle trajectory: x=y=z=0, =0.1,   0 0 X 0 Si+hybrid = 14  2  300  m = 0.84cm  9% Al(45 0 ) =  2  250  m = 0.04cm  0% Al(90 0) + exit window = 2.5mm  2.8% 11.8% Particle trajectory: x=y=z=0, =0.1,   90 0 X 0 Si+hybrid = 12  2  1.5  300  m = 1.08cm  11% Al(45 0 ) = 14  2  2  2  250  m = 2.0cm  22% Al( 0 0 ) = 250  m/0.016 = 1.6cm  18% Al(90 0) + exit window = 0.25cm  2.8% 54%

18. VELO Decisions Thomas Ruf LHCb week February 2001 RF box, support and cooling frames

19. VELO Decisions Thomas Ruf LHCb week February 2001 Conclusions  The safest solution is to use n-strip detectors.  A possible improved cluster resolution doesn’t justify the use of p-strip detectors.  200  m thin detectors seem not to be mandatory.   Starting with 300  m thick detectors and a minimum strip pitch of 40  m seems acceptable.  R&D will continue to find out if n-strip detectors with smaller strip pitch and/or smaller thickness can be made to work.  The safest solution is to use n-strip detectors.  A possible improved cluster resolution doesn’t justify the use of p-strip detectors.  200  m thin detectors seem not to be mandatory.   Starting with 300  m thick detectors and a minimum strip pitch of 40  m seems acceptable.  R&D will continue to find out if n-strip detectors with smaller strip pitch and/or smaller thickness can be made to work.

20. VELO Decisions Thomas Ruf LHCb week February 2001 Planning  Next steps: n-on-n detectors from MICRON: same design as p-on-n detectors, 200  m thick Status: order placed November’00, Mask finished, first detector expected in April Aim: evaluate performance for comparison with HAMAMATSU n-on-n detectors from HAMAMATSU: final design, phi-detector with large stereo angle, floating strips Contact HAMAMATSU now ! Contact other companies  July 2001 - June 2002: Evaluation of prototypes  July 2002: Review of sensor design, start tendering process  December 2002: Order final sensors  Next steps: n-on-n detectors from MICRON: same design as p-on-n detectors, 200  m thick Status: order placed November’00, Mask finished, first detector expected in April Aim: evaluate performance for comparison with HAMAMATSU n-on-n detectors from HAMAMATSU: final design, phi-detector with large stereo angle, floating strips Contact HAMAMATSU now ! Contact other companies  July 2001 - June 2002: Evaluation of prototypes  July 2002: Review of sensor design, start tendering process  December 2002: Order final sensors Need to have prototype detectors with final design in test beam before submitting the final order.

21. VELO Decisions Thomas Ruf LHCb week February 2001 Position of Off-Detector Electronics Analog transmission over 60m Response is flat up to 10MHz At 40MHz the loss is 2.3 [dB] Lausanne, R.Frei

22. VELO Decisions Thomas Ruf LHCb week February 2001 Measurements with SCTA Lausanne, G.Gagliardi Results  Signal/Noise: 10% less but cable is not the best on the market  Cross talk similar to 8m cable without line equalizer, CF=0.037 Conclusion  Twisted pair cables are a cheap alternative to analog optical links  10m, twisted pair: 48kCHF + connectors  60m, optical: 960kCHF + fibres  60m, twisted pair: 192kCHF + connectors SCTA Header SCTA Data Output of line driver after 60m 1 Mip signals Pickup noise comes from RB2 LHCb note to come