1. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  1/19 High Precision Measurements of B s Parameters in B s  J/ψ  Roger Jones University of Lancaster United Kingdom for the ATLAS B-physics Group Beauty 2005, Assisi, Italy

2. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  2/19 Overview of ATLAS Weight: 7000 tonnes Radius: 11m Length: 46m Muon chambers Barrel toroid Inner detector EM calorimeter Forward calorimeter Hadronic calorimeter End-cap toroid

3. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  3/19 The LHC Environment pp collisions: 14 TeV centre of mass energy Luminosity: –2007: 50 days @ 0.5 x 10 33 cm -2 s -1 Tuning –2008-2009: 200 days @ 2 x 10 33 cm -2 s -1 “Low” –2010+: 10 34 cm -2 s -1 “High” –Drops by factor ~2 during 10 hour run 1 proton bunch crossing every 25ns –4.6/23 pp collisions/crossing @ low/high luminosity –~1% of pp collisions produce a bb pair At luminosity 2 x 10 33 cm -2 s -1 – bb events produced with rate of 10 6 Hz –10Hz output to permanent storage for B-physics so highly selective and adaptable B-physics trigger required

4. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  4/19 B-physics trigger strategies (see Natalia Panikashvili) As luminosity drops during the fill, more triggers are turned on TriggerLVL1LVL2 & event filterExample channels Di-muon L @ 2.10 33 (L ≈ 10 34 ) 2 muons p T > 6 GeV (barrel) 3 GeV (end-caps) Confirm muons Refit tracks in ID Decay vertex reconstr. Select decays using mass/decay length cuts B d → J/ψ(μμ)K 0 S B s → J/ψ(μμ)φ B → μμ B → K 0 *μμ B →  μμ Λ b → Λ 0 J/ψ(μμ) Λ b → Λ 0 μμ EM+μ L < 2.10 33 1 muon p T > 6 GeV 1 EM cluster E T > 2GeV Confirm muons & EMC Decay vertex reconstr. Refit tracks Selections B d → J/ψ(μμ)K 0 S + b→ eX B d → J/ψ(ee)K 0 S + b→ μX B d → K 0 *  B s →   + b→ μX Hadronic L < 2.10 33 1 muon p T > 6 GeV 1 jet cluster E T > 5GeV Confirm muons & j.c. Decay vertex reconstr. Refit tracks Selections B s →D s (φ(KK))π B s →D s (φ(KK)) a 1 (ρ 0 π + ) B + → K + K +  - B d →  +  - (+ b→ μX)

5. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  5/19 B s -B s mixing  S : mixing phase = 2 sin θ c sin γ |V ub | / |V cb | –Arises through the interference of mixing and decay –Highly sensitive to SUSY contributions –Parameter is small in the Standard Model (~0.02) so challenging measurement General box diagrams for B s -B s mixing: Γ s = ½ ( Γ H + Γ L ) ΔΓ s = Γ L – Γ H ΔM s = M H – M L X s = ΔM s / Γ s

6. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  6/19 B S →J/ψ   11 22 A ┴ A ║ A 0 Extracting mixing parameters requires separation of CP eigenstate amplitudes Scalar  Vector + Vector decay: final state described by three helicity amplitudes Determined by the angular distribution of the decay, and also proper times and tag p p B0SB0S K+K+ J/  --  ++ K-K- 1 2 3 Transversity basis: linear combinations of helicity amplitudes which are CP-eigenstates. Complete determination yields mixing parameters 4 J/ψ  B0SB0SB0SB0S B0SB0SB0SB0S μ+μ-μ+μ-μ+μ-μ+μ- K+K-K+K-K+K-K+K-

7. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  7/19 Decay parameterization 3 transversity amplitudes –2 independent magnitudes and 2 independent phases: |A ║ | |A ┴ | δ 1 δ 2 3 mixing parameters, 1 weak phase  Γ s ΔΓ s ΔM s  S  8 parameters to be extracted from the data

8. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  8/19 Theoretical distribution + h.c. Distribution is model-independent – new physics enters through the modification of existing values Accurately modelled by EvtGen

9. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  9/19 Is it a B or a B? (Tagging) b/b? Signal B/B-meson Jet charge tag b/b? Lepton tag from semi-leptonic decay For B d(s) → J/ψ(μ6μ3)K 0 S Tagging efficiency ε tag = 0.64 (0.62) Wrong-tag fraction W tag = 0.42 (0.39) ε tag(electron) = 0.012 ε tag(muon) = 0.025 W tag(electron) = 0.27 W tag(muon) = 0.24 Signal B/B-meson

10. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  10/19 The workflow 1 2 EVENT GENERATION: PythiaB, EvtGen SIMULATION/DIGITIZATION/RECONSTRUCTION 3 ‘AS REAL’ ANALYSIS 4 PARAMETER EXTRACTION: maximum likelihood using detector performance parameters derived from full simulation.

11. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  11/19 Details of Analysis All studies based on fully simulated ATLAS events and using the current reconstruction software –1 000 000 B s decays produced with PythiaB and EvtGen to generate the correct angular distribution and mixing (model input: A ┴,A ║, δ 1,δ 2,Γ s,ΔΓ s,  s,ΔM s ) –Cuts: 1 muon > 6 GeV; 1 muon > 3 GeV; kaons > 0.5 GeV  B S →J/ψ(μμ)  (KK) All computations performed and all results stored on the Grid (LCG)

12. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  12/19 ‘As real’ Analysis Fit track pairs to J/ψ hypothesis: –p T (μ 1 ) > 3GeV && p T (μ 2 ) > 3GeV –|η(μ)| < 2.4 –χ 2 /DoF < 6 && m(J/ψ) Є (-3σ,3σ) –σ = 38MeV Fit track pairs to  hypothesis –p T (K) > 0.5GeV –|η(K)| < 2.4  –χ 2 /DoF < 6 && m(  ) Є (1009.2, 1029.6) GeV J/ψ invariant mass  invariant mass

13. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  13/19 ‘As real’ Analysis B S fit –Four-track fit to single vertex; χ 2 /DoF < 10 –must point at primary vertex –B s proper decay time > 0.5ps –p T (B s ) > 10 GeV –m(B s ) Є (-3σ,3σ); σ = 17MeV B s invariant mass B s proper decay time

14. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  14/19 Analysis Results and projections Reconstruction Efficiency Number of events after 30 fb -1 Signal events with 4 reconstructed tracks 86.9%542 000 Signal J/ψ reconstructed80.6%502 700 Signal  reconstructed 72.6%452 800 Successful Bs fits53.4%333 000 After cuts43.4%270 700 Total number of signal events within kinematic cuts after 30 fb -1 : 810 000 LVL1/LVL2 trigger di-muon efficiency: 77% Number of signal events after trigger: 623 700

15. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  15/19 Background analysis Background 1: Identical spin structure and topology to signal –S/B ~ 15.1 B d →J/ψ(μμ)K 0 *(K + π - ) (background 1) bb→J/ψ(μμ)X (background 2) Background 2: Angular structure assumed to be isotropic –S/B ~ 6.8  Simulation/digitization/reconstruction:  Identical to signal  Analysis  Same analysis code run over background to calculate acceptance

16. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  16/19 Normalised Maximum Likelihood Estimator Tagging efficiency. B-tag: ε tag1 = 1 – w; ε tag2 = w (Anti B)-tag: ε tag1 = w; ε tag2 = 1 – w No tag: ε tag1 = ε tag2 = 0.5 Convolution with Gaussian to account for proper decay time resolution Reconstruction efficiency and acceptance corrections: determined from simulation Background (level determined from simulation) Theoretical PDF: W + for B 0 at production W - for anti-B 0 at production

17. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  17/19 Maximum Likelihood test results X S fixed: can be determined with B s →D s π Uncertainties on  s are a function of X s ГsГs ΔΓ s δ1δ1 δ2δ2 ГsГs 70% ΔΓ s δ1δ1 98% δ2δ2 σ(  Bs )=85fs ΔГ s  =0.1 ΔΓs12% Γs0.7% A║A║ 0.8% A┴A┴ 3%  s (X s = 20) 0.03  s (X s = 40) 0.05 Uncertainties: Correlations:

18. R.W.L.Jones High Precision Measurements of B s Parameters in B s  J/  18/19 Conclusion: Estimated reach of ATLAS No sensitivity to Standard Model values –(nor have LHCb or CMS) CDF recently made a unexpectedly large measurement of ΔΓ s /Γ s Study of this “Golden Channel” in ATLAS should provide a rich yield of interesting data