The CDF Silicon Vertex Trigger

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The CDF Silicon Vertex Trigger
SVT

• Vertex 2002
• Luciano Ristori
• Istituto Nazionale di Fisica Nucleare
• Pisa Italy

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SVT
The Silicon Vertex Trigger was designed and built
for the CDF collaboration by people from the
following institutions

• INFN Pisa
• INFN Trieste
• University of Chicago
• Université de Genève

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CDF DETECTOR
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CDF r-z view
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SVX II
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Why and how?

• Trigger on B hadronic decays
• B physics studies, eg. CP violation in B decays,
  Bs mixing
• new particle searches, eg. Higgs, Supersymmetry
• A b-trigger is particularly important at hadron
  colliders
• large B production cross section for B physics
• high energy available to produce new particles
  decaying to b quarks
• overwhelming QCD background
• need to improve S/B at trigger level
• Detect large impact parameter tracks from B
  decays using the fact that ?(B)?1.5 ps

Technical challenge!
secondary vertex
primary vertex
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SVT Silicon Vertex Trigger

• Inputs
• L1 tracks from XFT (?, pT)
• digitized pulse heights from SVX II
• Functionalities
• hit cluster finding
• pattern recognition
• track fitting
• Outputs
• reconstructed tracks (d, ?, pT)

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Triggering in Run 2

45 kHz
300Hz
60 Hz 20MB/s
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CDF Run II trigger architecture

• DØ results

• Tracking system
• central outer tracking (COT)
• silicon tracking (SVX II ISL)
• three-level trigger
• L1 5.5 ?s pipeline
• XFT L1 2D COT track
• L2 ?20 ?s processing time
• two stages of 10 ?s
• SVT at stage 1 of L2
• SVX II readout
• hit cluster finding
• pattern recognition
• track fitting

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Finding tracks in the silicon
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Building the Pattern Bank
In this example Straight lines, 5 layers, 12
bins/layer Total number
of patterns (12)2(5-1) 576
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AM chip internal structure
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AMchip
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Amplug mezzanine board
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AM Board
x16

• 128 Amchips
• x 128 patterns each
• 16K pattern board

VME
AMbus
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SVT basic architecture

• Pattern recognition and track fitting done
  separately and pipelined

Pattern recognition with Associative Memory
(AM) highly parallel algorithm using coarser
resolution to reduce memory size
Hits
Associative Memory
Hits
Hit Buffer
Roads
Track Fitter
Roads hits
Tracks (d, pT, ?)
Fast track fitting with linear approximation using
full resolution of the silicon vertex detector
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From non-linear to linear constraints
Non-linear geometrical constraint for a circle
F(x1 , x2 , x3 , ) 0
But for sufficiently small displacements
F(x1 , x2 , x3 , ) a0 a1Dx1 a2Dx2 a3Dx3
0
with constant ai
(first order expansion of F)
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Constraint surface
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SVT Wedges
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SVT system architecture
Hit Finders
raw data from SVX front end
Sequencer
Associative Memory
COT tracks
fromXTRP

roads
12 fibers
hits
Track Fitter to Level 2
Merger
hits
Hit Buffer
x 12 phi sectors
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SVT board count

• Hit Finders 42
• Mergers 16
• Sequencers 12
• AMboards 24
• Hit Buffers 12
• Track Fitters 12
• Spy Controls 8
• XTFA 1
• XTFB 2
• XTFC 6
• Ghostbuster 1

spares
TOTAL
136
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SVT board and crate layout
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Hit Buffer board
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Hit Finder board
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Merger board
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SVT crates in CDF counting room
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Impact parameter vs. phi
x
phi
d
y

• Raw

d
d
Subtracted
d y cos(phi) x sin(phi)
phi
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SVT beam profile
Impact parameter distribution
This distribution is interpreted as the
convolution of the actual transverse size of the
beam spot with the impact parameter resolution of
the SVT
sigma 50 um 43 um 25 um
SVT resolution
beam spot size
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Tevatron Beam Moves!
Beam center at beginning of store normally stable
within 20 microns. Drift during the duration of
a store of 20 to 30 microns in x,y (often
correlated) Beam slope more stable (variation lt20
microradians)
25 microns
TeV store 12 hours
x position (?m)
x slope (?rad)
y position (?m)
y slope (?rad)
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Hadronic B decays with SVT
Two paths
_at_ 3 x 1031 cm-2 s-1

• L1
• Two XFT tracks
• Pt gt 2.5 GeV Pt1 Pt2 gt 6.5 GeV
• ?? lt 135
• L2
• d0gt100 ?m for both tracks
• Validation of L1 cuts with ??gt20
• Lxy gt 200 ?m
• d0(B)lt140 ?m

• L1
• Two XFT tracks
• Pt gt 2.5 GeV Pt1 Pt2 gt 6.5 GeV
• ?? lt 135
• L2
• d0gt120 ?m for both tracks
• Validation of L1 cuts with ??gt2
• Lxy gt 200 ?m
• d0(B)lt140 ?m

3 KHz
5 Hz
Many body decays
Two body decays
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CDF as a Charm factory?
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Fully Hadronic B decays
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SUMMARY

• The design and construction of SVT was a
  significant step forward in the technology of
  fast track finding
• We use a massively parallel/pipelined
  architecture combined with some innovative
  techniques such as the associative memory and
  linearized track fitting
• SVT is now fully commissioned and we have shown
  we can handle all the technical challenges
  related to detector and beam alignment in real
  time
• Performance of SVT is as expected
• CDF is triggering on impact parameter and
  collecting data we hope will soon lead to
  significant physics results