Design and performance of the LHCb Silicon Tracker

1
Design and performance of the LHCb Silicon Tracker
Introduction Silicon Tracker project design
production Tracking strategy and
performance

• Kim Vervink
• Ecole Polytechnique Fédérale de Lausanne

TIME 05 - Zurich
2
A huge one arm spectrometer.
Dipole Magnet
Tracking Systems
Vertex Locator
Muon Chambers
Calorimeters
Rich 1 2
Precision measurements of CP violation and rare
decays in the B sector
3
Neighbouring detectors of the Silicon Tracker.
The vertex locator
R f detector strip orientation
21 stations around the interaction point
1m
The other subdetector that uses silicon
Half discs open during beam injection and close
around the interaction point up until 8 mm Whole
subdetector in vacuum Silicon thickness 300 mm
4
the outer tracker
Outer Tracker 3 stations with 4 double planes
4,7 m!
OT Straw tubes 5mm diameter Pitch 5,25 mm
Module production going to completion
5
Silicon Tracker Project
Some participants
Involved institutes M.I.P. Heidelberg
E.P.F.L. Lausanne U.S.C. Santiago de
Compostela UniZh Zurich
6
Challenges of the Silicon Tracker.

• Large areas have to be covered in Silicon. The
  Silicon design is adapted in order
• to keep it affordable
• not to become overloaded in readout channels
• ? Long readout strips
• Large distance between readout strips
• 2. Bunch crossings every 25ns
• ? fast shaping time
• 3. Momentum resolution is limited by multiple
  scattering
• ? minimization of material for the
  acceptance Thin sensors

• More load capacitance which increases the noise
• Beetle chip front-end design
• Adapted sensor thickness

Decreases S/N between strips ? optimise
width/pitch of the strips
Increases noise ? Optimised front-end electronics
Thinner sensors make S/N go down ? Best
compromise
7
Where is the Trigger Tracker?
Located behind the Velo Rich 1 Just in front
of the Magnet still in frindge field Active
area of the detector covers full acceptance
(cooling and electronics outside)
2 half stations in one box with in total 4
detector planes (0, 5, -5, 0 orientation)
8
Trigger Tracker
Staggered front-end readout hybrids
Silicon sensors
Pitch adaptor
Interconnect cable
Support rails
9
Where is the Inner Tracker?
Inner Tracker consists out of 3 stations,
surrounded by the Outer Tracker
2 boxes with 2 Si-sensors modules 2 boxes with 1
Si-sensor modules
TT
VELO
Complete IT detector inside the acceptance
(hybrids,pcbs, cooling, cabling, )
1,3 of acceptance, 20 of tracks.
10
Si-sensor
Pitch Adaptor hybrid with Beetles.
Kapton insulation
Aluminium Mini-Balcony

• Ladders are attached via the mini-balcony on a
  cooling rod, through which runs a cooling liquid
• detector is cooled (10C)
• in order to control the thermal runaway

Airex foam
Carbon Fiber support layer helps the cooling
flow to the sensors
Readout Cables, High and Low voltage cables
Cooling System
11
Silicon sensors for a fast and precise
measurement.
Bond pads DC readout!
HV input to the backside of the sensor
Left strip
Right strip
S/N value is above 12, taking into account the
charge loss between strips.
12
Production Status
Trigger Tracker 2 half stations with 280 (15
spare) readout sectors have to be build Inner
Tracker 3 stations with 336 (15 spare) modules
are to be produced and tested A typical
production trategy Building of a module using
jigs (parallel production)
Metrology Electrical test using internal test
pulses in order
to find broken or unbonded
strips Schedual Prototyping finished in
August for both detectors Start of
production All modules need to be
fabricated by April 2006
Installation in the LHCb pit in June 2006
Status Inner Tracker has about 20
modules produced Trigger Tracker
has 13 modules fabricated
Inner tracker testing box
13
A Trigger Tracker module and burn-in test setup
A built TT module
Cooling system
4 modules
Kapton readout cable
Burn-in box
Sensor
TT burn-in test
Hybrid
14
Support and IT modules are in theproduction
phase
The 2nd short ladder module that was made
Setup of the support frame
15
Silicon project essential part for the tracking
of the LHCb detector

• Reconstruction is not a trivial task
• LHCb gets about 50 primary particles per event
  check.
• 30 radiation length between interaction point
  and Rich2
• Secondary particles
• Multiple scattering
• Degrades the momentum resolution
• Interaction every 25 ns
• Spillover from previous bunch crossings

16
Tracking reconstruction
Particles spread out by magnet.
Bdl 4 Tesla m Warm magnet
Top view

• Multipass strategy
• Long tracks
• Ks after Velo
• Only Velo and TT

17
Tracking strategy

• First look for tracks that pass the whole
  tracking device (from Velo to T)
• Easiest to find
• Highest track resolution
• The most important ones for physics
  studies
• ? Start with a Velo Seed ( almost straight line
  only position and direction known)
• Adding one T station measurement to a Velo track
• Use optical parameterisation to calculate where
  the track passed using
• zCenter and dSlope
• Use the other measurements of the T stations to
  confirm hypothesis
• Fast algoritm main tracking done in HLT

Optical method parametrisation
zCenter
dSlope
18

• Second pass of long track reconstruction
• work backwards
• Seeding
• Seeding in T stations using unused hits
• Three hits define an almost straight line
• Collect more hits around trial track to confirm
  your hypothesis
• Also used to optimise Rich2 performance
• Tracking
• Transport the track seed to the Velo and compare
  with a Velo seed
• ? Look at the difference of track parameters
• Use c² criteria for matches
• This method adds about 3 to the overall long
  track finding efficiency

19
Other track types

• Of the remaining hits, make tracks from particles
  that passed only in TT and IT/OT
• Most are decay products of a Ks that
  decay outside VeLo
• Look for unused seeds in the T stations and add
  hits in TT
• Use optical method again.
• Look amongst the remaining particles for hits in
  the Velo and TT stations alone.
• Particles with low momentum bent
  out by magnetic field
• Look for unused Velo tracks with
  hits in the TT detector
• Moderate efficiency (70) and
  resolution (dp/p 15) but used to improve
  RICH 1 performance, kaon tagging and to find slow
  p from D

20
Tracking Performance on long tracks
Cut out in physics analysis
Momentum dependent B particles have higher
momentum Track finding efficiency
95
21
Performance on the resolution of the momentum and
the impact parameter (long tracks)
22
Summary

• The design and prototyping of the Silicon Tracker
  subdetectors is finished.
• Production of both the Silicon Tracker has
  started and
• Installation in the LHCb pit is schedualed in
  June 2006.
• Tracking performances are highly dependent on the
  quality of the Silicon Tracker detector.
• A tracking strategy has been implemented, and its
  performance is satisfactory.