Transcript W combination for ‘98 winter conferences

The LHCb vertex detector
Frederic Teubert
CERN
EP division
VERTEX 99 (20-25) June
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
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p
D-p+
Vub



Vcb
Bs  DSK
Bd  DK
VERTEX 99 (20-25) June
Vtd
Vub


h
Vtd
Vts
 =l2h
Bs  J/yKS
J/yKL
Bs  J/yf
(Theoretically clean channels)
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. h ~ 1.9 to 4.9
-
 Has similar bb
acceptance to large
central detector
VERTEX 99 (20-25) June
Frederic Teubert
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LHCb detector
VERTEX 99 (20-25) June
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 Bpp/Kp).
 Vertex detector
 Need to reconstruct S.V. with good
resolution (IP  40m), for instance Bs
oscillations, and for trigger purposes.
 Trigger system
 bb / tot = 0.005
 Reduce the input rate from 40 MHz to
200 Hz.
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Frederic Teubert
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LHCb Trigger system
Level
Level 0
Characteristics
Sub-detector rates/latency
High Pt:
e
h

ECAL
HCAL
Muon detector
40 MHz
4 s
Interaction point
VELO
on-detector  off-detector electronics (1 TB/s)
Level 1
Large Impact Parameter
Secondary Vertices
VELO
High Pt
Tracker
1 MHz
256 s
off-detector  event buffer (2-4 GB/s)
Level 2
Refine secondary vertices VELO+Tracker
40 KHz
10 ms
Level 3
Partial reconstruction
5 kHz
200 ms
All
To tape = 200 Hz
VERTEX 99 (20-25) June
Frederic Teubert
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VELO: The LHCb vertex detector
VERTEX 99 (20-25) June
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 f measuring detector
• Stereo angle between
successive f detector layers
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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
vessel
Top
Half
window
primary vacuum
100cm
VERTEX 99 (20-25) June
Frederic Teubert
detectors
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Mechanical Support
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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)
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Frederic Teubert
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VELO baseline design
 The design of the vertex
detector is driven by:
 Fast track
reconstruction (L1
trigger)  rf geom.
 Radiation hard  rf
geom. + n on n
technology + operating
temperature 5C +thin
detector (depletion
voltage)
 Reduce multiple
scattering  150m thin
detectors
VERTEX 99 (20-25) June
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 50m
r-measuring
detectors
VERTEX 99 (20-25) June
Frederic Teubert
f-measuring
detectors
14
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
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
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Frederic Teubert
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Test Beam Setup
 6 r-sectors and 6 f-sectors (61) following closely the
baseline design, (300 m, n on n detectors, rf geometry, slow
readout VA2 chips).
 LHCb like events mimicked by arranging Cu-targets in front
of the silicon detectors.
VERTEX 99 (20-25) June
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
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
Frederic Teubert
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Primary vertex reconstruction
 Target thickness
300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 f implies,
PV  56 m
VERTEX 99 (20-25) June
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
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Frederic Teubert
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Results obtained in the lab with the SCTA chip
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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.
VERTEX 99 (20-25) June
25 ns
Frederic Teubert
25 ns
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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/N30 (in the LAB), S/N20 (in the TB)
 25 ns rising time, 1/3 of the signal after
25 ns.
VERTEX 99 (20-25) June
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
Frederic Teubert
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