Connections between Vertex Detector and Beam Delivery System

1. Connections between Vertex Detector and Beam Delivery System Chris Damerell 30 July 2003 • Topics: • Beampipe radius and thickness • Beam-associated RF pickup • Radiation backgrounds • Access to inner detector region • ‘Final Focus Lab’ • Conclusions – the way forward Daresbury LC Opportunities – Chris Damerell

2. Beampipe radius and thickness Rbp = 12-15 mm (NLC, TESLA) Daresbury LC Opportunities – Chris Damerell

3. 4 layer, dble 5 layer • Beampipe radius important where low mom trks need to be well measured (charm tag, B vertex charge) • Difficult to quantify in context of future TeV-scale physics, but there are numerous historical examples: • UA1 ‘top’ at 40 GeV (Proc. SLAC Summer Institute, 1984, p 45) • LEP Higgs • SLD Bs mixing Daresbury LC Opportunities – Chris Damerell

4. Andrei Seryi and John Jaros at Cornell workshop 14 July: • Based on conclusions of Chao study from 1.5 years ago … • Meanwhile, studies of Xella, de Groot, Wing and Kuhl reported in numerous workshops • One cannot argue that luminosity or backgrounds should be compromised • Collimator wakefields are • (A Seryi) so the large-L* option has some negative aspects • If large radius beampipe is price of this FF design, should at least be considered carefully • Aim to avoid a design path for which Rbp expands exponentially till startup … Agreed that VX radius is, in certain extents, a free parameter that accelerator physicists can optimize Daresbury LC Opportunities – Chris Damerell

5. Detector was re-designed, starting December 1988 With RBP = 25 mm, it was constructed and installed within the following 3 yrs • (a) difference between ‘startup’ and ‘physics’ beampipes ‘like night and day’ • Dec 2, 1988 SLD Adv Gp discussed 16, 18 and 25 mm options • SLC backgrounds proved to be at or beyond the acceptable limit for the SLD drift chamber, so 25 mm was a wise choice • However, the loss of Bs mixing was a high price, as was the loss of a possible Higgs signal at LEP • When SLD was designed, even the synergy between vertexing and beam polarisation was generally dismissed … • How will all this play out at the future LC? Daresbury LC Opportunities – Chris Damerell

6. How about the wall thickness? – coupled to the radius • stabilise delicate inner section of beampipe with robust support shell of vertex detector • particularly important during transportation/installation of ‘R20 module’ in detector • will permit inner section of beampipe wall thickness of < 0.5 mm Be Daresbury LC Opportunities – Chris Damerell

7. Beam-associated RF pickup • SLD experience • tiny signal charges stored safely in 307 million potential wells • DAQ system (PLL loop in optical converter) dislocated by every bunch • EM radiation was not leaking through steel/beryllium; believed associated with ceramic feedthroughs and imperfectly shielded coax cables • Warm machine • As at SLC, can afford to reset electronics after each bunch train • minor incursion into 8 ms DAQ period • low residual pickup during readout can be filtered out, as at SLD, by Correlated Double Sampling logic (q.v.) • this works cleanly for CCD and DPEFET option, not so for HAPS or MAPS. But possible add-ons … • Cold machine • must be actively reading throughout bunch train • 150 BX per frame of layer-1 • pickup immunity a major issue; must be tested in realistic conditions Daresbury LC Opportunities – Chris Damerell

8. Correlated double sampling • CDS is the term invented circa 1972 for the form of pedestal subtraction used to suppress reset noise in CCD front-end circuits • Simplest CDS involves: • Reset sensing capacitor***measure V-out***transfer signal charge***re-measure V-out • Used to reduce the system noise from tens of e- to ~1 e- by suppressing the fluctuations in post-reset V-out • DEPFET shares robust CDS capability with CCD, in LC application: • Read pedestal+signal***reset – ie remove signal Q***read pedestal alone • However, MAPS CDS involves progressive signal integration over full frame period of 50 ms or whatever, cf 20 ns for CCD CDS • Problem could in principle be solved by incorporating 1-pixel CCD, or DEPFET structure, within the CMOS pixel • CDS with Dt = 50 ms? • SLD was OK in inter-train period with 200 ms CDS sampling period, and ERF (q.v.) • might get away with it at NLC, after some settling time • might not work at TESLA due to RF activity within train Daresbury LC Opportunities – Chris Damerell

9. Extended row filter, SLD Daresbury LC Opportunities – Chris Damerell

10. Effectiveness of ERF in suppressing ‘noise’ hits (including pickup in operational conditions in SLD barrel between bunch trains) Daresbury LC Opportunities – Chris Damerell

11. Radiation backgrounds • Estimates were stable for some years: •  50 krad/year (e+e- pairs) •  109 neutrons/cm2/year • these figures would probably be acceptable for all VTX options, with the caveat that R&D on radiation effects in pixel detectors is rudimentary, and there are still surprises (Olga Igonkina results reported at Cornell) • For gamma-gamma option, a bombshell reported at Cornell: • electron beams are highly disrupted by lasers • beams with large energy spread can’t be dumped cleanly • inner two layers of VTX have line-of-sight to main beam dump • see 1011 neutrons/cm2/year !! • may leave only the HAPS option standing, severely compromising LC heavy flavour physics for gamma-gamma • Second indent • again • again • again • Second indent • again • Title • Trick to getting a new line with arbitrary indent appears to be to make a CR followed by delete to remove the unwanted bullet. Then copy a line that has the desired indent and paste where you want it. Despite fact that you can’t select the bullet, it appears in the correct place when pasted. For example: • Second indent NOTE:Lower neutron rate at gg IR than LHC Daresbury LC Opportunities – Chris Damerell

12. Access to inner detector region How to access inner detector system?? Bill Ash as late as 1989 swept away a dreadful plan with a brilliant new idea … Daresbury LC Opportunities – Chris Damerell

13. Procedure agreed also for TESLA (and NLC detectors), despite initial concerns from Ron Settles – remember, LC tracker will be ~ 6 m long Daresbury LC Opportunities – Chris Damerell

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17. Entire operation took 2 months, late October-December 1991 • For the upgrade VXD2-VXD3, we removed a ton of cables • For LC VTX, will also eliminate all inner electronics – endcap tracking should be beautiful at last • Access to the ‘R20’ region will remain essential • SLD procedure is now universally (?) accepted Daresbury LC Opportunities – Chris Damerell

18. ‘Final Focus Lab’ • Suggest ‘no beam’ FF lab somewhere in the world (eg Daresbury) • will have an unprecedented density of high tech instrumentation • 800 million channels of some silicon pixel technology, read every 50 ms during the bunch train (TESLA) may be non-trivial! • more generally, issues of mechanical (eg vibrational), thermal and electromagnetic interference • currents on wires in beampipe won’t generate the highest frequency RF, but probably enough (Marty B, Marc R, Clive Field, Jerry VaVra) • ceramic feedthroughs, imperfectly screened coax, are main RF sources identified so far. These may be more distant in LC, but there are many other factors, like warm or cold machine, FONT or not, … Daresbury LC Opportunities – Chris Damerell

19. Synergy with other science • Pixel detectors are uniquely inter-disciplinary • Example from ‘fall of the wall’ in structural biology (J Hajdu, TESLA colloquium) • 120 Hz frame rate needed at LCLS (with 14 bit dynamic range) • SNAP (600 Mpixels), XEUS, biological cell imaging (CPCCD mentioned 4 times in London meeting on 24 June, … • Fast Gigapixel-scale imaging systems are widely needed for science, and the LC vertex detector community is making a strong contribution to their development Daresbury LC Opportunities – Chris Damerell

20. Conclusions – the way forward • BDS design should help build the platform for unique heavy flavour physics capability at the LC (hence SUSY, extra dimensions, bosonic supersymmetry, etc) • BDS and VTX systems are ‘joined at the hip’, hence each can help the other, or render the other inoperable … • Historical precedents for both cases exist • don’t dismiss each problem with the escape clause: • “One can still use [one of CCDs/MAPS/HAPS/diamond detectors/…]” • some may be only dreams; all have their Achilles heels. Be careful not to get painted into a corner. The ‘paradigm shift’ from strips to pixels is in its infancy – limited experience with pixel-based vertex detectors is worrying! • Main issues/risks: • beampipe radius • radiation background, notably neutrons • pickup immunity (a major headache if TESLA) • Avoiding the inferno at heart of LHC gives the LC a major physics advantage (or complementary reach) • We should not erode this by an unbalanced design strategy – physics was lost at LEP and SLD through insufficient control of small-radius backgrounds • These lessons should have been learned. By working closely together, the BDS and VTX communities can prepare for stunning physics discoveries at the LC Daresbury LC Opportunities – Chris Damerell

21. Neil Calder at Cornell workshop: supply the best 60 second answer. Daresbury LC Opportunities – Chris Damerell