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LHCb VErtex LOcator & Displaced Vertex Trigger
Chris Parkes, CERN LHCb VErtex LOcator & Displaced Vertex Trigger 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 Beauty ‘99
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Resolution Secondary Vertices B tagging Rejection of background
Primary vertex resolution 40 m Beauty ‘99
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Geometry series of discs Detectors separated 6cm during injection 10cm
small overlap 10cm Beauty ‘99
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Vertex Locator Detector Length 1m Station spacing varying
from cm Phi Overlap of detectors Each Station has an R and a Phi measuring detector Stereo angle between successive Phi Detector layers Beauty ‘99
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Prototype Design r-detectors r-measuring detectors -measuring
5 ° “stereo” tilt Both detectors utilize a double metal layer to readout inner strips whilst keeping electronics outside active area. -detectors Beauty ‘99
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New Design 180 degree R & Phi Detectors 2048 strips
Smooth variation in pitch Ready in Autumn 16 chip Hybrid Beauty ‘99
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Mechanics Beauty ‘99
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Vacuum Vessel RF shield vacuum barrier Top Half manipulators vessel
window Top Half primary vacuum vessel detectors 100cm RF shield vacuum barrier Beauty ‘99
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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 cm Beauty ‘99
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Modelling Cooling Required Electric Field Distortions
Radiation Response Beauty ‘99
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Software LHCb will use C++ Test Beam Software Designed for future use
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 Beauty ‘99
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Trigger Levels Beauty ‘99
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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 MIP processors Beauty ‘99
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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 z r Beauty ‘99
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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 Beauty ‘99
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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. Beauty ‘99
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Test Beam Spring ‘98 12 Silicon Planes Slow Electronics Beauty ‘99
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Vertex Trigger Peformance
Use Targets to simulate Primary Vertex Resolution Simulation 80m Test Beam Extrapolated 80m Assess sensitivity to detector misalignments Beauty ‘99
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Artificial B events Virtual B ! Good Performance
Five events form one target “minimum bias” One From next target B event Good Performance Beauty ‘99
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Overview of the readout scheme
Analogue readout FE Rad. Hard >2Mrad/yr FADC + L1 buffers 10m away Processing in DSPs after L1 accept Front End Chip DMILL- SCTA or 0.25m CMOS- BEETLE Beauty ‘99
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LHC Speed Readout Chip Test-Beam Spring ‘99
Aim Evaluate performance of detector equipped with SCT128A 40MHz FE chip Setup 6 plane Telescope + 2 Test Detectors Beauty ‘99
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Test-Beam Results Clear Signal Observed
Correlated with reference Telescope Beauty ‘99
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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 Signal:Noise ~ 20:1 Beauty ‘99
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Conclusions Prototype Detectors Tested New Design
Displaced Vertex Trigger Future Work ….. So far the project is flying... Beauty ‘99
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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….. Beauty ‘99
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