LHCb VErtex LOcator

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LHCb VErtex LOcator Displaced Vertex Trigger
Chris Parkes, CERN

• Vertex Detector
• Design
• Test Beam Results
• Displaced Vertex Trigger
• Algorithm
• Test Beam Emulation
• Conclusions
• Summary
• Future Plans

Beauty 99
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LHCb Detector
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Resolution

• Secondary Vertices
• B tagging
• Rejection of background
• Primary vertex resolution 40 ?m

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Geometry
Detectors separated 6cm during injection
small overlap
10cm
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Vertex Locator

• Detector Length 1m
• Station spacing varying
• from 4 - 12cm
• Phi Overlap of detectors
• Each Station has an R and
• a Phi measuring detector
• Stereo angle between
• successive Phi Detector layers

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Prototype Design
r-detectors
r-measuring detectors
?-measuring detectors
5 stereo tilt
Both detectors utilize a double metal layer to
readout inner strips whilst keeping electronics
outside active area.
?-detectors
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New Design

• 180 degree R Phi Detectors
• 2048 strips
• Smooth variation in pitch
• Ready in Autumn

• 16 chip Hybrid

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Mechanics
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Vacuum Vessel
RF shield vacuum barrier
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Radiation Environment

• Including effects of walls, vessel
• High doses at tips
• (1/r2)
• Detectors Irradiated
• Test-Beam September
• n on n Silicon as base solution

Dose after 1yr
1014
station 6
1 MeV equivalent neutrons/cm2
1013
1 2 3 4 5
6
cm
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Modelling

• Cooling Required
• Electric Field Distortions
• Radiation Response

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Software

• LHCb will use C
• BUT Technical Proposal work was in FORTRAN
• Test Beam
• used to gain experience with new language and
  Root
• All reconstruction software in C
• Cluster Making, Event Display, Track Fit,
  Alignment, Noise Studies...
• Software Designed for future use
• both useful code, and class design

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Trigger Levels
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Second Level Trigger Vertex Algorithm

• IDEA
• Separation of minimum bias events and B events
  by using the signature of displaced secondary
  vertices.
• AIM
• Minimum bias retention of less than 4 and a
  signal efficiency of more than 50.
• Boundary Conditions
• Input event rate of 1 MHz or 2Gbytes/second .
• Average execution time of about 250 microseconds.
• Implementation
• benchmark results show can be performed by 120
  1000 MIP processors

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Present Algorithm

• 2d
• Track finding using triplets of r-clusters
• track search starts in inner r sector
• Primary vertex reconstruction, x y z, by crossing
  tracks of opposite phi-sectors
• x y - resolution given by phi-sector
• Selection of tracks with large impact parameter
• Rejection of pile-up events

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Algorithm cont.

• 3d
• Add phi info. for large impact parameter tracks
• ambiguities resolved by stereo angle
• and impact parameter in xy-projection
• find two track combinations which are close
• calculate probability that one of the two tracks
  originate from the primary vertex
• based on impact parameter
• and geometry
• calculate total L1 probability by multiplying the
  individual probabilities

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Present Performance
2d and 3d track reconstruction efficiency of 98
and 95. Primary vertex resolution of 80micron
and 20micron for z and x/y.
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Test BeamSpring 98
12 Silicon Planes Slow Electronics
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Vertex Trigger Peformance

• Use Targets to simulate Primary Vertex
• Resolution
• Simulation 80?m
• Test Beam Extrapolated 80?m
• Assess sensitivity to detector misalignments

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Artificial B events

• Virtual B??? !
• Five events form one target
• minimum bias
• One From next target
• B event
• Good Performance

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Overviewof thereadoutscheme

• Analogue
• readout
• FE Rad. Hard
• gt2Mrad/yr
• FADC L1
• buffers 10m away
• Processing in
• DSPs after L1 accept

Front End Chip DMILL- SCTA or 0.25?m
CMOS- BEETLE
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LHC Speed Readout ChipTest-Beam Spring 99

• Aim
• Evaluate
• performance
• of detector
• equipped with
• SCT128A 40MHz
• FE chip
• Setup
• 6 plane Telescope
• 2 Test Detectors

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Test-Beam Results

• Clear Signal Observed
• Correlated with reference Telescope

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Time Response

• Rise Time 25ns
• Pulse Remaining after
• 25ns third of Signal
• 40 of LHCb events are
• preceded by an event
• simulation of B???
• Trigger efficiency
• drops above 30
• overspill
• SignalNoise 201

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Conclusions

• Prototype Detectors Tested ?
• New Design ?
• Displaced Vertex Trigger ?
• Future Work ..

So far the project is flying...
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Milestones

• 2000 Full Half station at 40MHz
• 2001 Technical design Report
• 2003 Construction
• 2004 Commissioning
• 2005 Start Data Taking

But there is still a long way to cycle..