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Extracting Specific Flavour Asymmetry: Studying CP Violation in Untagged B Mesons

This study focuses on measuring CP violation in untagged Bs mesons to probe new physics in mixing. The theory background, current status, problems, and next steps for the research are outlined, along with a summary of the findings and future directions.

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Extracting Specific Flavour Asymmetry: Studying CP Violation in Untagged B Mesons

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  1. Flavour specific asymmetry from untagged B samples Paul Szczypka

  2. Outline • Aim • Theory background • afs from untagged decays • Current Status • Problems • Next Steps • Summary

  3. Aim • Looking at semileptonic decays: • Measure CP violation in mixing from an untagged sample of Bs mesons • If the measurement is possible, then put limits on the number of events required to rule out new physics in CP mixing.

  4. Theory 1 Time evolution of system governed by Sch. Eqn. Where denotes the state of a meson produced as a Bsat time t = 0, similarly for . Off-diagonal elements and correspond to mixing.

  5. Theory 2 The leading contributions to M12 and Γ12 come from this box diagram: Γ12 dominated by tree-level decays – insensitive to new physics M12 induced by short–distance physics top quarks give dominant contribution to mixing but it is suppressed by four powers of weak coupling and two powers of |Vts| (≈ 0.04) Suspect that new physics could easily compete with SM and possibly dominate M21

  6. Basics • afs is the CP asymmetry in flavour specific B decays • SM expectation: afs ~ 2x10-5 • New physics could increase the value of afs by a factor of 200 • afsNP ~ 0.04

  7. Asymmetry from untagged decays Using: and We find: and ε initial prod asym. For: and Time integrated asymmetry is useful too:

  8. Toy MC Model 1 • Decide to use a toy Monte Carlo to study the feasibility of measuring large afs from an untagged Bs sample. • MC creates individual events (all flavour combinations). • Produce and by sorting events according to the flavour of the final state. • Attempt to extract MC parameters → perform a fit on your data.

  9. Toy MC model 2 Settings: Γ = 0.684 ps-1 ΔΓ = 0.3 ps-1; Δm = 17.5 ps-1; a = 0.005; P = 0.01

  10. Fitting to the Data • A simultaneous fit is performed on the and distributions. Fit Results (10k events): FCN= 21497.03 FROM MIGRAD STATUS=CONVERGED 369 CALLS 371 TOTAL EDM= 0.33E-05 STRATEGY= 1 ERROR MATRIX ACCURATE EXT PARAMETER STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 Gamma 0.68138 0.26567E-01 0.36203E-03 -0.64668E-01 2 Delta gamm 0.26088 0.74920E-01 0.17515E-02 -0.38640E-02 3 m_s 19.472 0.40316 0.28785E-01 0.54900E-02 4 Prod asymm 0.40366E-01 0.49775E-01 0.29814E-02 -0.13623E-01 5 CP mixing 0.48716E-02 0.27917E-01 0.16732E-02 0.20190E-01 Γ = 0.684 ps-1; ΔΓ = 0.3 ps-1; Δm = 17.5 ps-1; P = 0.01; a = 0.005

  11. Current problems: • MiGrad fails to converge for large N (1M here). FCN= 2168081. FROM MIGRAD STATUS=FAILED 570 CALLS 572 TOTAL EDM= 0.18E+03 STRATEGY=1 ERROR MATRIX UNCERTAINTY=100.0% EXT PARAMETER APPROXIMATE STEP FIRST NO. NAME VALUE ERROR SIZE DERIVATIVE 1 Gamma 0.68353 0.29223E-02 0.0000 2.2954 2 Delta gamm 0.29824 0.76030E-02 0.0000 0.65238E-01 3 m_s-5445.5 0.46437 0.0000 0.38898 4 Prod asymm 0.14443E-01 0.51768E-02 0.0000 15.521 5 CP mixing 0.69178E-02 0.27369E-02 0.0000 33.233 EXTERNAL ERROR MATRIX. NDIM= 50 NPAR= 5 ERR DEF= 1.00 0.854E-05 0.213E-04-0.259E-05-0.153E-07-0.282E-08 0.213E-04 0.578E-04-0.740E-05-0.364E-07-0.304E-08 -0.259E-05-0.740E-05 0.216E+00-0.176E-04 0.497E-04 -0.153E-07-0.364E-07-0.176E-04 0.268E-04 0.733E-05 -0.282E-08-0.304E-08 0.497E-04 0.733E-05 0.749E-05 ERR MATRIX APPROXIMATE PARAMETER CORRELATION COEFFICIENTS NO. GLOBAL 1 2 3 4 5 1 0.95732 1.000 0.957-0.002-0.001 0.000 2 0.95732 0.957 1.000-0.002-0.001 0.000 3 0.05070 -0.002-0.002 1.000-0.007 0.039 4 0.51825 -0.001-0.001-0.007 1.000 0.518 5 0.51929 0.000 0.000 0.039 0.518 1.000

  12. Next steps • Understand fit behaviour • Put limits on the number of events required to see new physics for this measurement. • Add detector efficiencies, e.g. time resolution of channels Example proper time resolution (CDF): <σ> = 44.6 μm/c → proper time resolution ~0.15 ps (Not great – ocsillation freq. = 0.36 ps)

  13. Summary • afs can be extracted from a sample of untagged Bs mesons in two ways: • time dependant: fit to data • time independent: simple counting of decay states • Need to understand the fitting behaviour. • Add proper time resolution (smearing) to MC data. • Work is ongoing.

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