the lhcb vertex locator doris eckstein universität hamburg, institut für experimentalphysik the...
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The LHCb VErtex LOcator
Doris EcksteinUniversität Hamburg, Institut für Experimentalphysik
The LHCb Experiment - MotivationThe LHCb Detector The VErtex LOcator - Requirements - Development and Tests - Production and Installation
DESY Seminar, 20 November 2007
20 November 2007 Doris Eckstein, DESY Seminar 2
LHCb
ATLAS
ALICECMS
LHC Tunnel
Geneva
CERN
> 600 scientists47 universities and laboratories 15 countries
LHCb at the LHC
20 November 2007 Doris Eckstein, DESY Seminar 3
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At LHCb terms up to 5 must be considered
Triangles almost identical, differences are at the per cent level
Unitarity TriangleSlide from Malcolm John
20 November 2007 Doris Eckstein, DESY Seminar 4
Unitarity Triangle - 2007
Need significant constraint on
Need Precision Measurement on and further decrease errors on and
Bs mixing phase s = 2
oo 2082 Currently from direct measurements:
20 November 2007 Doris Eckstein, DESY Seminar 5
• LHCb has a rich physics program and most analyses expect good results in the early period (<2fb1):– ()LHCb 5 degrees from Bs Ds
±K±, B0 DK etc
– (s)LHCb 0.02 radians– Observation of Bs→– Sensitivity to New Physics
phase in Bs →
• In addition, (ms) 0.012ps–1 (sin(2)) 0.02 (2x105/2fb–1) [final B-factory result:
σ(sin(2)) ± 0.017stat] () 10 degrees– Charm physics
LCHb Physics goals
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 6
•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
•Beams are locally less focusedEases reconstruction (B-decay vertex)Lower radiation level can come closer to beam
Interactions/crossing
The LHC Environment
20 November 2007 Doris Eckstein, DESY Seminar 7
LHCb – a forward Spectrometer
•full spectrum of B-hadrons produced
bb
boost Lorentz
correlated bb
LHCb: equippes the forward direction15-250mrad acceptance
,.... 00bcsd Λ,B,B,B,B
~40% ~40% ~10% ~10%
•B-cross-section large ~500μb
•1012 b-hadrons per nominal year [107s] of data taking (2 fb-1)
b
b
b
b
bb
Does not occur
20 November 2007 Doris Eckstein, DESY Seminar 8
p p
250 mrad
10 mrad
Tracking systemVELOTrigger TrackerInner/Outer Tracker
Particle IDRICH1 and RICH2CalorimetersMuon system
KinematicsMagnet + TrackersCalorimeters
Vertex ReconstructionVELO
The Detector
20 November 2007 Doris Eckstein, DESY Seminar 9
LHCb – at Point 8
Muon Calorimeters RICH2Trackers
Magnet
RICH1VELO
20 November 2007 Doris Eckstein, DESY Seminar 10
Trigger
•Only ~1% of inelastic collisions produce b-quarks•Branching fractions of interesting B decays are <10-4
L0High pt hadron, lepton,
Flag multiple interactions, busy eventsHardware (custom boards), latency 4s
Calo, Muon, Pileup, SPD
HLTInclusive and exclusive selections
Software (PC farm 1800 nodes), complete event Full information from detector
On tape
10 MHz visible
1 MHz full detector readout
2 kHz 35 kB per event
Output rate
Trigger Type Physics Use
200 Hz Exclusive B candidates
Specific final states
600 Hz High Mass di-muons
J/, bJ/X
300 Hz D* Candidates Charm, calibrations
900 Hz Inclusive b (e.g. b)
B data mining
VELO Information for fast reconstruction Fast data reduction
20 November 2007 Doris Eckstein, DESY Seminar 11
VELO requirements
Measure proper time of B decay:
t = mB L / pc
decay length L (~ 1 cm in LHCb) momentum p from decay products
(which have ~ 1–100 GeV)
Tracker:
tracking before magnetcover full downstream detector acceptance 21 stations allowing to measure >=3hits/track
Num
ber
of h
its p
er p
artic
le
Pseudorapidity
20 November 2007 Doris Eckstein, DESY Seminar 12RF fo
il
interaction point
Silicon sensors
VELO requirements
1m
Interaction Region, 5,3 cm
Vertex detector:
•Reconstruct pp interaction vertex < 10μm wide spread of interaction region in z many stations around z=0
•Reconstruct B decay vertexshort track extrapolation distance andminimal multiple scattering IP < 40 μm
minimal material before first measured pointVELO sensors as close as possible to beam 7mm distance no beam pipe
20 November 2007 Doris Eckstein, DESY Seminar 13
Vacuum Vessel
secondary Vacuum box
retractable detector halves
vacuum feedthroughs
•Injection: larger aperture required allow for retraction by 30mm
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
In the Vacuum
20 November 2007 Doris Eckstein, DESY Seminar 14
Middle station
Far station
an example Vdep
R/cm
Vdep
•extremely inhomogeneous irradiation dependence on R and station (z)
•5x1012 to 1.3x1014 neq/cm2/year(compatible with other LHC detectors)
•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
Radiation environment
20 November 2007 Doris Eckstein, DESY Seminar 15
n+-on-n strips
Routing lines on 2nd metal layer
n+ implantsSiO2
p+ implant
Depletion fraction
reso
luti
on
p-on-n efficiency degrades fastn-on-n efficiency ~100% for only 60% depletion depth
n-on-n silicon, under-depleted:
•Limited loss in CCE
•Less resolution degradation
20 November 2007 Doris Eckstein, DESY Seminar 16
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
Φ-measuring sensor
•40-102μm (R Sensor)•36-97μm (Φ Sensor)•sensitive area from 8 to 42mm radius•300μm thickness
•Single sided •2048 channels per sensor•2 x 2 x 21 sensors 172 k channels
©PPARC
R measuring sensor2nd metal layer Pitch adaptor
RO chips
20 November 2007 Doris Eckstein, DESY Seminar 17
Module
•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
Hybrid
Cooling cookies
20 November 2007 Doris Eckstein, DESY Seminar 18
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 19
Insert modules
Assembly
Take an empty half Connect cooling and cables
•Electrical test to reveal problems•Log fingerprint of each module
S/N
Testpulse-S/N for all R-sensors
20 November 2007 Doris Eckstein, DESY Seminar 20
The signal chain
2048 x 84 channels produce dataneed online zero suppression
60m cat6 TELL1 board
To PC farm1MHz of data
20 November 2007 Doris Eckstein, DESY Seminar 21
Online zero suppression
ADC
FIR correction
Pedestal correction/Bit limit
Reordering
LCMS
Clustering
10 bit
8 bit
7 bit
•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 sophisticatedoffline reconstruction purposes Online cluster position calculated included in Cluster format as well as all cluster strip infoTELL1 Emulation for bit-perfect offline code development cut tuning, etc.
20 November 2007 Doris Eckstein, DESY Seminar 22
Online zero suppression
TELL1 Algorithm Cluster Seeding Threshold
Clu
ster
Fin
ding
Eff
icie
ncy
•Emulation developed and tested with testbeam and lab data•Keep control about what happens online
20 November 2007 Doris Eckstein, DESY Seminar 23
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 24
Beam
zy
x
VELO System Test – Testbeam Nov’06
20 November 2007 Doris Eckstein, DESY Seminar 25
Noise and S/N
Signal / Noise
Common Mode Subtracted Noise of Each Run
Run Time11/10/06 11/12/06 11/14/06 11/16/06 11/18/06 11/20/06
Ave
rage
Noi
se
0
1
2
3
4
R DetectorsPhi Detectors
HP1 HP2 HP3 HP4
• 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 26
Reconstructing the Vertex
d = 2mm
d = 5mm
15 mm
•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
Targets installed during testbeam
20 November 2007 Doris Eckstein, DESY Seminar 27
Reconstructing the Vertex
Target
• Vertex reconstructed from interaction between proton beam (180 GeV) and sensors or targets.
before alignment
…and after alignment
20 November 2007 Doris Eckstein, DESY Seminar 28
Sensor Resolution
40=8.4m 40=8.6m
• 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 29
Simulated Event
20 November 2007 Doris Eckstein, DESY Seminar 30
IP = 14m+35m/pT
Impact parameter resolution • proper time t=lm/p• Proper time resolution is dominated by
B vertex resolution
•Impact parameter resolution crucial for proper time resolution• ~40 fs for most channels
Bs→Ds
Detector Performance – Vertexing
20 November 2007 Doris Eckstein, DESY Seminar 31
From Assembly to Installation
20 November 2007 Doris Eckstein, DESY Seminar 32
Where it has to fit
What the beam sees Should be a perfect match
20 November 2007 Doris Eckstein, DESY Seminar 33
VELO Installation
It was electrically testedand it does work!No damage occured during theinstallation!Now Commissioning.
20 November 2007 Doris Eckstein, DESY Seminar 34
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 formerVELO colleagues!Good luck for the data taking enjoy the exciting time ahead!
20 November 2007 Doris Eckstein, DESY Seminar 35
• BACKUP
20 November 2007 Doris Eckstein, DESY Seminar 36
Tracking
T1, T2, T3 made ofOuter Tracker and Inner Tracker
Trigger Tracker•Measurement in fringe field of magnet•Covers full detector acceptanceProvide pt for Trigger (together with VELO)2*2 layersSilicon microstrip sensors500m thickness~200m readout pitch
Outer Tracker
Inner Tracker forRegion of high occupancy
cm
cm
20 November 2007 Doris Eckstein, DESY Seminar 37
Tracking
Inner Tracker:•only 2% of area, but 20% of tracks
Silicon microstrip sensors
•11 cm strips, ~200m 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 m thickness
Single sensors:320 m thickness
Tracking behind the Magnet – IT and OT
20 November 2007 Doris Eckstein, DESY Seminar 38
from Bs
→DsKus
sssB D*cbV
usV
b
Kc
cs
sssB K*cbV
csV
b
Du
• Expect 6200 DsK events in 2 fb–1
• B/S < 0.5
• Expect 6200 DsK events in 2 fb–1
• B/S < 0.5
• Expect 140 000 Ds• 98% suppression
achieved with RICH PID system in the analysis
• Used to measure ms
• 2 fb–1: (ms) 0.012ps–1
• Expect 140 000 Ds• 98% suppression
achieved with RICH PID system in the analysis
• Used to measure ms
• 2 fb–1: (ms) 0.012ps–1
+ ch.c. diagrams
• Study sensitivity by generating toy-experiments with experimental inputs derived from full MC (Decay time and mass resolution, reconstruction efficiency, tagging…)
– Sensitivity with 2 fb-1 : σ() ~ 13°
• Two tree decays (bc and bu), which interfere via Bs mixing:
– can determine (s + ), hence in a very clean way
• Fit 4 tagged, time-dependent rates
– Extract s + , strong phase difference , amplitude ratio
– Bs Ds also used in the fit to constrain other parameters (, ms, s)
Slide from Malcolm John
20 November 2007 Doris Eckstein, DESY Seminar 39
s
s
0sB
*tbV
tsV
b
b
0sB
t
t
*tsV
tbV
c
c
ss
0sB
/JcsV
cbVb
s
Bs mixing phase: s
• The equivalent of “sin2“ for Bs mesons• In the standard model, s is small: = -2arg(Vts) 0.0360.003
– Could be larger if New Physics is present in the box diagram– Recent D0 result s= –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 s : Bs→ J/Bs→ cBs→ J/ Bs→ Ds Ds
• Control channel (ms): Bs→ Ds
Illustration of CPV:
toy-modeling LHCb data with s = 0.2 (i.e. 5SM)
events tagged as Bs
events tagged as Bs
Slide from Malcolm John
20 November 2007 Doris Eckstein, DESY Seminar 40
Bs expected sensitivity
• 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 , b.
– Background analysis is currently limited by Monte Carlo statistics (generation)
• LHCb’s superior Bs invariant mass resolution is crucial in the background rejection
LHCb limit on BR at 90% CL (only bkg is observed)
LHCb sensitivity(signal+bkg is observed)
5 observation
3 evidence
SMB
F (
x10–9
)
Integrated luminosity (fb–1)
BF
(x1
0–9)
Expected final CDF+D0 limit
SM
“early”
period
Uncertainty in bkg prediction
Uncertainty in bkg prediction
Slide from Malcolm John
20 November 2007 Doris Eckstein, DESY Seminar 41
Noise
inner strip+ routingline
outer strip
No
ise
(AD
C c
nts
)
Φ R
inner outer
IncreasingStrip length
•Different noise levels understood,
primary reason strip geometry and routing
Total NoiseCM sub. Noise
20 November 2007 Doris Eckstein, DESY Seminar 42
red = detected hits
blue = reconstructed tracks
VELOTT
T1 T2 T3
Detector Performance – Tracking
•Momentum resolution p/p ~ 0.4%
•tracks passing through full spectrometer:
~ 95%, a few percent of ghost tracks
Mass resolution BsDs
Typical m~15 MeV