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 15-19 2001

• 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

nsL = 1 - 2 1032 cm-2 s-1 ECM = 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 SVX CES

XFT XCESMUONPRIM.

XTRP

SVTL2

CAL

L1CAL

GLOBALL1

L1MUON

L1TRACK

GLOBALLEVEL 2

TSI/CLK

detector elements New for CDF run II at Level 1:

• 2-D COT tracks available (XFT)• Fast SVXII readout (105 channels) : ~ 2.5 s

Track reconstruction with “offline” resolutionat Level 2

SVTSVT

• 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 )

11bb

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

<d>100 m

c45

0m

B

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

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

• 32.000 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 ! :

Pi = Fi * Xi + Qi ( Pi = pt , , d )

P0i + Pi = Fi * ( X0i + Xi ) + Qi

P0i = Fi * X0i + Qi

Pi = Fi * Xi

• … then refer them to the ROAD boundary :

Road boundary

TRACK

P0i

X5XFT layer X05

SuperStrip 250 m

• the task reduces to compute the scalar products (FPGA) :

• Fi and P0 i coefficients are calculated in advance (using detector geometry) and stored in RAM

• Linear expansion of Parameters in the hit positions Xi :

SVX layer 4 X4 X04

SVX layer 3 X3 X03

SVX layer 2 X2 X02

SVX layer 1 X1 X01

The SVT Boards

Hit Finder

AM Sequencer AM Board

Hit Buffer

Track Fitter

Detector Data

Hits

SuperStrip

Matching

PatternsRoads

Roads + Corresponding

Hits

L2 CPU Tracks +

Corresponding Hits

SVT racks

Sinusoidal shape is the effect of beam displacement from origin of nominal coordinates

d = X0·sin () - Y0·cos ()

SVX only

(X0,Y0)

d

28 Aug 2001 data, 2<40 no Pt cut

Can find the beam consistently in all wedges even using only SVX

X0 = 0.0153 cmY0 = 0.3872 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 128449 - October 6 2001

d = 69 mBeam is tilt is : dX/dZ 840 raddY/dZ -500 rad

Online fit of X-Y Beam position

d2 = B

2 + res2

• 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

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 :• dSVT 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. 2000 : SVT simulation with SVX hits + COT Offline

From SVT TDR (’96) : SVT simulation using RunI data

~ 45 m

~ 45 m

Expected SVT performance

= 21m

= 0.33 ·10-4 cm

= 2 mrad

: SVT – COT

Curvature : SVT - COT

d : SVT - COT

SVT Performance (II)correlation with offline

tracks

<d1 · d2> = B2 · 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 tracksTrigger 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, Pt, 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