The LHCb VErtex LOcator
Olaf Behrendt
on behalf of the VELO group
Novosibirsk, 29.02.08
The LHCb VErtex LOcator INSTR08Olaf Behrendt
• LHC experiment dedicated to heavy flavour physics• CP-violation and rare decays of beauty and charm hadrons• constrain unitarity triangles and search for new physics
• forward spectrometer: 1.9 < < 4.9 [bb-pairs produced correlated in space]
• luminosity: 2 · 1032 cm-2s-1 [1012 bb-pairs per year]
Detector requirements:
• reconstruction in harsh radiation environment• selective trigger system [bb-production cross-section small]
• good vertex resolution [proper time]
• good particle identification [K/ separation]
The LHCb Experiment
Bs
Btag
K-
K+
+
+,K+
p p
PV
~1 cm
SV
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Role of the VELO in LHCb
Reconstruction Trigger
• precise tracking
• primary/secondaryvertices [lifetime]
• B-decay selection
• suppression of multiple interactions
• absoluteluminosity measurement
4 Tm
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Outline
• Design
• Module Production and Assembly
• Installation
• Control and DAQ
• Expected Performance
• Summary
• VELO alignment: see talk of M. Gersabeck
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Layout
• 2 retractable detector halves• 21 stations per half with an R and sensor• 2 Pile-Up stations per half [trigger]
injection
stablebeams
RF box
module
Pile-Up module
s
base
LHC vacuum
zx
y
x
y
6 cm
p
p partly overlappingsensors
IP
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Sensors
• divided into quadrants
• pitch: 40 - 100 m
• divided into short and long strip region
• pitch: 35 - 100 m
• stereo angle
r = 0.8 cm
r = 4.2 cm
2048strips
-sensor R-sensor
typ
e
invert
ed
not
typ
e in
vert
ed after 1 year of irradiation
[2 fb-1]
R [cm]
Udep [V]
n+ in n-bulk sensors [300 m]
• inherently radiation tolerant
• strip isolation via p-spray
• expected radiation dose:- 1.3 · 1014 neq/cm2/year at r = 0.8 cm- 5 · 1012 neq/cm2/year at r = 4.2 cm
after 3-4 years [~8 fb-1]: run partially depleted
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Modules
• double-sided hybrid to balance stresses due to “bi-metallic” effects
• typical non-planarities: 250 m
• sensor-sensor accuracy: < 10 m
• analogue front-end read-out:2 x 16 Beetle chips
• cooling: 2-phase CO2 [silicon @ -7° C]
carbon fibrepaddle
cooling block
carbonfibre
-sensor
R-side circuit
-side
circuit
R-sensor
thermal pyrolytic graphite
x
yz
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Module Production
receive and validate components
hybrid assembly
wire bonding on the hybrid
glue sensors on hybrid
wire bonding of sensors to hybrid
glue to carbon-fibre paddle
electrical check
module metrology
visual re-inspection
module burn-in- electrical test in vacuum- thermal stress- electronics burn-in
I/I (
%)
# module
good stability during burn-in
rejected
bonding failure rate:
• Backend: 0.000 %• Frontend: 0.010
%• Sensorend: 0.002
%
bad channels:
• R-sensors: 0.7 %-sensors: 0.5 %
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Fully Assembled VELO Half
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Vacuum System
LEFT DETECTOR BOX
• silicon detectors operated in vacuum
• RF shield of 300 m Al [3% Mg]
- constitutes beampipe in VELO region
- shape allows for overlapping sensors [alignment]
• avoid deformations:P = Pbeam - Pdetector < 10 mbar
• requirements beam vacuum: Pbeam = 10-8 mbar
• expected VELO vacuum:Pdetector < 10-4 mbar
This is what the LHC beams see …
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Installation
Lowering into the LHCb cavern …
… ready for installation …
… insertion of one half
October 2007:
• installation of both VELO halves
• transport and installation without any damage [IV curves]
installation rail
RF box
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Pumpdown [
mb
ar]
+2 mbar
-5 mbar
after 100 hoursdetector: 9 · 10-5 mbar
beam @ VELO: 2 · 10-9 mbar [without ion
pumps]
absolute pressure
differential pressure
The LHCb VErtex LOcator INSTR08Olaf Behrendt
DAQ and Control System
The LHCb VErtex LOcator INSTR08Olaf Behrendt
ARX
ARX
ARX
ARX GBE
TTCRx
CC
PC
• originally developed for the VELO, now used for (almost) all of LHCb
• analog input from 64 links• 10 bit analog to digital
conversion @ 40 MHz [A-Rx]• pre-processing FPGAs
[cross-talk, common mode, pedestals, clustering]
• data sent out via GigabitEthernet [GBE]
• max. L0 output rate: 1.1 MHz• control via credit-card
sized PC [CCPC]
Readout Board (TELL1)
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Commissioning
installation of cables and boards
Tests:
• ADC cards [A-Rx]
• Readout Boards [TELL1]
• Control Boards
• each readout slice– timing– cable check– noise level
Control and DAQ system (almost) completely commissioned
adjustment of timing to 0.65
nsproblematic A-Rx
card
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Testbeam
• 10 modules• 180 GeV beam
• small scale CO2 cooling system
• 6 modules readout simultaneously[full readout chain with final electronics boards]
• software: DAQ, ECS, tracking, vertexing, online monitoring
x = 0 mm, d = 2 mm
x = 15 mm, d = 5 mm
• data for 0, 4 and 8 degrees• interaction data
- 4 layers with 2 Pb targets [300 m]- test vertex reconstruction- emulate open and closed VELO
• > 50 million events to disk
November 2006
y
z
x
The LHCb VErtex LOcator INSTR08Olaf Behrendt
binaryresolution
linear fitto data
Testbeam Results
-sensors
R-sensors
• S/N: 20 - 24[decreases with r due to increasing strip length]
• resolution: 9 - 25 m [pitch: 40 - 100 m]
• S/N: 24 - 29
• resolution: 9 - 20 m [pitch: 35 - 100 m]
Landau Gaussian
active region
R-sensors
expected resolution improvements: cross-talk and corrections
R-sensors
full sensorsimulation
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Expected Tracking Performance
reconstructed track - hits in 3 stations
LHCb acceptance: 1.9 < <
4.9
= -ln tan(/2)
For typical B decay modes:
• primary vertex resolution:- x,y: ~10 m, z: ~60 m
• proper time res.: ~40 fs• B mass res.: 12 - 25 MeV
B decays
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Status
• module production and burn-in: completed March 2007
• module assembly on detector halves: completed March 2007
• vacuum/detector positioning system: installed
• installation of detector halves:October 2007
• cooling system: installed
• HV-/LV-system: installed
• Electronic boards/cables: installed
• system checkout: ongoing
• system test foreseen within the next two months
CO2 cooling system
positioning system
LV system
The LHCb VErtex LOcator INSTR08Olaf Behrendt
• VErtex LOcator is small but complex detector
• precision tracking very close to the interaction region
• radiation tolerant design
• results from the testbeam in November 2006
– S/N: 24 - 29 (), 20 - 24 (R)
– resolution: 9 - 20 m (), 9 - 25 m (R)
• on schedule for first beams in 2008
Summary
Backup Slides
The LHCb VErtex LOcator INSTR08Olaf Behrendt
Luminosity Measurement
10-7 mbar Xe1011 p/bunch
30
Hz
per
bu
nch
Method:
• injection of a tiny bit of gas into VELO region
• reconstruction of beam-gas interaction vertices- beam angles, profiles & relative positions- calculate luminosity
• simultaneous reconstruction of beam-beam interaction vertices- calibrate ‘reference’ cross-section
test setup for gas injection
• expected beam size: x ≈ y ≈ 70 m
• expected vertex resolution: pv ≈ 30 m
expected accuracy: ~1%
LHCbmachine
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