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The CDF Online S ilicon V ertex T racker

The CDF Online S ilicon V ertex T racker. I. Fiori INFN & Universit y of Padova 7th International Conference on Advanced Technologies and Particle Physics Villa Olmo (Como) - October 15-19 2001. Outline. Tevatron and CDF upgrades for Run II The S ilicon V ertex T racker :

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The CDF Online S ilicon V ertex T racker

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  1. The CDF Online Silicon Vertex Tracker I. Fiori INFN & Universityof Padova 7th International Conference on Advanced Technologies and Particle Physics Villa Olmo (Como) - October 15-19 2001

  2. Outline • Tevatron and CDF upgrades for Run II • The SiliconVertexTracker : • - Physics motivation • - Working principle • - Architecture • - Track finding and fitting technique • SVT performance during summer 2001 Tevatron run • - various items … • Conclusions

  3. The Tevatron and CDF Upgrades for Run II Time Of Flight • New Tracking System • COT • L00 +SVXII + ISL • 3-D info • Extended tracking to forward region • New Trigger TIB = 396 (3636) - 132 (104 104)ns L = 1 - 2 * 1032 cm-2 s-1 ECM = 2.0 TeV

  4. CDF Trigger in run II • New for CDF run II at Level 1: • 2-D COT tracks available (XFT) • Fast SVXII readout (105 channels) : ~ 2.5 s detector elements CAL COT MUON SVX CES MUON PRIM. XCES XFT Track reconstruction with “offline” resolution at Level 2 XTRP SVT L1 CAL L1 TRACK L1 MUON d , Pt ,f d = 35 mm (at 2 GeV/c) GLOBAL L1 Fast !~10 ms (50 KHz L1 accept rate) SVT L2 CAL • 2-D tracks (drop SVXII stereo info) • Pt > 2 GeV/c • parallelized design : 12 -slices (30°each) • which reflects SVX II geometry GLOBAL LEVEL 2 TSI/CLK

  5. Why do we need the Silicon Vertex Tracker ? The Tevatron produces a lot of B events s = 50 mb ( ~ 10 events in Run II ) 11 bb But hidden in 1,000 more background s = 50 mb We need a Trigger pp “The New way” - SVT: trigger on displaced tracks “TheOldWay” - Trigger on leptonic B decays - SVX tracks used Offline to reconstruct Secondary Vertices Problems - Low B.R. for leptonic modes - Detector acceptance limited (Nonetheless, manyresultsfromCDF) B Primary Vertex B <d>100 m Secondary Vertex c450m ImprovedB physicscapabilities: fully hadronic B decays

  6. SVT: Silicon Vertex Tracker(Chicago-Geneva-Pisa-Roma-Trieste) SVT receives : • COT tracks from Level 1 XFT (,Pt) • Digitized pulse height in SVXII strips Performs tracking in a two-stage process: 1. Pattern recogniton: Search “candidate” tracks (ROADS) @ low resolution 2. Track fitting: Reassociate full resolution hits to roads and fits 2-D track parameters (d, , Pt ) using a linearized algorithm • SVX II geometry : • 12 -slices (30°each) “wedges” • 6 modules in z (“semi-barrels”) Reflected in SVT architecture

  7. The SVT Algorithm (Step I)Fast pattern Recognition Single Hit “XFT layer” • Hardware Implemented via the Associative Memory 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 (found roads) • Outputs the list of found roads • FAST! : pattern rec. is 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 Si Layer4 Road Si Layer3 Si Layer2 Si Layer1 SuperStrip (bin)

  8. The SVT Algorithm (Step II)Track Fitting When the track is confined to a road, fitting becomes easy ! : • Linear expansion of Parameters in the hit positions Xi : TRACK Pi = Fi * Xi + Qi ( Pi = pt , f , d , c1 , c2 , c3) Road boundary P0i X5 • … then refer them to the ROAD boundary : X05 XFT layer P0i + dPi = Fi * ( X0i + Xi ) + Qi X4 X04 SVX layer 4 P0i = Fi * X0i + Qi X03 X3 SVX layer 3 X2 X02 • Fi and P0 i coefficients are calculated in • advance (using detector geometry) and • stored in RAM SVX layer 2 X1 X01 SVX layer 1 • the task reduces to compute the scalar products (FPGA) : dPi = Fi * Xi SuperStrip 250 mm

  9. The SVT Boards AM Sequencer SuperStrip AM Board Hit Finder Hits Detector Data Matching Patterns Roads Roads + Corresponding Hits Hit Buffer L2 CPU Tracks + Corresponding Hits Track Fitter

  10. SVT racks

  11. SVT Performance (I)d -  correlation 28 Aug 2001 data, 2<40 no Pt cut • Sinusoidal shape is the effect of beam displacement from origin of nominal coordinates SVX only d = X0·sin () - Y0·cos () track (X0,Y0) d  X0 = 0.0153 cm Y0 = 0.3872 cm • Can find the beam consistently in all wedges even using only SVX

  12. Online fit of X-Y Beam position Run 128449 - October 6 2001 Can subtract beam offset online : I.P. with respect to beam position (online) : Independent fit on each SVXII z -barrel (6) d = 69 mm Beam is tilt is : dX/dZ  840 mrad dY/dZ  -500 mrad

  13. Understanding the width of d distribution d2 = B2 + res2 beam size i.p. resolution d ( mm ) • Present (online) 69 • Correct relative wedge misalignment 63 • Correct for d and  non-linearity 57 • Correct internal (detector layers) alignment 55 • Correct offline for beam z misalignment 48 • GOAL : SVXII + COT offline tracks (1wedge) 45 Can be implemented soon Need to have beam aligned

  14. Effect of non-linearity : • Because of the linear approximation done by Track Fitters, SVT measures : • dSVT d /cos (f) • fSVT  tan (f) • Becomes important for large beam offset • Can correct it making the online beam position routine fit a straight line on each wedge

  15. Expected SVT performance From SVT TDR (’96) : SVT simulation using RunI data Commissioning Run - Nov. 2000 : SVT simulation with SVX hits + COT Offline s ~ 45 mm s ~ 45 mm

  16. SVT Performance (II)correlation with offline tracks : SVT – COT Curvature : SVT - COT  = 2 mrad d : SVT - COT  = 0.33 ·10-4 cm-1  = 21mm

  17. Intrinsic transverse beam width Can extract B from the correlation between impact parameters of track pairs • If the beam spot is circular : <d1· d2> = B2· cos  B = 40 mm • But at present the beam is tilt (beam spot is an ellipsis) : short = 35 mm long = 42 mm

  18. Cut Online on chi2, Pt, d, N.tracks • L2 : • N. SVT tracks > 2 • | d | > 50 mm • 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 !

  19. Conclusions • 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 • Installation completed Autumn 2000 • Thoroughly tested on real Tevatron data April – September 2001 • Lots of tests and fine tuning done during the summer • Many things understood, will be implemented after the October -November Tevatron shutdown • Performance already close to design !

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