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30 July 2003Daresbury LC Opportunities – Chris Damerell 1 Connections between Vertex Detector and Beam Delivery System Chris Damerell 30 July 2003 Topics:

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Presentation on theme: "30 July 2003Daresbury LC Opportunities – Chris Damerell 1 Connections between Vertex Detector and Beam Delivery System Chris Damerell 30 July 2003 Topics:"— Presentation transcript:

1 30 July 2003Daresbury LC Opportunities – Chris Damerell 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

2 30 July 2003Daresbury LC Opportunities – Chris Damerell 2 Beampipe radius and thickness R bp = mm (NLC, TESLA)

3 30 July 2003Daresbury LC Opportunities – Chris Damerell 3 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 B s mixing 4 layer, dble 5 layer

4 30 July 2003Daresbury LC Opportunities – Chris Damerell 4 Agreed that VX radius is, in certain extents, a free parameter that accelerator physicists can optimize 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 R bp expands exponentially till startup …

5 30 July 2003Daresbury LC Opportunities – Chris Damerell 5 (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 B s 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? Detector was re- designed, starting December 1988 With R BP = 25 mm, it was constructed and installed within the following 3 yrs

6 30 July 2003Daresbury LC Opportunities – Chris Damerell 6 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 How about the wall thickness? – coupled to the radius

7 30 July 2003Daresbury 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

8 30 July 2003Daresbury 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 s 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 = 50 s? SLD was OK in inter-train period with 200 s 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

9 30 July 2003Daresbury LC Opportunities – Chris Damerell 9 Extended row filter, SLD

10 30 July 2003Daresbury LC Opportunities – Chris Damerell 10 Effectiveness of ERF in suppressing noise hits (including pickup in operational conditions in SLD barrel between bunch trains)

11 30 July 2003Daresbury LC Opportunities – Chris Damerell 11 Radiation backgrounds Estimates were stable for some years: 50 krad/year (e + e - pairs) 10 9 neutrons/cm 2 /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 cant be dumped cleanly inner two layers of VTX have line-of-sight to main beam dump see neutrons/cm 2 /year !! may leave only the HAPS option standing, severely compromising LC heavy flavour physics for gamma-gamma Second indent 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 cant select the bullet, it appears in the correct place when pasted. For example: Second indent NOTE: Lower neutron rate at IR than LHC

12 30 July 2003Daresbury 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 …

13 30 July 2003Daresbury 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

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17 30 July 2003Daresbury LC Opportunities – Chris Damerell 17 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 Entire operation took 2 months, late October-December 1991

18 30 July 2003Daresbury 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 s 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 wont 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, …

19 30 July 2003Daresbury 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

20 30 July 2003Daresbury 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 dont 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

21 30 July 2003Daresbury LC Opportunities – Chris Damerell 21 Neil Calder at Cornell workshop: supply the best 60 second answer.


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