View
212
Download
0
Category
Tags:
Preview:
Citation preview
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 3
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 4
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)
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 5
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 6
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 7
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 8
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 9
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 10
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 11
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 12
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 13
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 14
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 15
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 16
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 17
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 18
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 19
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 20
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 21
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 22
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 23
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 24
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 25
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 26
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 27
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 28
Backup SlidesBackup Slides
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 29
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 30
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 31
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
G. Eigen, LISHEP2011, Rio de Janeiro, July 5th, 2011 32
J/ψ Candidate SelectionJ/ψ Candidate Selection
G. Eigen, Rio
Recommended