1. Università & INFN Padova
The beginning of Tevatron adventure or the tale of silicon detectors in CDF
Dario Bisello
Università & INFN Padova
Tevatron Day
Padova, 20 dicembre 2011
D. Bisello – Tevatron Day December 20th 2011

2. How silicon detectors changed physics: the search for the top quark
Outline
CDF before Silicon
SVX ( )
SVX’ ( )
SVXII and ISL
Layer 00
Run 2b
How silicon detectors changed physics: the search for the top quark
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3. Birth of the Tevatron & CDF before silicon
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9. First silicons: SVX & SVX’
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10. The Pisa Proposal
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11. First collider silicon detectors
UA2’
UA2’
Si Microstrip Detectors: A New tool for HEP
(E. Heijne, P. Jarron) c. 1981
Silicon pad detectors in UA2: first operation 1987
Mounted directly to the beam pipe
Also: LEP I experiments 1989
CDF not until 1992: widespread doubts whether it would work!
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12. P-775 This was the original collaboration. Look at this schedule!
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13. 1989-90, 1st SVX chips (HP 3.5m technology)
128 channels, double correlated sample, sparse logic.
Soon after: a "rad-hard" UTMC version
Not in time for SVX (eventually put in the SVX').
LBNL constructed all hybrids and modules
Cooling and mechanics in Pisa and FNAL.
Final assembly of modules onto the mechanical structure was done at FNAL.
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14. SVX Two barrels Four layers of silicon DC coupled Electronics rad-soft
Quad sampled
Electronics rad-soft
Major results
B decays were visible – this was a very big deal!
By end of Run 1a, a slight excess in W+jets was observed.
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15. A group coming from SLD and UA1
1990 : Padova enters in CDF
A group coming from SLD and UA1
N. Bacchetta, D. Bisello, G. Busetto, A. Castro, S. Centro (who left soon), M. Loreti, L. Pescara, J. Wyss, L. Stanco (who joined later)
many students (P. Azzi, G. Bolla, R. Rossin, A. Canepa, T. Dorigo, L. Scodellaro, M.P. Giordano, …)
Fields of contribution:
SVX
Data analysis
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16. First recognition of Padova contribution
Padova contributes to:
test beam analysis,
hybrids and chip test,
sensor characterisation
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19. The Ingredients of SVX’
AC coupled strips with FOXFET gate biasing
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20. Early indication of high efficiency, good resolution
= 9 m
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21. Silicon and B tagging
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22. Early event displays IN BEAM COSMIC
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23. “Standalone” Si Tracking in SVX c. 1994
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24. Radiation issues with the FOXFET
bla
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25. SVX’ Lifetime Noise started to increase faster than expected.
CDF Note 3338
Noise started to increase faster than expected.
Believed to be result of FOXFET bias?
Lifetime was reduced by large factors.
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26. CDF II: SVXII, ISL, Layer00, Run IIB
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28. SVX II Started around same time as SVX’ in 1991
The most challenging CDF silicon detector
Significant overlap with SVX and SVX’ Groups
Sensors – Padova, Purdue, Tsukuba, …
Hybrids – LBNL (C. Haber, M. Garcia-Sciveres…)
SVX3 chip (FNAL/LBNL/Padova)
Mechanics a major achievement!
Alignment of all strips parallel to beam to within 100 rad for the SVT trigger!
SVT – a level 2 displaced track trigger
Originally designed to be 4 layers almost immediately upgraded to 5 layers
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29. CDF SVX II SVXII is extremely compact and complicated:
3 Barrels: Very Compact design:
Electronics mounted directly on silicon to avoid longitudinal gaps.
Overlaps in 
Radial span ~8 cm for 5 layers !
SVXII is extremely compact and complicated:
5 double-sided layers in a radial span of ~ 8 cm !
Electronics on the silicon to eliminate gaps in z and r(There was not enough space to stagger them in z)
Because it is in the trigger, and in particular, because only the axial strips are used in the trigger - parallelism of strips is extremely important.
The luminous region in CDF will have 15 cm <  < 25 cm ! In 2D, if the strips are not parallel to the beam, tracks from multiple interactions will appear to be displaced even though they are not.
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30. Radiation and technological issues
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31. Hamamatsu & Micron Run 2 Sensors
Making the CDF sensors was a major effort
Double-sided, some double metal etc.
Micron
~5-6 people permanently residence in Shoreham
Group leaders rotated visits, every 2 weeks
Major review meetings every 2 months
HPK
No direct involvement required but…
Also had trouble making ISL sensors
“We will finish your order, but we will never make double-sided sensors again.” Yamamoto
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32. SVXII Barrels Pictures clockwise from upper left:
End view of an SVX barrel ( 1 of 3 total ) in which the 5 layers are seen, and in particular the ledge structure of the Be bulkheads.
The side view showing the outermost layer silicon and in particular the rail supports. The barrel was being prepared for installation of its outer C Fiber shell.
After the outer screen was attached, the optical hybrids (portcards) were installed in a single shell layer and connections were made.
After tests were complete and no problems were found, the barrel was installed in its space tube which here is supported by an Al cradle in the final assembly rail system.
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33. SVT Operation Commissioning Run (October 2000) – SVT standalone
random
good tracks m
cuts
Commissioning Run (October 2000) – SVT standalone
ALL hits used (no COT track). No real alignment.
The SVT found good tracks with pretty good resolution
Worked pretty much right out of the box!
This plot shows the tracks found by the SVT when running on all silicon hits. There is a clear good track peak with good IP resolution considering the lack of alignments. In Run 2 we will use the drift chamber tracks to seed the hit search and the background of random fake tracks will be very low. Our conclusion is that the SVT works !
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34. IFT and Straws vs ISL and COT
CDF planned to build a fiber tracker to bridge from the silicon to the outer straw tubes
Both the fibers and the straws got cancelled !
Reviews (in 1996) recommended the COT and to replace the Intermediate Fiber Tracker (IFT) by the Intermediate Silicon Layer (ISL). Main purpose of ISL was increased coverage for leptons and b tagging
The ISL full technical design report was written in three weeks.
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37. B tagging
50 % of b daughter tracks in top decays have pT  3 GeV
Mtop =175
Learned that b jets from top get tagged efficiently by finding displaced tracks below a few GeV
Seed vertexing allowed us to lower threshold to 500 MeV
But… SVX II had lots of material (front end electronics) on the innermost layer causing multiple scattering
low momentum tracks would be poorly resolved
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38. Material and Radius Material effect Add to this a pinch of:
depends on radius of innermost layer
Below about 2 cm, it starts not to matter
Add to this a pinch of:
UA2 experience with silicon on beam pipe and
CMS radiation hard detectors
and you get Layer 00
where a problem of too much material was fixed by adding more material?”
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39. IP Resolution*
A non-operating Layer 00 increases s by only ~1-2 mm at 1 GeV.
Building Layer 00 was a challenge: People, money, time, SPACE!
Managed to do it in 1 year with a group of ~10 people and ~750k$
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41. Silicon on the beam pipe
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42. The CDF II Si Tracker Layer
Inner/Outer Radii [cm]
Axial
Pitch [mm]
Stereo
Angle
1.35/1.62 25 - 1
2.5/3.0 60 90
141 2
4.1/4.6 62
125.5 3
6.5/7.0
1.2 4
8.2/8.7 5
10.1/10.6 65
6 Forward
19.7/20.2
112
6 Central
22.6/23.1
7 Forward
28.6/29.0
All silicon is p/n
All layers except Layer 0 are double-sided silicon
90 degree: Double Metal
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43. Run 2b
Began in 1999
Workshop led to a document detailing what needed to be done.
Replacement of SVXII+L00 was the only reasonable choice. ISL was probably ok…
Modular staves for simplicity and cost reduction
Single sided silicon (remember Yamamoto)
A new chip in ¼ micron technology, with all the bugs removed…
A lot less mass in the tracking volume
All technical challenges were met!
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44. Run IIB Layout Double sided staves: axial and stereo sensors
Uniform design for L2-6
L1 very similar to L2-6
L0 ~ L00 with only 2- chip sensors and supported by beam-pipe
Layer 0: 12 fold Axial
Layer 1: 6 fold Axial-90
Layer 2: 6 fold Axial-90
Layer 3: 12 fold Axial-90
Layer 4: 16 fold Axial-2.5
Layer 5: 20 fold Axial-2.5
Layer 6:24 fold Axial -90
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45. Silicon detectors and the search for the top
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46. The hunt for the top quark -1
Run 0 ( ) with 4.4 pb-1 collected:
- null results, so derived limits on the top quark mass:
- Mtop > 77 GeV (in 1991)
- Mtop > 91 GeV (in 1992)
The channels used included dileptons and lepton+jets events
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47. The hunt for the top quark -2
Run 1 (early years, ):
- taking advantage of the improved detector (silicon vertex above all) CDF starts to see some evidence with just 19 pb-1 by April 1994
2.8s effect based on 2 dilepton events and 10 lepton+jet events with b-tagging
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48. The first identified top event
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50. The hunt for the top quark -3
Run 1 (early years, ):
- in spite of the few events, CDF measured for this “evidence”:
- the production cross section (13.9 pb, ~1s higher)
- the top quark mass (174 GeV, quite good w.r.t. what we know now !)
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51. The hunt for the top quark -4
Run 1 ( ):
- in 1995 CDF (along with D0) claims the discovery, based on 67 pb-1 by April 1994
4.8s effect based on 6 dilepton events and 37 lepton+jet with b-tagging
Measured the tt production cross section pb and the top quark mass = GeV
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52. The hunt for the top quark -5
Run 1 ( ):
- the Padova group takes on the challenging task of searching the top production in the all-hadronic channel:
- need to develop a dedicated multijet trigger
- This is not enough: the QCD background is huge and the signal/background only about 1/1000
Years of thorough study of the kinematical characteristics of signal and background events
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54. The hunt for the top quark -5
Run 1 (1997):
Finally reached in 1997 for 109 pb-1 a reasonable signal/background
Measured the tt production cross section pb
Measured also the top quark mass = GeV
Values consistent with those found in the leptonic channels: a successful confirmation
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55. Precision measurements -1
Run 2 ( ):
- An upgraded detector with a better silicon vertex
Having established the existence of the top quark CDF moves towards the precise measurement of its properties
Measured the tt production cross section to a 5% precision. Consistency over all channels
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56. Precision measurements -2
Run 2 ( ):
Measured the top quark mass; average value with a x0.7% precision
Consistency over all channels
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57. Precision measurements -3
Run 2 ( ):
- In spite of the difficulties the all-hadronic channel, measured the top quark mass to be : right on with the world average
- The all-hadronic channel contributes with the second best weight to the CDF top quark mass measurement
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58. Conclusion
CDF silicon history has been a great success with many innovations and firsts!
Once questionable for a hadron collider, the CDF experience has helped to make silicon a mandatory requirement.
The paramount physics output of CDF heavily relies on the corageous choice to adopt in early times innovative detectors
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59. Aknowledgments
It is not easy to find documents of the Before Computer times.
Luckily Joe Incandela made a wonderful review in 2006 of the history of
silicon detectors in CDF. My talk deeply depends from this review.
I found the documents on the Tevatron early times in a Mel Shochet’s talk.
Many of the slides on the hunt for the top come from Andrea Castro, one
(lost for the wide public) from Luca Stanco.
I heartily thank all of them.
D. Bisello – Tevatron Day December 20th 2011