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S. Donati University and INFN Pisa 9th Topical Seminar on Innovative Particle and Radiation Detectors, May 23-26 2004, Siena, Italy The CDF Online Silicon Vertex Tracker
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Overview of the CDF-II detector and trigger The Online Silicon Vertex Tracker : - Physics motivation - Working principle - Architecture - Track finding and fitting technique SVT performance in the early phase of CDF Run II SVT upgrades Conclusions Outline
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Time Of Flight The CDF-II Detector and Trigger CAL COT MUON SVXCES XFT XCES MUON PRIM. XTRP SVT L2 CAL L1 CAL GLOBAL L1 MUON L1 TRACK GLOBAL LEVEL 2 TSI/CLK detector elements 2-D COT tracks available @Level 1 (XFT) Fast SVXII readout (10 5 channels) ~10 s SVT: 2D tracks in silicon (drops stereo info) SVT: d = 35 mm (at 2 GeV/c) Parallel design (12 slices in phi) reflects SVXII design
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Why do we need the Silicon Vertex Tracker ? Extract the huge Tevatron beauty/charm production ( = 50 b) from the 1,000 larger QCD background ( = 50 mb) at trigger level bb pp Primary Vertex Secondary Vertex d = impact parameter (~100 m) B Decay Length Lxy L xy 450 m P T (B) 5 GeV In the pre-SVT age CDF was limited to leptonic modes (B J/ X, B lDX, suffering from low BR and acceptance) Two Track Trigger Pt(trk) > 2 GeV IP(trk) > 100 m Fully hadronic modes: 2-body charmless B decays, B S mixing, Charm. Displaced Track + Lepton (e, ) Pt(lepton) > 4 GeV (was 8 GeV) IP(trk) > 120 m Semileptonic modes: high statistics b-hadron lifetimes, b tagging, b mixing
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SVT: Silicon Vertex Tracker (Chicago-Geneva-Pisa-Roma-Trieste) SVT receives: -COT tracks from Level 1 ( ,P t ) -Digitized pulse height in SVX strips and performs tracking in a two-stage process: 1. Pattern recogniton: Search “candidate” tracks (ROADS) @low resolution. 2. Track fitting: Associate full resolution hits to roads and fit 2-D track parameters (d, ,P t ) using a linearized algorithm. SVX II geometry: 12 -slices (30°each) “wedges” 6 modules in z (“semi-barrels”) Reflected in SVT architecture
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The SVT Algorithm (Step I) Fast Pattern Recognition Road Hardware Implemented by AM chip (full custom - INFN Pisa) : - Receives the list of hit coordinates - Compares each hit with all the Candidate Roads in memory in parallel - Selects Roads with at least 1 hit in each SuperStrip - Outputs the list of found roads FAST: pattern rec. complete as soon as the last hit of the event is read - 32.000 roads for each 30 ° slice - ~250 micron SuperStrips - > 95% coverage for Pt >2 GeV Single Hit SuperStrip (bin) “XFT layer” Si Layer 1 Si Layer 2 Si Layer 3 Si Layer 4
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The SVT Algorithm (Step II) Track Fitting When the track is confined to a road, fitting becomes easier P i = F i X i + Q i ( P i = p t, , d ) P 0i + P i = F i ( X 0i + X i ) + Q i P 0i = F i X 0i + Q i P i = F i X i then refer them to the ROAD boundary Road boundary TRACK P 0i X5X5 XFT layer X 05 SuperStrip 250 m the task is to compute simple scalar products F i and P 0 i coefficients are calculated in advance (using detector geometry) and stored in a RAM Linear expansion of parameters in hit positions X i SVX layer 4 X4X4 X 04 SVX layer 3 X3X3 X 03 SVX layer 2 X2X2 X 02 SVX layer 1 X1X1 X 01
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The SVT Boards Hit Finder AM Sequencer AM Board Hit Buffer Track Fitter SVXII Data COT tracks from Level 1 Super Strip Matching Patterns Roads Roads + Corresponding Hits L2 CPU Tracks + Corresponding Hits
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Sinusoidal shape is the effect of beam displacement from origin of nominal coordinates d = X 0 ·sin ( ) - Y 0 ·cos ( ) SVX only (X 0,Y 0 ) d 28 Aug 2001 data, 2 <40 no Pt cut Can find the beam consistently in all wedges even using only SVX X 0 = 0.0153 cm Y 0 = 0.3872 cm track SVT Performance (I) d - correlation
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I.P. with respect to beam position (online) : Independent fit on each SVXII z -barrel (6) Can subtract beam offset online : Run 128449 - October 6 2001 Online fit of X-Y Beam position ~ 45 m
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Highlights of B physics (hadronic channels) B 0 s D - s + golden channel to resolve B 0 s fast oscillations B 0 s D - s + Bh+h'-Bh+h'- B h + h' - crucial to understand CP violation in the B sector (CDF-II competitive and complementary to B factories)
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Highlights of B physics (semileptonic channels) B+l+D0XB+l+D0X 1400 Bs l D s l[ ] High statistics semileptonic B samples are excellent for calibration, B + /B 0 and Bs/B 0 lifetime measurements,tagging and B 0 and Bs mixing (for moderate x s )
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Why is the SVT upgrade important ? 4/4 – 4/5 1.looser matching criteria 2.Ghost roads 3.5 layers larger Patterns 27 sec Time ( s) 5/5 4/5 This road share all hits with the 5/5. It’s a ghost. More memory for thinner patterns 4 LVL2 buffers dead time depends on: total LVL2 latency fluctuations Empty SS
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First step: new Associative Memory System Use standard cell chips to perform AM chip function Increase from 128 pattern/chip 4k pattern/chip (thinner roads, less fits, faster system, can cope with increasing Tevatron luminosity, increase coverage to forward region, lower pt threshold)
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SVT performs fast and accurate 2-D track reconstruction (is part of L2 trigger of CDF-II). Tracking is performed in two stages: - pattern recognition - high precision track fitting Taking good data since the beginning of CDF Run II, many analyses in the field of beauty/charm physics only possible thanks to this device Upgrade of the system in progress to cope with increasing Tevatron luminosity Conclusions
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CAL COT MUON SVXCES XFT XCES MUON PRIM. XTRP SVT L2 CAL L1 CAL GLOBAL L1 MUON L1 TRACK GLOBAL LEVEL 2 TSI/CLK detector elements New for CDF run II at Level 1: 2-D COT tracks available (XFT) Fast SVXII readout (10 5 channels) : ~ 2.5 s Track reconstruction with “offline” resolution at Level 2 SVT 2-D tracks (drop SVXII stereo info) Pt > 2 GeV/c parallelized design : 12 -slices (30°each) which reflects SVX II geometry Fast ! ~10 s (50 KHz L1 accept rate) d = 35 m (at 2 GeV/c) d, Pt, CDF Trigger in run II
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Accurate deadtime model (ModSim) 7% M. Schmidt 4/5 sept. 2003 Ini_lum=44*10 30 4/5 simulation Ini_lum=10*10 30 4/4 4/5+SVTupgrade+L2upgr Simulation: Ini_lum ~ 20*10 30 Low lum, Run IIa L2, no COT prob. To be done again.
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d 2 = B 2 + res 2 Present (online)69 Correct relative wedge misalignment63 Correct for d and non-linearity 57 Correct internal (detector layers) alignment55 Correct offline for beam z misalignment 48 GOAL : SVXII + COT offline tracks (1wedge)45 beam size i.p. resolution d ( m ) Can be implemented soon Need to have beam aligned Understanding the width of d distribution
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Because of the linear approximation done by Track Fitters, SVT measures : d SVT d /cos ( ) SVT tan ( ) Becomes important for large beam offset Can correct it making the online beam position routine fit a straight line on each wedge Effect of non-linearity :
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Commissioning Run - Nov. 2000 : SVT simulation with SVX hits + COT Offline From SVT TDR (’96) : SVT simulation using RunI data ~ 45 m Expected SVT performance
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= 21 m = 0.33 ·10 -4 cm = 2 mrad : SVT – COT Curvature : SVT - COT d : SVT - COT SVT Performance (II) correlation with offline tracks
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= B 2 · cos Can extract B from the correlation between impact parameters of track pairs If the beam spot is circular : B = 40 m But at present the beam is tilt (beam spot is an ellipsis) : short = 35 m long = 42 m Intrinsic transverse beam width
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L2 : N. SVT tracks > 2 | d | > 50 m 2 < 25 Pt > 2 GeV/c L1 prerequisite : 2 XFT tracks Trigger selection successfully implemented ! About 200 nb -1 of data collected with this trigger where we can start looking for B’s ! Cut Online on chi2, P t, d, N.tracks
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SVT racks
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