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The LHCb vertex detector
Frederic Teubert CERN EP division VERTEX 99 (20-25) June 1999 Frederic Teubert
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What do we want to measure?
The main goal is the determination of the origin of CP violation, by precision measurements in many B decay modes. The possibility of measuring several of the CP parameters in a single experiment, could give a glimpse on new physics beyond the SM. VERTEX 99 (20-25) June 1999 Frederic Teubert
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What do we want to measure?
Vtd Vtb*+ Vcd Vcb*+ Vud Vub*= 0 Vtd Vud*+ Vts Vus*+ Vtb Vub*= 0 Bd p+p- rp D*-p+ Vub Vtd Vtd Vub Vts Vcb = l2h Bs DSK Bd DK* Bs J/yKS J/yKL Bs J/yf (Theoretically clean channels) VERTEX 99 (20-25) June 1999 Frederic Teubert
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LHC environment - - - Large bb cross section (~500 b), with
L = 2·1032 cm-2 s-1 1012 bb pairs per year. Energy of the B’s ~80 GeV ~7 mm. A single-arm spectrometer covering min ~ 15 mrad (beam pipe and radiation) max ~ 300 mrad (cost) i.e. ~ 1.9 to 4.9 Has similar bb acceptance to large central detector - - VERTEX 99 (20-25) June 1999 Frederic Teubert
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LHCb detector VERTEX 99 (20-25) June 1999 Frederic Teubert
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Critical LHCb detectors
RICH detectors Two detectors covering the range between 1 and 150 GeV. Needed for particle ID (for instance Bpp/Kp). Vertex detector Need to reconstruct S.V. with good resolution (IP 40m), for instance Bs oscillations, and for trigger purposes. Trigger system bb / tot = 0.005 Reduce the input rate from 40 MHz to 200 Hz. VERTEX 99 (20-25) June 1999 Frederic Teubert
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LHCb Trigger system Level Characteristics Sub-detector rates/latency
Level High Pt: e ECAL MHz h HCAL s Muon detector Interaction point VELO on-detector off-detector electronics (1 TB/s) Level Large Impact Parameter MHz Secondary Vertices VELO s High Pt Tracker off-detector event buffer (2-4 GB/s) Level Refine secondary vertices VELO+Tracker KHz 10 ms Level Partial reconstruction All kHz 200 ms To tape = 200 Hz VERTEX 99 (20-25) June 1999 Frederic Teubert
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VELO: The LHCb vertex detector
VERTEX 99 (20-25) June 1999 Frederic Teubert
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VELO: The LHCb vertex detector
Small overlap 6 cm during injection 12 cm Detector length 1m Closest distance to the beam axis 1 cm. Station spacing varying from 4-12cm Each station has an r and a measuring detector Stereo angle between successive detector layers VERTEX 99 (20-25) June 1999 Frederic Teubert
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Vacuum vessel The design of the vacuum tank and support structures of VELO needs to satisfy several requirements: Low mass in the acceptance region Provide alignment and retractability of VELO Mechanical stresses induced by heat loading Maintain high-vacuum compatibility while providing signal feed-through (22000 signal wires 50 twisted-pairs per hybrid) manipulators window Top Half primary vacuum vessel detectors 100cm VERTEX 99 (20-25) June 1999 Frederic Teubert
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Mechanical Support VERTEX 99 (20-25) June 1999 Frederic Teubert
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RF shield primary secondary Vacuum
2*100 micron / detector station Need wake field suppressor Best case: 100 micron once Worst case: 2.4*100 micron/detector station for low angle tracks (but high p) VERTEX 99 (20-25) June 1999 Frederic Teubert
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VELO baseline design The design of the vertex detector is driven by:
Fast track reconstruction (L1 trigger) r geom. Radiation hard r geom. + n on n technology + operating temperature 5C +thin detector (depletion voltage) Reduce multiple scattering 150m thin detectors VERTEX 99 (20-25) June 1999 Frederic Teubert
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Routing of channels Both detectors utilize a double metal layer to readout inner strips. Detectors fabricated on 100mm wafer inner radius 10mm readout tracks spaced 50m r-measuring detectors -measuring detectors VERTEX 99 (20-25) June 1999 Frederic Teubert
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Irradiation The particle fluence is dominated by primary particles.
The maximum equivalent dose of 1MeV neutrons per station in one year is 1014/cm2 The idea is to replace the innermost detectors each year. VERTEX 99 (20-25) June 1999 Frederic Teubert
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Overview of the Readout scheme
Analogue readout FE Radiation Hard FADC + L1 buffers 10m away Processing in DSPs after L1 accept VERTEX 99 (20-25) June 1999 Frederic Teubert
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Test Beam Setup 6 r-sectors and 6 -sectors (61) following closely the baseline design, (300 m, n on n detectors, r geometry, slow readout VA2 chips). LHCb like events mimicked by arranging Cu-targets in front of the silicon detectors. VERTEX 99 (20-25) June 1999 Frederic Teubert
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Alignment and cluster resolution
The alignment of the detectors is an important issue for the trigger performance. No possibility to use the alignment constants for tracks in the rz plane. The position of the detector needs to be known with a precision of few 10 m. The alignment constants measured with the POLI machine (3D survey machine) and minimizing the 2 of the fitted tracks agree better than 50 m. We expect to be able to install the detectors with a precision better than 10 m. VERTEX 99 (20-25) June 1999 Frederic Teubert
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Alignment and cluster resolution
By measuring the residuals we determine a cluster resolution of = 6 m VERTEX 99 (20-25) June 1999 Frederic Teubert
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Primary vertex reconstruction
Target thickness m Distance to the first silicon detector 7.5 cm Extrapolating this results to the statistics of an LHC event and full angular coverage in implies, PV 56 m VERTEX 99 (20-25) June 1999 Frederic Teubert
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First Test with a Fast Readout Chip (SCTA 128)
One r-detector equipped with 4 SCTA/hybrid Main goal: Noise Study Over Spill Clock 40 MHz VERTEX 99 (20-25) June 1999 Frederic Teubert
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Results obtained in the lab with the SCTA chip
VERTEX 99 (20-25) June 1999 Frederic Teubert
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Results obtained in the Test Beam with the SCTA chip
S/N 20 Rising time 25 ns After 25 ns the signal is reduced to 1/3 of the maximum. 25 ns 25 ns VERTEX 99 (20-25) June 1999 Frederic Teubert
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Outlook First prototype of the VELO detector in a test-beam shows reasonable performance Cluster resolution 6 m Alignment studies, Level 1 studies LHCb like events mimicked by arranging Cu-targets in front of the Si Equivalent LHCb resolution pv 56 m Test of fast electronics (SCTA 128) S/N30 (in the LAB), S/N20 (in the TB) 25 ns rising time, 1/3 of the signal after 25 ns. VERTEX 99 (20-25) June 1999 Frederic Teubert
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Future plans Test of irradiated n on n detectors with fast electronics in the TB (August ‘99) Test of p on n technology (smaller pitches) in the TB. Come to a conclusion about the best technology at the end of ‘99 Detector optimization (2 modules of 182 with 45.5 sectors, reduce inner radius to 8 mm and reduce outer radius to fit in one wafer). Test (SCTA or BEETLE) + ODE in the TB by summer ‘00. Come to a conclusion by the end of ‘00 VERTEX 99 (20-25) June 1999 Frederic Teubert
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