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

How silicon detectors changed physics: the search for the top quark Outline CDF before Silicon SVX (1992-1993) SVX’ (1993-1996) SVXII and ISL Layer 00 Run 2b How silicon detectors changed physics: the search for the top quark D. Bisello – Tevatron Day December 20th 2011 2

Birth of the Tevatron & CDF before silicon D. Bisello – Tevatron Day December 20th 2011

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First silicons: SVX & SVX’ D. Bisello – Tevatron Day December 20th 2011

The Pisa Proposal D. Bisello – Tevatron Day December 20th 2011 10

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! D. Bisello – Tevatron Day December 20th 2011 11

P-775 This was the original collaboration. Look at this schedule! D. Bisello – Tevatron Day December 20th 2011 12

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. D. Bisello – Tevatron Day December 20th 2011 13

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. D. Bisello – Tevatron Day December 20th 2011 14

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 D. Bisello – Tevatron Day December 20th 2011 15

First recognition of Padova contribution Padova contributes to: test beam analysis, hybrids and chip test, sensor characterisation D. Bisello – Tevatron Day December 20th 2011

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The Ingredients of SVX’ AC coupled strips with FOXFET gate biasing D. Bisello – Tevatron Day December 20th 2011 19

Early indication of high efficiency, good resolution = 9 m D. Bisello – Tevatron Day December 20th 2011 20

Silicon and B tagging D. Bisello – Tevatron Day December 20th 2011 21

Early event displays IN BEAM COSMIC D. Bisello – Tevatron Day December 20th 2011 22

“Standalone” Si Tracking in SVX c. 1994 D. Bisello – Tevatron Day December 20th 2011 23

Radiation issues with the FOXFET bla D. Bisello – Tevatron Day December 20th 2011

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. D. Bisello – Tevatron Day December 20th 2011 25

CDF II: SVXII, ISL, Layer00, Run IIB D. Bisello – Tevatron Day December 20th 2011

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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 D. Bisello – Tevatron Day December 20th 2011 28

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. D. Bisello – Tevatron Day December 20th 2011 29 29

Radiation and technological issues D. Bisello – Tevatron Day December 20th 2011

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 D. Bisello – Tevatron Day December 20th 2011 31

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. D. Bisello – Tevatron Day December 20th 2011 32 32

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 ! D. Bisello – Tevatron Day December 20th 2011 33 33

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. D. Bisello – Tevatron Day December 20th 2011 34

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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 D. Bisello – Tevatron Day December 20th 2011 37

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?” D. Bisello – Tevatron Day December 20th 2011 38

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$ D. Bisello – Tevatron Day December 20th 2011 39

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Silicon on the beam pipe D. Bisello – Tevatron Day December 20th 2011 41

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 D. Bisello – Tevatron Day December 20th 2011 42

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! D. Bisello – Tevatron Day December 20th 2011 43

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 D. Bisello – Tevatron Day December 20th 2011 44 44

Silicon detectors and the search for the top D. Bisello – Tevatron Day December 20th 2011

The hunt for the top quark -1 Run 0 (1988-1989) 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 D. Bisello – Tevatron Day December 20th 2011

The hunt for the top quark -2 Run 1 (early years, 1992-1994): - 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 D. Bisello – Tevatron Day December 20th 2011

The first identified top event D. Bisello – Tevatron Day December 20th 2011 48

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The hunt for the top quark -3 Run 1 (early years, 1992-1994): - 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 !) D. Bisello – Tevatron Day December 20th 2011

The hunt for the top quark -4 Run 1 (1995-1997): - 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 6.8+3.6-2.4 pb and the top quark mass = 176+-13 GeV D. Bisello – Tevatron Day December 20th 2011

The hunt for the top quark -5 Run 1 (1992-1997): - 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 D. Bisello – Tevatron Day December 20th 2011

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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 10+-4 pb Measured also the top quark mass = 186+-16 GeV Values consistent with those found in the leptonic channels: a successful confirmation D. Bisello – Tevatron Day December 20th 2011

Precision measurements -1 Run 2 (1999-2011): - 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 D. Bisello – Tevatron Day December 20th 2011

Precision measurements -2 Run 2 (1999-2011): Measured the top quark mass; average value with a x0.7% precision Consistency over all channels D. Bisello – Tevatron Day December 20th 2011

Precision measurements -3 Run 2 (1999-2011): - In spite of the difficulties the all-hadronic channel, measured the top quark mass to be 172.5+-2.0: right on with the world average - The all-hadronic channel contributes with the second best weight to the CDF top quark mass measurement D. Bisello – Tevatron Day December 20th 2011

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 D. Bisello – Tevatron Day December 20th 2011 58

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