G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Outline Introduction Introduction ATLAS detector and performance Vertex and impact parameter resolution Exclusive B reconstruction B d 0 and B s 0 lifetimes Tagging performance Expectations by end of 2012 Conclusion

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Introduction Precision measurements in the B d 0 system by BABAR & Belle show that the phase in the CKM matrix is the main source of CP violation in B system Angle β is measured to 4%, angle α to 5% and angle γ to 35% New physics contributions are constrained to < O (10%) Next step is to measure CP violation in the B s 0 system studying time dependent decay rates for B s 0 and B s 0 dependent decay rates for B s 0 and B s 0 HFAG/CKMfitter 2010 SM: Lenz et al, hep-hp/

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Requirements for CPV Measurements The bb cross section in pp collisions at 7 TeV is huge  at high luminosities LHC produces gigantic B meson samples ATLAS has excellent capabilities to perform time-dependent to perform time-dependent decay rate measurements decay rate measurements Reconstruct exclusive final states with good resolution states with good resolution Measure vertices with high precision precision Tag b flavor at production with Q jet (validate with data) with Q jet (validate with data) B s 0  J/ψ  is most promising mode observed in ATLAS for β s observed in ATLAS for β s Need validation measurements in B d 0  J/ψK s 0 (for CPV), B d 0  J/ψK *0 (angular analysis) & B +  J/ψK + (tags) B d 0  J/ψK s 0 (for CPV), B d 0  J/ψK *0 (angular analysis) & B +  J/ψK + (tags)

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, The ATLAS Detector The fraction of operational channels is close to 100% for all systems

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Subdetectors Important for B Physics Inner Detector Inner Detector Solenoidal 2T B field Solenoidal 2T B field Coverage |η|<2.5 Coverage |η|<2.5 σ/p T ≅ 3.4×10 -4 p T for |η|<1.5 σ/p T ≅ 3.4×10 -4 p T for |η|<1.5 Muon system Muon system Precise tracking chambers & trigger chambers trigger chambers Coverage |η|<2.7 Coverage |η|< T torroidal field (average) 0.5 T torroidal field (average) σ/p T <0.1 up to 1 TeV σ/p T <0.1 up to 1 TeV TransistionRadiationTracker: e- π separation Tracking Silicon strips Tracking+vertex Silicon pixels vertex

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Luminosity ATLAS already has recorded an integrated luminosity 1.23 fb -1 integrated luminosity 1.23 fb -1 by end of June by end of June Delivered luminosity: 1.29 fb -1 Peak luminosity: 1.26 ✕ cm -2 s -1 Peak luminosity: 1.26 ✕ cm -2 s -1 Preliminary uncertainty on Preliminary uncertainty on 2011 luminosity: 4.5% 2011 luminosity: 4.5% Expect integrated luminosity >10 fb -1 by end of 2012 >10 fb -1 by end of 2012 L tot in 2011

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Data Recording Total efficiency is >95% Efficiency in the subsystems is % Efficiency in the subsystems is % Average number of interactions per crossing is 6

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Performance on Particle Reconstruction ATLAS reconstructs various particles with good resolution ATLAS reconstructs various particles with good resolution ATLAS also reconstructs D s +, Λ, Σ, Ω, Λ b, B d 0, B +, B s 0,… ATLAS also reconstructs D s +, Λ, Σ, Ω, Λ b, B d 0, B +, B s 0,… K 0 s mass D *+ -D 0 mass difference D + mass Φ mass Δ M=145.54±0.05 MeV σ ( Δ M)=0.85±0.05 MeV m D + =1871.8±86 MeV σ ( m D + )=19.7±1.2 MeV m Φ =1020.3±0.3 MeV σ ( m Φ )=2.3±0.5 MeV m π0 =134.0±0.8 MeV σ ( m π0 )=24MeV m K0s =±0.006 MeV σ ( m K0s )=2.3±0.5 MeV π 0 mass Barrel+EC

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Measurement of Primary Vertex Select fully reconstructed tracks with small transverse & longitudinal Select fully reconstructed tracks with small transverse & longitudinal impact parameter for primary vertex reconstruction impact parameter for primary vertex reconstruction Determine primary vertex with adaptive vertex fitting algorithm Determine primary vertex with adaptive vertex fitting algorithm Remove tracks that are more than 7σ incompatible with PV and use as Remove tracks that are more than 7σ incompatible with PV and use as seed for new vertex seed for new vertexResolution σ x =15.7 μm σ x =15.7 μm σ y =13.5 μm σ y =13.5 μm ATL-COM-PHYS

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Inner Detector Performance For precise measurements of secondary vertices, the secondary 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 pixels silicon pixels In the barrel measure σ=25 μm for hits from tracks with p T > 2 GeV hits from tracks with p T > 2 GeV In the EC measure σ=20 μm for In the EC measure σ=20 μm for hits from tracks with p T > 2 GeV hits from tracks with p T > 2 GeV ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Measure same J/ψ mass in different Measure same J/ψ mass in different η bins consistent with PDG value η bins consistent with PDG value Performance: J/ψ both μ ’s in barrel both μ ’s in EC ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Inclusive Dimuon Mass Spectrum The inclusive dimuon mass spectrum reveals known vector states We focus on exclusive final states with a J/ψ

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Muon Selection Define two sets of μ candidates used Define two sets of μ candidates used in the J/ψ selection in the J/ψ selection Combined μ (CB) : full muon spectrometer and track measurements in inner detector and track measurements in inner detector with a good fit between both regions Segment Tagged μ (ST) : track measurements in Inner Detector associated to at least one hit in muon spectrometer Muon efficiency L1 muon trigger efficiency ATLAS-CONF p T > 6 GeV

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, J/ψ Reconstruction Fit pairs of oppositely charged Fit pairs of oppositely charged muons to common vertex muons to common vertex Require at least 1 pixel hit Require at least 1 pixel hit & at least 4 SCT hits & at least 4 SCT hits Determine p T exclusively from Determine p T exclusively from Inner Detector track segment Inner Detector track segment Select J/ψ candidate in Select J/ψ candidate in mass windows mass windows MeV if both muons are in the barrel muons are in the barrel MeV for 1 muon MeV for 1 muon in barrel, other muon in endcap in barrel, other muon in endcap MeV if both muons are in the endcaps muons are in the endcaps J/ψ efficiency is uniform in p T at ~100% J/ ψ trigger efficiency systematic error 14

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, J/ψ Impact Parameter Resolution Look for bias in transverse impact parameter distribution Look for bias in transverse impact parameter distribution Mean value Mean value peaks at zero peaks at zero as expected as expected Mean value is uniform in η uniform in η and  and  Maximal Maximal deviation in deviation in η and  is η and  is less than less than 10 μm 10 μm ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Observation of B ±  J/ψ(μ + μ - )K ± Select additional track, assign kaon mass hypothesis Select additional track, assign kaon mass hypothesis Fit 3 track vertex; constrain μ + μ - mass to m(J/ψ) Do unbinned maximum likelihood fit with Gaussian signal & linear bg Enhance signal-to-background with transverse decay length cut Mass consistent with PDG Consistent results for B + & B - Mass consistent with PDG Consistent results for B + & B - m(J/ψ)= ±0.29 MeV m(J/ψ)= ±0.29 MeV after L xy >300 μ m ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Observation of B d 0  J/ψK *0 & B s 0  J/ψ  Select 2 additional tracks, assume K *0   K + π -,   K + K - Fit 4-track vertex; constrain μ + μ - mass to m(J/ψ) Apply mass cuts on K + π - around K *0 and on K + K - around  Do unbinned maximum likelihood fit with Gaussian signal & linear bg ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Observation of B d 0  J/ψK *0 & B s 0  J/ψ  Add decay time cut on fitted secondary vertex m B [MeV]σ m [MeV]N signal N background Bd0Bd0 no  cut5278.6± ± ± ±110 w  cut5279.6± ± ±801330±60 Bs0Bs0 no  cut5363.6± ±1.9413±36764±17 w  cut5364.0± ±1.6358±2290±7 Consistent Consistent with PDG with PDG masses massesGood mass mass resolution resolution ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Lifetime Measurement Methodology Select J/ψ candidate and add K + π - or K + K - to select J/ψK *0 or J/ψ  For each candidate calculate the proper decay time Precision is higher in the transverse plane Perform simultaneous unbinned maximum likelihood fit to reconstructed B d 0 (B s 0 ) masses and proper decay times Background contributions J/ψ from other B combined with random K + π - (K + K - ) J/ψX from signal B with/without random K + π - (K + K - ) Direct J/ψ production with random K + π - (K + K - ) L: distance between primary vertex & B decay vertex βγ : Lorentz boost factor ≅ p/m c: speed of light L xy : L in the transverse plane p T : transverse momentum m: B invariant mass

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, PDFs in ML Fit Signal mass is parameterized by a Gaussian using scale factor in width Signal mass is parameterized by a Gaussian using scale factor in width Background mass distribution is modeled with a linear function Signal proper decay time pdf is exponential decay convolved with Gaussian resolution function R( τ ’- τ,δ τi ) with width Gaussian resolution function R( τ ’- τ,δ τi ) with width Background with J/ψ from other B is parameterized by Background of direct J/ψ is parameterized by d: slope m C =(m max -m min )/2 S m : scale factor S τ scale factor τ eff1, τ eff2, τ eff3 are 3 background lifetimes Determined in fit

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Results for B d 0  J/ψK *0 Keep 12 parameters free in ML fit: f sig, m B, S m, d, τ B, S τ, 3 background lifetimes and 3 background fractions lifetimes and 3 background fractions Measure: Measure: Good agreement with PDG value Good agreement with PDG value ATLAS-CONF ±90 signal events

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Results for B s 0  J/ψ  Measure Measure Good agreement with HFAG value In B s 0  J/ψ  CP-even and CP odd components that have different lifetimes are not symmetric  τ differs from generic B s lifetime lifetimes are not symmetric  τ differs from generic B s lifetime ATLAS-CONF ±26 signal events

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, B Flavor Tagging For tagging of B flavor at production use lepton charge or jet charge The jet charge is positive for b jets and negative for b jets Jet consists of all tracks with p T > 500 MeV, |η| 500 MeV, |η|<2.5 inside a cone with opening angle opening angle Remove cases where jet charge is close to zero by “exclusion cut” Remove cases where jet charge is close to zero by “exclusion cut” Key quantities in tagging are efficiency and dilution The true asymmetry & its error are given by

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, b Flavor Tagging in Simulation Tagging effectiveness is given by Tagging effectiveness is given by Study jet charge in B d 0  J/ψK *0 or B s 0  J/ψ  Study jet charge in B d 0  J/ψK *0 or B s 0  J/ψ  For simulation assume signal events expected for 150 pb -1 in B d 0  J/ψK *0 & 1.5fb -1 expected for 150 pb -1 in B d 0  J/ψK *0 & 1.5fb -1 in B s 0  J/ψ  in B s 0  J/ψ  Simultaneous mass & lifetime fit Simultaneous mass & lifetime fit Optimize selection Achieve high efficiency & reasonable dilution reasonable dilution For lepton tags expect higher purity but lower efficiency, ISBN

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Estimated J/ψ  Signal Yields by End 2012 Use ATLAS and LHCb observed J/ψ  signal yields to estimate J/ψ  signal yields to estimate expectation at end of 2012 expectation at end of 2012 ATLAS observes 358±22 signal events in 40 pb -1 after a 0.4ps lifetime cut in 40 pb -1 after a 0.4ps lifetime cut For 10 fb -1 with the same trigger conditions, ATLAS expects conditions, ATLAS expects 89500±5500 J/ψ  signal events 89500±5500 J/ψ  signal events Increased trigger thresholds may reduce this yield by 50% yield by 50% LHCb sees 760±29 J/ψ  signal events in 36pb -1 LHCb sees 760±29 J/ψ  signal events in 36pb -1 For 2 fb -1 (corresponds to 10 fb -1 in ATLAS) For 2 fb -1 (corresponds to 10 fb -1 in ATLAS) LHCb expects 42222±1611 J/ψ  signal events LHCb expects 42222±1611 J/ψ  signal events ATLAS will make a valuable contribution ATLAS will make a valuable contribution to the determination of β s to the determination of β s m=5363±.8 MeV σ =18.4±.7 MeV LHCb-CONF ATLAS-CONF

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Conclusions ATLAS is a well-working detector recording data with high efficiency ATLAS has an excellent capability to measure secondary vertices, tag the b flavor at production with high tagging effectiveness and tag the b flavor at production with high tagging effectiveness and reconstruct B exclusive final states with excellent mass resolution and reconstruct B exclusive final states with excellent mass resolution and high efficiency high efficiency ATLAS measures B +  J/ψK +, B d 0  J/ψK *0 & B d 0  J/ψ  signals ATLAS measures B +  J/ψK +, B d 0  J/ψK *0 & B d 0  J/ψ  signals with low background with low background ATLAS performes first lifetime measurements in B d 0  J/ψK *0 & ATLAS performes first lifetime measurements in B d 0  J/ψK *0 & B d 0  J/ψ  B d 0  J/ψ  Thus, ATLAS has excellent capabilities to measure CPV in B decays

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Backup Slides

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Trigger Operations Trigger is organized in 3 levels L1: hardware trigger  50 kHz rate L2: software selection on L2: software selection on reduced granularity (ROI) reduced granularity (ROI)  4 kHz rate EF: Based on offline reconstruction, full granularity reconstruction, full granularity  200 Hz rate design with peak to 600 Hz peak to 600 Hz Rates of physics objects are very Rates of physics objects are very well understood well understood Physics rate is ~300 Hz Physics rate is ~300 Hz

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, Systematic Errors in B d 0 & B s 0 Lifetimes Modeling of signal and background in ML fit  use alternative parameterization  use alternative parameterization Fit procedure  run several thousand  run several thousand toy experiments toy experiments Mass window  for B d 0 vary window (5169, 5389) MeV to (5079, 5479) MeV in 14 steps (5169, 5389) MeV to (5079, 5479) MeV in 14 steps  for B s 0 vary (5150, 5650) MeV to (5220, 5510) MeV in 11 steps  for B s 0 vary (5150, 5650) MeV to (5220, 5510) MeV in 11 steps Time uncertainty model  assume different proper time decay models Choice of primary vertex Choice of primary vertex  use different impact parameter calculation

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, ATLAS Subsystem Operation Fraction of operational channels is close to 100% for all systems

G. Eigen, LISHEP2011, Rio de Janeiro, July 5 th, J/ψ Candidate Selection G. Eigen, Rio