The LHCb VErtex LOcator Doris Eckstein Universität Hamburg, Institut für Experimentalphysik The LHCb Experiment - Motivation The LHCb Detector The VErtex

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

http://lhcb-vd.web.cern.ch/lhcb-vd/images/Velo.jpg

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


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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


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:


• 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


•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


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


p p

250 mrad

10 mrad

Tracking systemVELOTrigger TrackerInner/Outer Tracker

Particle IDRICH1 and RICH2CalorimetersMuon system

KinematicsMagnet + TrackersCalorimeters

Vertex ReconstructionVELO

The Detector


LHCb – at Point 8

Muon Calorimeters RICH2Trackers

Magnet

RICH1VELO


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


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


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


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


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


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


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


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


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


The signal chain

2048 x 84 channels produce dataneed online zero suppression

60m cat6 TELL1 board

To PC farm1MHz of data


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.


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


Cross talk

•Cross talk varied between 5 and 20%

•analysis developed and FIR corrections extracted

•Implemented in alignment with dramatic improvement in residual distributions


Beam

zy

x

VELO System Test – Testbeam Nov’06


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


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


Reconstructing the Vertex

Target

• Vertex reconstructed from interaction between proton beam (180 GeV) and sensors or targets.

before alignment

…and after alignment


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


Simulated Event


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


From Assembly to Installation


Where it has to fit

What the beam sees Should be a perfect match


VELO Installation

It was electrically testedand it does work!No damage occured during theinstallation!Now Commissioning.


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!


• BACKUP


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


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


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


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



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



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


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

Documents

The LHCb VErtex LOcator Doris Eckstein Universität Hamburg, Institut für Experimentalphysik The LHCb Experiment - Motivation The LHCb Detector The VErtex