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

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 Outline

       ns L =  cm -2 s -1 E CM = 2.0 TeV New Tracking System COT L00 +SVXII + ISL 3-D info Extended tracking to forward region New Trigger Time Of Flight The Tevatron and CDF Upgrades for Run II

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

Why do we need the Silicon Vertex Tracker ? The Tevatron produces a lot of B events   b ( ~ 10 events in Run II ) 11 bb But hidden in 1,000 more background   mb pp We need a Trigger “The Old Way” - Trigger on leptonic B decays - SVX tracks used Offline to reconstruct Secondary Vertices Problems - Low B.R. for leptonic modes - Detector acceptance limited (Nonetheless, many results from CDF) “The New way” - SVT: trigger on displaced tracks Improved B physics capabilities: fully hadronic B decays B Primary Vertex Secondary Vertex  100  m c  450  m B

SVT: Silicon Vertex Tracker (Chicago-Geneva-Pisa-Roma-Trieste) SVT receives : COT tracks from Level 1 XFT ( ,P t ) Digitized pulse height in SVXII strips Performs tracking in a two-stage process: 1. Pattern recogniton: Search “candidate” tracks low resolution 2. Track fitting: Reassociate full resolution hits to roads and fits 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

Road The SVT Algorithm (Step I) Fast pattern Recognition 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 roads for each 30 ° slice ~250 micron SuperStrips > 95% coverage for Pt >2 GeV Single Hit SuperStrip (bin) “XFT layer” Si Layer1 Si Layer2 Si Layer3 Si Layer4

The SVT Algorithm (Step II) Track Fitting When the track is confined to a road, fitting becomes easy ! : 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 X5X5 XFT layer X 05 SuperStrip 250  m the task reduces to compute the scalar products (FPGA) : F i and P 0 i coefficients are calculated in advance (using detector geometry) and stored in RAM Linear expansion of Parameters in the hit positions X i : SVX layer 4 X4X4 X 04 SVX layer 3 X3X3 X 03 SVX layer 2 X2X2 X 02 SVX layer 1 X1X1 X 01

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

SVT racks

 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 = cm Y 0 = cm track SVT Performance (I) d -  correlation

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

 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

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 :

Commissioning Run - Nov : SVT simulation with SVX hits + COT Offline From SVT TDR (’96) : SVT simulation using RunI data  ~ 45  m Expected SVT performance

 = 21  m  = 0.33 ·10 -4 cm   = 2 mrad  : SVT – COT Curvature : SVT - COT d : SVT - COT SVT Performance (II) correlation with offline tracks

=  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

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

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 ! Conclusions