The LHCb VErtex LOcator
Doris Eckstein
Universität Hamburg, Institut für Experimentalphysik
DESY Seminar, 20 November 2007
The LHCb Experiment
- Motivation
The LHCb Detector
The VErtex LOcator
- Requirements
- Development and Tests
- Production and Installation
LHCb at the LHC
> 600 scientists
47 universities and laboratories
15 countries
Geneva
CERN
LHCb
ATLAS
CMS
ALICE
LHC Tunnel
20 November 2007
Doris Eckstein, DESY Seminar
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Slide from Malcolm John
Unitarity Triangle
1  2  8

VudVusVub  


2
4
 VcdVcsVcb       A2 5 ( 1 2    i )
1  2  8 (1  4 A2 )
V V V  
3
 A2  A4 ( 1 2    i )
 td ts tb   A (1    i )
2
VCKM
4
A3 (   i ) 


A2

2 4
1  A 2 
At LHCb terms up to 5 must be considered
* V
Vub
ud
Vcd Vcb
Vtd V*tb
a
(0,0)
(,)
(1-2/2)(,)
g
Vud V* td
Vcd V*cb
a
bc
gc
c
(0,1) (0,0)
*
Vub
Vtb
Vcd V*cb
*
Vcd Vcb
b
VudVub*  VcdVcb*  VtdVtb*  0
(1-22,2)
2
*
Vus
Vts
Vcd V*cb
VudVtd*  VusVts*  VubVtb*  0
Triangles almost identical, differences are at the per cent level
20 November 2007
Doris Eckstein, DESY Seminar
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Unitarity Triangle - 2007
Need significant constraint on g
Currently from direct measurements: 82o  20 o
Need Precision Measurement on g and further decrease errors on a and b
Bs mixing phase fs = 2c
20 November 2007
Doris Eckstein, DESY Seminar
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LCHb Physics goals
•
LHCb has a rich physics program and most analyses expect good results in the
early period (<2fb1):
– s(g)LHCb  5 degrees from Bs  Ds±K±, B0  DK etc
– s(fs)LHCb  0.02 radians
– Observation of Bs→mm
– Sensitivity to New Physics
phase in Bs → ff
•
In addition,
– s(Dms)
 0.012ps–1
– s(sin(2b))  0.02 (2x105/2fb–1)
[final B-factory result:
σ(sin(2b))  ± 0.017stat]
– s(a)
 10 degrees
– Charm physics
Expected constraints on Unitarity Triangle after5 years of LHCb data (10 fb-1)
if all measurements agree with the Standard Model
20 November 2007
Doris Eckstein, DESY Seminar
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The LHC Environment
•LHCb experiment to study CP violation in B-hadron decays
•At LHC: pp-collisions s =14TeV
•Bunch crossing frequency 40 MHz
•Pile-up at high luminosity
choose 2x1032 cm-2 s-1
most events have single interactions
Interactions/crossing
•Beams are locally less focused
Eases reconstruction (B-decay vertex)
Lower radiation level
 can come closer to beam
20 November 2007
Doris Eckstein, DESY Seminar
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LHCb – a forward Spectrometer
•full spectrum of B-hadrons produced
•B-cross-section large ~500μb
•1012 b-hadrons per nominal year [107s]
of data taking (2 fb-1)
B  , Bd0 , Bs0 , Bc , Λb ,....
~40% ~40% ~10%
~10%
b
b
bb correlated
Lorentz boost
b
b
Does not occur
LHCb: equippes the forward direction
15-250mrad acceptance
b
b
b
b
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The Detector
Vertex
Reconstruction
VELO
p
20 November 2007
Tracking system
VELO
Trigger Tracker
Inner/Outer Tracker
Particle ID
RICH1 and RICH2
Calorimeters
Muon system
Kinematics
Magnet + Trackers
Calorimeters
10 mrad
p
Doris Eckstein, DESY Seminar
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LHCb – at Point 8
Muon
20 November 2007
Calorimeters
RICH2
Trackers
RICH1
Magnet VELO
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Trigger
•Only ~1% of inelastic collisions produce b-quarks
•Branching fractions of interesting B decays are <10-4
10 MHz
visible
L0
High pt hadron, lepton, g
Flag multiple interactions, busy events
Hardware (custom boards), latency 4ms
Calo, Muon, Pileup, SPD
1 MHz full
Trigger Type
Physics
Use
200 Hz
Exclusive B
candidates
Specific final
states
600 Hz
High Mass dimuons
J/, bJ/X
300 Hz
D* Candidates
Charm,
calibrations
900 Hz
Inclusive b
(e.g. bm)
B data
mining
detector readout
HLT
Inclusive and exclusive selections
Software (PC farm 1800 nodes), complete event
Full information from detector
2 kHz
Output
rate
35 kB per event
VELO Information for fast reconstruction
 Fast data reduction
On tape
20 November 2007
Doris Eckstein, DESY Seminar
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VELO requirements
Measure proper time of B decay:
t = mB L / pc
Tracker:
tracking before magnet
cover full downstream detector acceptance
 21 stations allowing to measure
>=3hits/track
Number of hits per particle
 decay length L (~ 1 cm in LHCb)
 momentum p from decay products
(which have ~ 1–100 GeV)
Pseudorapidity
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VELO requirements
Vertex detector:
1m
•Reconstruct pp interaction vertex
< 10μm
wide spread of interaction region in z
many stations around z=0
Interaction Region, s5,3 cm
•Reconstruct B decay vertex
short track extrapolation distance and
minimal multiple scattering
IP < 40 μm
minimal material before first measured point
VELO sensors as close as possible to beam
7mm distance
 no beam pipe
20 November 2007
Doris Eckstein, DESY Seminar
Silicon
sensors
interaction
point
12
In the Vacuum
secondary Vacuum box
 sensors in detector vacuum 10-5 mbar
• Protect sensors against RF pickup
from LHC beam
• Protect the LHC Vacuum from possible
outgassing of detector modules
 RF boxes
•Injection: larger aperture required
 allow for retraction by 30mm
retractable
detector
halves
vacuum feedthroughs
Vacuum Vessel
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Doris Eckstein, DESY Seminar
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Radiation environment
an example Vdep
Vdep
•extremely inhomogeneous irradiation
dependence on R and station (z)
•5x1012 to 1.3x1014 neq/cm2/year
(compatible with other LHC detectors)
Middle
station
R/cm
Far
station
•Maintain a good S/N performance for at
least 3 years
•Extensive R&D program to select
sensor and optimize Front-End chip
•sensors: oxygenated n-on-n
•need cooling of detector modules
20 November 2007
Doris Eckstein, DESY Seminar
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n+-on-n strips
Routing lines
on 2nd metal layer
SiO2
n+ implants
p+ implant
resolution
p-on-n efficiency degrades fast
n-on-n efficiency ~100% for only 60%
depletion depth
n-on-n silicon, under-depleted:
•Limited loss in CCE
•Less resolution degradation
Depletion fraction
20 November 2007
Doris Eckstein, DESY Seminar
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Sensors
some more requirements:
•Fast 2D tracking and vertexing for Trigger
motivates R-and Φ-measuring sensors
•Optimize resolution + occupancy
pitch small at inner radii, larger at larger radii
•Single sided
•2048 channels per sensor
•2 x 2 x 21 sensors 172 k
channels
R measuring sensor
2nd metal layer Pitch adaptor
•40-102μm (R Sensor)
•36-97μm (Φ Sensor)
•sensitive area
from 8 to 42mm radius
•300μm thickness
RO chips
Φ-measuring sensor
©PPARC
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Module
Hybrid
•Double sided (R-sensor + Φ-sensor)
•Minimal material budget
•Kapton hybrids on Carbon fibre substrate
•0 CTE
•Cooled by CO2 cooling
•Precision of mounting for Trigger and Foil
•Metrology of Modules
Paddle
Cooling cookies
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Doris Eckstein, DESY Seminar
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Module Burnin
•
•
•
45 modules visually inspected – 483,000 bonds
36 modules fully burned in
14 step process including temp cycling, chip burnin, thermal images, vacuum
operation
20 November 2007
Doris Eckstein, DESY Seminar
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Assembly
•Electrical test to reveal problems
•Log fingerprint of each module
Insert modules
Connect cooling and cables
S/N
Take an empty half
Testpulse-S/N for all R-sensors
20 November 2007
Doris Eckstein, DESY Seminar
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The signal chain
60m cat6
2048 x 84 channels produce data
need online zero suppression
20 November 2007
TELL1 board
To PC farm
1MHz of data
Doris Eckstein, DESY Seminar
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Online zero suppression
ADC
10 bit
FIR correction
Pedestal correction/
Bit limit
8 bit
Reordering
LCMS
Clustering
7 bit
20 November 2007
•All on FPGAs
•Correct for cross talk and cable effects
•Take into account complex strip reordering
(non-consecutive strips on consecutive
readout channels)
•Implement algorithm for correction of
common mode
•Clustering  read out only cluster data
Data should serve a fast Trigger as well as sophisticated
offline reconstruction purposes
 Online cluster position calculated
 included in Cluster format as well as all cluster strip info
TELL1 Emulation for bit-perfect offline code development
cut tuning, etc.
Doris Eckstein, DESY Seminar
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Online zero suppression
Cluster Finding Efficiency
•Emulation developed and tested with testbeam and lab data
•Keep control about what happens online
TELL1 Algorithm Cluster Seeding Threshold
20 November 2007
Doris Eckstein, DESY Seminar
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Cross talk
•Cross talk varied between 5 and 20%
•analysis developed and FIR corrections extracted
•Implemented in alignment with dramatic improvement
in residual distributions
20 November 2007
Doris Eckstein, DESY Seminar
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VELO System Test – Testbeam Nov’06
x
y
z
20 November 2007
Doris Eckstein, DESY Seminar
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Noise and S/N
Common Mode Subtracted Noise of Each Run
4
Average Noise
HP1
HP2
HP3
HP4
3
2
1
R Detectors
Phi Detectors
0
11/10/06
Signal / Noise
11/12/06
11/14/06
11/16/06
11/18/06
11/20/06
Run Time
•
•
•
CM noise calculated in groups of 32 channels
Noise is stable throughout the data taking and is 1.9-2.6 ADC
counts for R sensors and 1.7-2.2 ADC counts for f sensors.
(1 ADC ~ 500 e-)
S/N ~ 23 for R, better for Φ
20 November 2007
Doris Eckstein, DESY Seminar
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Reconstructing the Vertex
•VELO retracted by 30mm during injection
•Moving: reconstruct beam position  move in
•Iterations
•Standard (fast) VELO tracking does not work
(R-Φ off centre)
•Special tracking developed
d = 5mm
d = 2mm
15 mm
Targets installed during testbeam
20 November 2007
Doris Eckstein, DESY Seminar
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Reconstructing the Vertex
•
Vertex reconstructed from
interaction between proton beam
(180 GeV) and sensors or targets.
Target
before alignment
…and after alignment
20 November 2007
Doris Eckstein, DESY Seminar
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Sensor Resolution
s40=8.4mm
s40=8.6mm
• Alignment at sophisticated level
– baseline cluster resolution can be extracted
– further improvements gained at large pitch by
eta corrections
20 November 2007
Doris Eckstein, DESY Seminar
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Simulated Event
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Doris Eckstein, DESY Seminar
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Detector Performance – Vertexing
Impact parameter resolution
dIP = 14mm+35mm/pT
•
•
proper time t=lm/p
Proper time resolution is dominated by
B vertex resolution
Bs→Dsp
•Impact parameter resolution
crucial for proper time resolution
•
~40 fs for most channels
20 November 2007
Doris Eckstein, DESY Seminar
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From Assembly to Installation
20 November 2007
Doris Eckstein, DESY Seminar
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Where it has to fit
What the beam sees
20 November 2007
Should be a perfect match
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VELO Installation
It was electrically tested
and it does work!
No damage occured during the
installation!
Now Commissioning.
20 November 2007
Doris Eckstein, DESY Seminar
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Summary
•LHCb is a dedicated B-Physics experiment at the LHC.
•The LHCb VELO is a crucial part of the detector and will contribute to reaching the
experiments physics goals.
•The VELO was recently installed and commissioning is ongoing.
•The commissioning in the
testbeam helped to
understand the
detector and to reach
the expected detector
performance.
Thanks to my former
VELO colleagues!
Good luck for the data
taking enjoy the exciting
time ahead!
20 November 2007
Doris Eckstein, DESY Seminar
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• BACKUP
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Tracking
cm
Outer Tracker
T1, T2, T3 made of
Outer Tracker and
Inner Tracker
Inner Tracker for
Region of high occupancy
cm
Trigger Tracker
•Measurement in fringe field of magnet
•Covers full detector acceptance
Provide pt for Trigger (together with VELO)
2*2 layers
Silicon microstrip sensors
500mm thickness
~200mm readout pitch
20 November 2007
Doris Eckstein, DESY Seminar
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Tracking
Tracking behind the Magnet – IT and OT
Inner Tracker:
•only 2% of area, but 20% of tracks
 Silicon microstrip sensors
•11 cm strips, ~200mm pitch
Outer Tracker:
•3 stations
•each made up of 4 double-layers of
Kapton/Al straw tubes
•glued together to form modules
two-sensor ladders:
410 mm thickness
Single sensors:
320 mm thickness
20 November 2007
Doris Eckstein, DESY Seminar
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g from Bs →Ds
u

V
K
s
V
c
 B
s
D
s
Slide from Malcolm John
K
Vcs
us
B
b
s s
•
b
s
Vcb*
s
u
s
D
K

+ ch.c. diagrams
Two tree decays (bc and bu), which interfere via Bs mixing:
– can determine (fs + g), hence g in a very clean way
Fit 4 tagged, time-dependent rates
– Extract fs + g, strong phase difference D, amplitude ratio
– Bs Dsp also used in the fit to constrain other parameters (w, Dms, Ds)
•
•
•
•
*
cb
c
Expect 6200 DsK
events in 2 fb–1
B/S < 0.5
•
•
Expect 140 000 Dsp
98% suppression achieved
with RICH PID system in
the analysis
•
•
Used to measure Dms
2 fb–1: s(Dms)  0.012ps–1
Study sensitivity by generating toy-experiments with experimental inputs derived from full
MC (Decay time and mass resolution, reconstruction efficiency, tagging…)
20 –
November
2007
Doris Eckstein, DESY Seminar
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Sensitivity
with 2 fb-1 : σ(g) ~ 13°
Slide from Malcolm John
Bs mixing phase: fs
0
s
b
Vtb*
t
B
•
•
•
•
•
s
Vts*
B
t
Vts
b
s
Vtb
b
0
s
B
0
s
Vcb
Vcs
s
c
c
s
s
J /
f
The equivalent of “sin2b“ for Bs mesons
In the standard model, fs is small: = -2arg(Vts)  0.0360.003
– Could be larger if New Physics is present in the box diagram
– Recent D0 result fs= –0.79 ±0.56(stat) +0.14–0.01(syst) with 1.1 fb–1
To resolve Bs oscillations, excellent proper time resolution is required
Modes sensitive to fs :
Bs→ J/ f
Bs→ c f
Bs→ J/ 
Bs→ Ds Ds
Control channel (Dms):
Bs→ Ds p
20 November 2007
Illustration of CPV:
toy-modeling LHCb data with fs
= 0.2 (i.e. 5SM)
events tagged as Bs
events tagged as Bs
Doris Eckstein, DESY Seminar
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Slide from Malcolm John
Bsmm expected sensitivity
LHCb limit on BR at 90% CL
LHCb sensitivity
(only bkg is observed)
(signal+bkg is observed)
Expected final CDF+D0 limit
Uncertainty in
bkg prediction
BF (x10–9)
•
Very exciting possibility of sensitivity to New Physics enhancement in the early period
Current upper limit from the Tevatron is around 20 x SM prediction
The dominate background is bm , bm.
– Background analysis is currently limited by Monte Carlo statistics (generation)
LHCb’s superior Bs invariant mass resolution is crucial in the background rejection
BF (x10–9)
•
•
•
5s observation
SM
3s evidence
SM
20 November 2007
“early
”
perio
d
Doris Eckstein, DESY Seminar
Integrated luminosity
(fb–1)
40
Noise (ADC cnts)
Noise
Φ
inner
R
outer
Total Noise
CM sub. Noise
inner strip
+ routingline
Increasing
Strip length
outer strip
20 November 2007
•Different noise levels understood,
primary reason strip geometry and routing
Doris Eckstein, DESY Seminar
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Detector Performance – Tracking
•tracks passing through full spectrometer:
e ~ 95%, a few percent of ghost tracks
•Momentum resolution Dp/p ~ 0.4%
VELO
TT
red = detected hits
blue = reconstructed tracks
T1 T2 T3
Mass resolution BsDsp
Typical sm~15 MeV
20 November 2007
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