g. eigen, lishep2011, rio de janeiro, july 5 th, 20112 outline introduction introduction atlas...

G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 2

OutlineOutline

IntroductionIntroduction

ATLAS detector and performanceATLAS detector and performance

Vertex and impact parameter resolutionVertex and impact parameter resolution

Exclusive B reconstructionExclusive B reconstruction

BBdd00 and B and Bss

00 lifetimes lifetimes

Tagging performanceTagging performance

Expectations by end of 2012Expectations by end of 2012

ConclusionConclusion


IntroductionIntroduction

Precision measurements in the BPrecision measurements in the Bdd00 system by BABAR & Belle show system by BABAR & Belle show

that the phase in the CKM matrix is the main source of CP violation that the phase in the CKM matrix is the main source of CP violation in B systemin B system

Angle β is measured to 4%, angle α to 5% and angle γ to 35%Angle β is measured to 4%, angle α to 5% and angle γ to 35%

New physics contributions are constrained to < New physics contributions are constrained to < OO(10%)(10%)

Next step is to measure CP violation in the BNext step is to measure CP violation in the Bss00 system studying system studying

time time dependent decay rates for Bdependent decay rates for Bss

00 and B and Bss00

HFAG/CKMfitter 2010SM: Lenz et al, hep-hp/1008.1593


Requirements for CPV MeasurementsRequirements for CPV Measurements

The bb cross section in pp collisions at 7 TeV is huge The bb cross section in pp collisions at 7 TeV is huge at high at high luminosities LHC produces gigantic B meson samplesluminosities LHC produces gigantic B meson samples

ATLAS has excellent capabilitiesATLAS has excellent capabilities to perform time-dependentto perform time-dependent decay rate measurementsdecay rate measurements

Reconstruct exclusive finalReconstruct exclusive final states with good resolutionstates with good resolution

Measure vertices with high Measure vertices with high precisionprecision

Tag b flavor at production Tag b flavor at production with with QQjetjet (validate with data) (validate with data)

BBss00J/ψJ/ψΦΦis most promising modeis most promising mode

observed in ATLAS for observed in ATLAS for ββss

Need validation measurements inNeed validation measurements in BBdd

00J/ψKJ/ψKss00 (for CPV), (for CPV), BBdd

00J/ψKJ/ψK*0 *0 (angular analysis) & (angular analysis) & BB++J/ψKJ/ψK+ +

(tags)(tags)


The ATLAS DetectorThe ATLAS Detector

The fraction of operational channels is close to 100% for all The fraction of operational channels is close to 100% for all systemssystems


Subdetectors Important for B Subdetectors Important for B PhysicsPhysics

Inner DetectorInner Detector

Solenoidal 2T B fieldSolenoidal 2T B field

Coverage |η|<2.5Coverage |η|<2.5

σ/pσ/pT T ≅≅ 3.4×10 3.4×10-4-4 p pTT +0.015 for |η| +0.015 for |η|

<1.5<1.5

Muon systemMuon system

Precise tracking chambers &Precise tracking chambers & trigger chamberstrigger chambers

Coverage |η|<2.7Coverage |η|<2.7

0.5 T torroidal field (average)0.5 T torroidal field (average)

σ/pσ/pT T <0.1 up to 1 TeV<0.1 up to 1 TeV

TransistionTransistionRadiation Radiation Tracker:Tracker:e-e-ππ separation separationTrackingTracking

Silicon stripsSilicon stripsTracking+Tracking+vertexvertex

Silicon pixelsSilicon pixelsvertexvertex


LuminosityLuminosity

ATLAS already has recorded anATLAS already has recorded an integrated luminosity integrated luminosity 1.23 fb1.23 fb-1-1

by end of Juneby end of June

Delivered luminosity: 1.29 fbDelivered luminosity: 1.29 fb-1-1

Peak luminosity: 1.26Peak luminosity: 1.26✕✕10103333 cm cm-2-2ss-1-1

Preliminary uncertainty on Preliminary uncertainty on 2011 luminosity: 4.5%2011 luminosity: 4.5%

Expect integrated luminosity Expect integrated luminosity >10 fb>10 fb-1-1 by end of 2012by end of 2012

LLtottot in 2011 in 2011


Data RecordingData Recording Total efficiency is Total efficiency is >95%>95%

Efficiency in the subsystems is 90-100%Efficiency in the subsystems is 90-100%

Average number of interactions per crossing is 6Average number of interactions per crossing is 6


Performance on Particle Performance on Particle ReconstructionReconstruction

ATLAS reconstructs various particles with good resolution ATLAS reconstructs various particles with good resolution

ATLAS also reconstructs DATLAS also reconstructs Dss++, Λ, Σ, Ω, Λ, Λ, Σ, Ω, Λbb, B, Bdd

00, B, B++, B, Bss00,…,…

K0s mass

D*+-D0 mass difference D+ mass Φ mass

ΔM=145.54±0.05 MeVσ(ΔM)=0.85±0.05 MeV

mD+ =1871.8±86 MeVσ(mD+)=19.7±1.2 MeV

mΦ =1020.3±0.3 MeVσ(mΦ)=2.3±0.5 MeV

mπ0 =134.0±0.8 MeVσ(mπ0)=24MeV

mK0s 497.427=±0.006 MeVσ(mK0s)=2.3±0.5 MeV

π0 mass

Barrel+EC


Measurement of Primary VertexMeasurement of Primary Vertex

Select fully reconstructed tracks with small transverse & Select fully reconstructed tracks with small transverse & longitudinallongitudinal

impact parameter for primary vertex reconstructionimpact parameter for primary vertex reconstruction

Determine primary vertex with adaptive vertex fitting algorithmDetermine primary vertex with adaptive vertex fitting algorithm

Remove tracks that are more than 7σ incompatible with PV and Remove tracks that are more than 7σ incompatible with PV and

use asuse as seed for new vertexseed for new vertex

Resolution Resolution

σσxx=15.7 μm=15.7 μm

σσyy=13.5 μm=13.5 μm

ATL-COM-PHYS-2011-571


Inner Detector PerformanceInner Detector Performance

For precise measurements of For precise measurements of secondary vertices, thesecondary vertices, the performance of the Inner Detector performance of the Inner Detector is crucial, particularly that of the is crucial, particularly that of the silicon pixelssilicon pixels

In the barrel measure In the barrel measure σ=25 μm σ=25 μm forfor hits from tracks with phits from tracks with pTT> 2 GeV > 2 GeV

In the EC measure In the EC measure σ=20 μm σ=20 μm forfor hits from tracks with phits from tracks with pTT> 2 GeV > 2 GeV

ATLAS-CONF-2011-012


Measure same J/ψ mass in differentMeasure same J/ψ mass in different η bins consistent with PDG valueη bins consistent with PDG value

Performance: J/ψPerformance: J/ψ

both both μμ’s’sin barrelin barrel

both both μμ’s’sin ECin EC

ATLAS-CONF-2010-078 11


Inclusive Dimuon Mass SpectrumInclusive Dimuon Mass Spectrum The inclusive dimuon mass spectrum reveals known vector The inclusive dimuon mass spectrum reveals known vector

statesstates

We focus on exclusive final states with a We focus on exclusive final states with a J/ψJ/ψ


Muon SelectionMuon Selection

Define two sets of μ candidates used Define two sets of μ candidates used in the J/ψ selectionin the J/ψ selection

Combined Combined μ (μ (CBCB)): full muon spectrometer : full muon spectrometer and track measurements in inner detectorand track measurements in inner detectorwith a good fit between both regionswith a good fit between both regions

Segment Tagged Segment Tagged μ (μ (STST)): track measurements: track measurementsin Inner Detector associated to at least onein Inner Detector associated to at least onehit in muon spectrometerhit in muon spectrometer

Muon efficiency

L1 muon trigger efficiencyL1 muon trigger efficiency

ATLAS-CONF-2011-021

pT> 6 GeV


J/ψ ReconstructionJ/ψ Reconstruction

Fit pairs of oppositely chargedFit pairs of oppositely charged muons to common vertexmuons to common vertex

Require at least 1 pixel hitRequire at least 1 pixel hit & at least 4 SCT hits& at least 4 SCT hits

Determine pDetermine pTT exclusively from exclusively from Inner Detector track segmentInner Detector track segment

Select J/ψ candidate in Select J/ψ candidate in mass windowsmass windows

2959-3229 MeV 2959-3229 MeV if bothif both muons are in the barrelmuons are in the barrel

2913-3273 MeV 2913-3273 MeV for 1 muonfor 1 muon in barrel, other muon in endcapin barrel, other muon in endcap

2852-3332 MeV 2852-3332 MeV if bothif both muons are in the endcapsmuons are in the endcaps

J/ψ efficiency is uniform in pJ/ψ efficiency is uniform in pT T at ~100% at ~100%

J/ψ trigger efficiency

systematic error

14


J/ψ Impact Parameter ResolutionJ/ψ Impact Parameter Resolution Look for bias in transverse impact parameter distributionLook for bias in transverse impact parameter distribution

Mean valueMean value peaks at zeropeaks at zero as expectedas expected

Mean value isMean value is uniform in ηuniform in η and and ΦΦ

Maximal Maximal deviation indeviation in η and η and ΦΦ is is less than less than 10 μm10 μm ATLAS-CONF-2011-012


Observation of BObservation of B±±J/ψ(μJ/ψ(μ++μμ--)K)K±±

Select additional track, assign kaon mass hypothesisSelect additional track, assign kaon mass hypothesis

Fit 3 track vertex; constrain μFit 3 track vertex; constrain μ++μμ- - mass to m(J/ψ)mass to m(J/ψ)

Do unbinned maximum likelihood fit with Gaussian signal & linear Do unbinned maximum likelihood fit with Gaussian signal & linear

bgbg

Enhance signal-to-background with transverse decay length cutEnhance signal-to-background with transverse decay length cut

Mass consistent with PDG Consistent results for BMass consistent with PDG Consistent results for B++ & B & B-- m(J/ψ)=5279.17±0.29 MeVm(J/ψ)=5279.17±0.29 MeV

afterLxy >300μm

ATLAS-CONF-2010-098


Observation of BObservation of Bdd00J/ψKJ/ψK*0 *0 & & BBss

00J/ψJ/ψΦΦ

Select 2 additional tracks, assume KSelect 2 additional tracks, assume K*0*0KK++ππ--, , ΦΦ KK++KK--

Fit 4-track vertex;Fit 4-track vertex; constrain μconstrain μ++μμ- - mass to m(J/ψ)mass to m(J/ψ)

Apply mass cuts on KApply mass cuts on K++ππ- - around Karound K*0*0 and on K and on K++KK- - around around ΦΦ

Do unbinned maximum likelihood fit with Gaussian signal & Do unbinned maximum likelihood fit with Gaussian signal &

linear bglinear bg

ATLAS-CONF-2011-050


Observation of BObservation of Bdd00J/ψKJ/ψK*0 *0 & & BBss

00J/ψJ/ψΦΦ

Add decay time cut on fitted secondary vertex Add decay time cut on fitted secondary vertex

mB [MeV] σm [MeV]

Nsignal Nbackground

Bd0 no τ cut 5278.6±1.

336.8±2.0 2680±15

010280±110

w τ cut 5279.6±0.9

38.8±1.2 2340±80 1330±60

Bs0 no τ cut 5363.6±1.

621.9±1.9 413±36 764±17

w τ cut 5364.0±1.4

26.6±1.6 358±22 90±7

ConsistentConsistent

with PDGwith PDG massesmasses

GoodGood massmass resolution resolution ATLAS-CONF-2011-050


Lifetime Measurement MethodologyLifetime Measurement Methodology

Select J/ψ candidate and add KSelect J/ψ candidate and add K++ππ- - or Kor K++KK-- to select J/ψK to select J/ψK*0*0 or J/ψ or J/ψΦΦ For each candidate calculate the proper decay timeFor each candidate calculate the proper decay time

Precision is higher in the transverse plane Precision is higher in the transverse plane

Perform simultaneous unbinned maximum likelihood fit to reconstructed Perform simultaneous unbinned maximum likelihood fit to reconstructed BBdd

00 (B (Bss00) masses and proper decay times) masses and proper decay times

Background contributionsBackground contributions J/ψ from other B combined with random KJ/ψ from other B combined with random K++ππ-- (K (K++KK--)) J/ψX from signal B with/without random KJ/ψX from signal B with/without random K++ππ-- (K (K++KK--)) Direct J/ψ production with random KDirect J/ψ production with random K++ππ-- (K (K++KK--))

L: distance between primary vertex & B decay vertexβγ: Lorentz boost factor ≅ p/mc: speed of light

Lxy: L in the transverse planepT: transverse momentumm: B invariant mass


PDFs in ML FitPDFs in ML Fit Signal mass is parameterized by a Gaussian using scale factor in Signal mass is parameterized by a Gaussian using scale factor in

widthwidth

Background mass distribution is modeled with a linear functionBackground mass distribution is modeled with a linear function

Signal proper decay time pdf is exponential decay convolved withSignal proper decay time pdf is exponential decay convolved with Gaussian resolution function R(Gaussian resolution function R(ττ’-’-τ,δτ,δτiτi) with width ) with width

Background with J/ψ from other B is parameterized byBackground with J/ψ from other B is parameterized by

Background of direct J/ψ is parameterized by Background of direct J/ψ is parameterized by

d: slopemC=(mmax-mmin)/2

Sm: scale factor

Sτ scale factor

τeff1, τeff2, τeff3 are 3background lifetimes Determined in fit


Results for BResults for Bdd00J/ψKJ/ψK*0 *0

Keep 12 parameters free in ML fit: fKeep 12 parameters free in ML fit: fsigsig, m, mBB, S, Smm, d, τ, d, τBB, S, Sττ, 3 background, 3 background lifetimes and 3 background fractionslifetimes and 3 background fractions

Measure:Measure:

Good agreement with PDG value Good agreement with PDG value

ATLAS-CONF-2011-092

2950±90 signal events


Results for BResults for Bss00J/ψJ/ψΦΦ

MeasureMeasure

Good agreement with HFAG valueGood agreement with HFAG value

In In BBss00J/ψJ/ψΦΦ CP-even and CP odd components that have different CP-even and CP odd components that have different

lifetimes are not symmetric lifetimes are not symmetric τ differs from generic B τ differs from generic Bss lifetime lifetime ATLAS-CONF-2011-092

463±26 signal events


B Flavor TaggingB Flavor Tagging For tagging of B flavor at production use lepton charge or jet For tagging of B flavor at production use lepton charge or jet

chargecharge

The jet charge is positive for b jets and negative for b jetsThe jet charge is positive for b jets and negative for b jets

Jet consists of all tracks with pJet consists of all tracks with pT T > 500 MeV, |η|<2.5 inside a cone > 500 MeV, |η|<2.5 inside a cone withwith

opening angle opening angle Remove cases where jet charge is close to zero by “exclusion Remove cases where jet charge is close to zero by “exclusion

cut”cut”

Key quantities in tagging are efficiency and dilution Key quantities in tagging are efficiency and dilution

The true asymmetry & its error are given byThe true asymmetry & its error are given by


b Flavor Tagging in b Flavor Tagging in SimulationSimulation

Tagging effectiveness is given byTagging effectiveness is given by

Study jet charge in BStudy jet charge in Bdd00J/ψKJ/ψK*0*0 or B or Bss

00J/ψJ/ψΦΦ

For simulation assume 15000 signal events For simulation assume 15000 signal events expected for 150 pbexpected for 150 pb-1-1 in B in Bdd

00J/ψKJ/ψK*0*0 & 1.5fb & 1.5fb-1-1

in Bin Bss00J/ψJ/ψΦΦ

Simultaneous mass & lifetime fitSimultaneous mass & lifetime fit

Optimize selectionOptimize selection Achieve high efficiency &Achieve high efficiency & reasonable dilutionreasonable dilution

For lepton tags expect higher For lepton tags expect higher purity but lower efficiency, purity but lower efficiency,

ISBN978-92-9083-321-5


Estimated J/ψEstimated J/ψΦΦ Signal Yields by End Signal Yields by End 2012 2012

Use ATLAS and LHCb observedUse ATLAS and LHCb observed J/ψJ/ψΦΦ signal yields to estimate signal yields to estimate expectation at end of 2012expectation at end of 2012

ATLAS observes ATLAS observes 358±22 signal 358±22 signal eventsevents in 40 pbin 40 pb-1-1 after a 0.4ps lifetime cut after a 0.4ps lifetime cut

For For 10 fb10 fb-1-1 with the same triggerwith the same trigger conditions, ATLAS expectsconditions, ATLAS expects 89500±5500 89500±5500 J/ψJ/ψΦΦ signal events signal events

Increased trigger thresholds may reduce thisIncreased trigger thresholds may reduce this yield by 50%yield by 50%

LHCb sees LHCb sees 760±29 760±29 J/ψJ/ψΦΦ signal events in 36pb signal events in 36pb-1-1

For For 2 fb2 fb-1-1 (corresponds to 10 fb(corresponds to 10 fb-1-1 in ATLAS) in ATLAS) LHCb expects LHCb expects 42222±1611 42222±1611 J/ψJ/ψΦΦ signal events signal events

ATLAS will make a valuable contribution ATLAS will make a valuable contribution to the determination of βto the determination of βss

m=5363±.8 MeVσ=18.4±.7 MeV

LHCb-CONF-2011-014

ATLAS-CONF-2011-050


ConclusionsConclusions ATLAS is a well-working detector recording data with high ATLAS is a well-working detector recording data with high

efficiencyefficiency

ATLAS has an excellent capability to measure secondary vertices, ATLAS has an excellent capability to measure secondary vertices, tag the b flavor at production with high tagging effectiveness andtag the b flavor at production with high tagging effectiveness and reconstruct B exclusive final states with excellent mass resolution reconstruct B exclusive final states with excellent mass resolution

andand high efficiencyhigh efficiency

ATLAS measures BATLAS measures B++J/ψKJ/ψK++, , BBdd00J/ψKJ/ψK*0 *0 && BBdd

00J/ψJ/ψΦΦ signals signals with low backgroundwith low background

ATLAS performes first lifetime measurements in BATLAS performes first lifetime measurements in Bdd00J/ψKJ/ψK*0 *0 &&

BBdd00J/ψJ/ψΦΦ

Thus, ATLAS has excellent capabilities to measure CPV in B decaysThus, ATLAS has excellent capabilities to measure CPV in B decays


Backup SlidesBackup Slides


Trigger OperationsTrigger Operations

Trigger is organized in 3 levelsTrigger is organized in 3 levels L1: hardware trigger L1: hardware trigger

50 kHz rate50 kHz rate L2: software selection onL2: software selection on

reduced granularity (ROI)reduced granularity (ROI)

4 kHz rate4 kHz rate EF: Based on offline EF: Based on offline

reconstruction, full granularityreconstruction, full granularity

200 Hz rate design with200 Hz rate design with peak to 600 Hzpeak to 600 Hz

Rates of physics objects are veryRates of physics objects are very well understoodwell understood

Physics rate is ~300 HzPhysics rate is ~300 Hz


Systematic Errors in BSystematic Errors in Bdd0 0 & B& Bss

00 Lifetimes Lifetimes

Modeling of signal and background in ML fitModeling of signal and background in ML fit use alternative parameterizationuse alternative parameterization

Fit procedure Fit procedure

run several thousand run several thousand toy experimentstoy experiments

Mass window Mass window

for Bfor Bdd0 0 vary windowvary window

(5169, 5389) MeV to (5079, 5479) MeV in 14 steps(5169, 5389) MeV to (5079, 5479) MeV in 14 steps for Bfor Bss

00 vary vary (5150, 5650) MeV to (5220, 5510) MeV in 11 steps(5150, 5650) MeV to (5220, 5510) MeV in 11 steps

Time uncertainty modelTime uncertainty model

assume different proper time decay modelsassume different proper time decay models

Choice of primary vertexChoice of primary vertex

use different impact parameter calculationuse different impact parameter calculation


ATLAS Subsystem OperationATLAS Subsystem Operation

Fraction of operational channels is close to 100% for all systemsFraction of operational channels is close to 100% for all systems


J/ψ Candidate SelectionJ/ψ Candidate Selection

G. Eigen, Rio

g. eigen, lishep2011, rio de janeiro, july 5 th, 20112 outline introduction introduction atlas...

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