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The LHCb Vertex detector
15/9/2003
• Physics– Goals– Properties and consequences
• LHCb– Overview of the detector
• Vertex– Specifications– Silicon stations– Overview– Details– Radiation hardness– Read-out chip developments
• Conclusions & ProspectsVertex2003, Sander Klous (on behalf of the LHCb
collaboration)
2
PhysicsGoals
Current status
• Investigate difference between Matter and Antimatter
• CP violation in standard model– Rotation between mass
eigenstates and weak eigenstates (CKM matrix)
– Expressed with Wolfenstein parameterization
• One of the 6 Unitary Triangles– Order or 2 for all sides
nWolfensteielementsCKM
AiA
A
iA
VVV
VVV
VVV
tbtstd
cbcscd
ubusud
1)1(
21
)(2
1
23
22
32
Accessible by LHCb
cdcb
tdtb
VV
VV*
*
0 1
Bs DsK
cdcb
udub
VV
VV*
*
Bs Ds
3
PhysicsProperties and consequences• You want B decays!
– B’s are heavy– Results from B – factories– LHCb offers
• Bs production• Higher yield
– Over constrained triangle
• LHC Production channel– Gluon fusion~ 1012 bb pairs a year– Boosted system (decay
length)
P
P
b
b
P
P b
b
Angular coverage• 15–300 mrad in bending plane• 15-250 mrad in non-bending plane
4
LHCbOverview of the experiment
Luminosity: 2 . 1032 cm-2s-1
5
Vertex detectorSpecifications
• Forward detector– Detectors only 8 mm from beam– 360º coverage in
• overlapping detectors• Low number of pp interactions per event
– In level-0 trigger (40 MHz)– Pile – Up detector
• Trigger on high pt displaced tracks– In level-1 trigger (1 MHz)– Standalone track reconstruction– Use stray field to select high pt
• Identify Bs oscillations– Vertex resolution:
17 m + 32m/pt 44 fs (Ds– 5 sensitivity to Bs oscillations with:
ms = 68 ps-1
• Tight material budget
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y
x
y
x
z
R
Vertex has standalone track and vertex reconstruction (Projection in
R-z plane)
Vertex detectorSilicon stations
45º segments
Second metallayer
42 mm8 mm
pitch from 40 to 103
m
Highest x-y resolution naturally
closest to interaction region
Stereo -20° and 10°
A
A
21 + 2
Thickness 220 mTemperature -5 ºCCO2 Cooling system
1meter
Pile - Upstations 250 mrad
15 mradAA
Interaction region = 5.3cm
Trigger:Talk on
Wednesday,Thomas
Schietinger
7
Vertex detectorOverview
Silicon stations in vacuum
Retractable detector halves
for beam injection
Thin exit foil
R detector
Phi detector
Beam
Detector onX-Y tables
8
Vertex detectorDetails
Bellows to accommodate
retractable detector halves
• 250 m thick• Complex shape (overlapping detectors)• Super plastic, hot gas formation
Thin separation between silicon
stations and beam
• Secondary vacuum• RF shield• Wakefield guide• Controlled pressure
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Middle station
Far station
Vertex detectorRadiation hardness
Radiation hardness• Replace detectors every 4 years
– Maximum irradiation per station5 x 1012 to 1.3 x 1014 neq/cm2/year
• Detector could have undepleted layer after irradiation– Resolution of p on n detector degrades fast
• Undepleted layer insulates strips from bulk– n on n ~100% efficient for only 60% depletion depth
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Beetle was selected in January 2003• Used in Vertex Detector and Silicon
Trackers• 0.25 m CMOS technology
– Intrinsically radiation hard– Single Event Upsets
– Triple redundant logic
• Analogue and digital output• Digital output used in level-0• Analogue output used in level-1
Read-out (Beetle)Introduction
x 186
x 128
Vpre
Ipre
Vsha
Isha IbufMux
to comparator (digital out)
In Out
Pipelinecells
Front-endsFront-end
Readout
Pipeline
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Read-out (Beetle)Analogue specifications
• 40 MHz clock frequency• 1 MHz read-out• Signal / Noise > 14• Rise time < 25 ns• Spill over < 30 %
Beetle1.1• Tested in SPS beam• 16 chips on 1 hybrid• PR02-R p-on-n detector
90%
10%
Rise time
Spill over
25 ns
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noise BaselineSignal
3 ns
3 ns
• Goal– Optimize performance– Check chip behavior
• 16 chips on 1 hybrid• Test beam environment
• Mimic LHCb operation– Sampling mode– Sampling rate
• Took 10 million events
Read-out (Beetle) Analysis
Peak
Spill over point
Convolution ofLandau and Gaussian
13
enc
(e- )
Detector bias =70 V Isha ( A) Ipre ( A) Vfs (mV) Events (M)1 Pulse shape scan, various settings and chips various 350 various 32 High statistics run on chips 0, 1, 2, 3, 4, 7 32 350 400 1
Detector bias =150 V3 Pulse shape scan, chips 8, 9, 10, 13, 14, 15 32 350 various 1,44 High statistics run, chips 8, 9, 10, 13, 14, 15 32 350 700 15 Confirmation runs, all chips 32 350 various 1,66 Single time sample run 32 350 700 17 High trigger rate run 32 350 700 1
Total 10
Read-out (Beetle)Results
Threshold = 14
Efficiency
Hits from previous
bunch crossing
Average capacitance: 10 pFSignal/Noise = 17.4 0.2Spill over = 36.1 % 1Rise time = 23.5 ns 0.5ENC = 500 + 50 e-/pF
Detector capacitance : 6 - 14 pFResulting S/N range: 14.5 -
21.5
14
Time1 2 3 4 5 6 70
Time sample
Continuous beam
Read-out (Beetle)Mimic sampling
mode/rateMimic sampling rate1. Occupy read-out circuit
• Send test pulses at high rate2. Mix with physics triggers3. Let ADC only read physics triggers
No deteriorating effects were found• Test beam mode: 19.7 0.2• Single time sample: 19.6 0.2
• Test beam mode: 18.7 0.2• High trigger rate: 18.7 0.2
Note: comparison with other settings
Time1 2 3 4 5 6 70
Time sample
Test beam mode
1
LHCb sampling mode
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Silicon and Read-outTo do
Beam test with irradiatedCzochralski silicon
To do:• Analysis of beam tests
– Irradiated Czochralski silicon– Single Beetle1.2 chip
• Beam test with new hybrid– 16 Beetle1.2 or 1.3 chips on
hybrid• Thinner detectors• 3D detectors ???
High resistance High oxygen content
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Conclusions
• LHCb is a next generation experiment for CP violation measurements• The vertex detector for LHCb is a mechanically challenging project
– Production has started• The silicon and hybrid developments are in their final phase
– Results from the beam test with irradiated Czochralski silicon are coming– The new hybrid will be tested in the test beam with 16 Beetle1.2 chips
• The Beetle read-out chip developments are in their final phase as well– Version 1.1 is extensively tested and complies almost with specifications– Version 1.2: a single chip is just tested in the test beam– Version 1.3 is the final version and is submitted on a MPW run in June
• Next year, system tests will start• The construction of the LHCb vertex detector is on track
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• Level-0 trigger combines– High pt info from calorimeters and muon
detectors– Pile - Up information from Pile – Up detector
• Counts number of primary vertices per event• 2 dedicated stations in the vertex detector• Digital read-out at 40 MHz• Outside acceptance
• Level-1 trigger– Identify displaced tracks at 1 MHz
• Low occupancy• High efficiency• R/Phi configuration
• Match with high pt tracks
Trigger:Talk on Thursday,
Thomas Schietinger
Vertex
Station: A B
ZA ZB
RARB
RA/RB = ZA/ZB = k
LHCbVertex and Trigger
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PhysicsProperties and consequences
• You want B decays!– B’s are heavy– Results from B – factories– LHCb offers
• Bs production• Higher yield
– Over constrained triangle
• LHC Production channel– Gluon fusion~ 1012 bb pairs a year– Boosted system
P
P
b
b
P
P b
b
20
LHCbSpecifications
• Angular coverage– 15–300 mrad in bending plane– 15-250 mrad in non-bending
plane• Trigger on displaced vertices• Excellent vertex resolution• Single pp interactions• Particle identification
– K/ separation– Flavor tagging– 1 – 150 GeV
For Bs decay is in the order of a few mm
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