2 The CDF Experiment at Fermilab Contents - Harvard University ...

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90 Section 2: CDF Physics Analysis Bs Ds K φ π K K Other B Decay (used for tagging) 000 111 000 111 000 111 000 111 Primary Vertex Bs Ds Fragmentation K (used for tagging) K Figure 43: Diagram of the B s ! D s K; D s ! ; ! KK decay, including fragmentation K and opposite side B used for avor tagging. Measuring sin with B s ! D s K Bailey has performed a feasibility study for measuring sin using the decay mode B s ! Ds K at CDF II. Since then, he and Maksimovic have improved this study and presented it to the collaboration. This mode is unique to hadronic colliders (the B factories do not produce B s ) and thus provides an important complement to studies using B 0 . It also has the benet of not involving \penguin" diagrams which make many CP violation measurements ambiguous through their non-CP violating contributions. With a relatively large decay rate, B s ! Ds K is one of the best decay modes for measuring sin which is necessary for the full consistency check of the Standard Model. The theoretically expected errors are inversely proportional to a variety of dilution factors which eectively reduce the amplitude of the signal observed. These dilution factors arise from measurement resolutions, backgrounds, t limitations, and avor tagging ineciencies and mistags. Using the latest CDF II estimates for these dilutions the expected error on sin is 0.45. To check the dependence of this measurement upon various input parameters, Bailey wrote a toy Monte Carlo simulation and likelihood tter including backgrounds, resolution eects, and mistag probabilities. The measurement involves an unbinned likelihood t to four dierent decay rates (both B s and B s to both D s , K + and D s + K , ) to extract the weak phase , a strong phase, and the ratio of the decay rates. The input parameters to the event generation and t were varied and the resulting error on sin was studied. It was found to scale as expected by theory. Figure 45 (left) shows the expected error as a function of the B s mixing parameter x s = m s =,. The current limit on m s is 10:2ps ,1 [26], but
Section 2: B Mixing and CP Violation 91 N(B s -> Ds - K + ) 30 25 20 15 10 5 0 0 0.2 0.4 0.6 0.8 1 proper time Figure 44: Example t to the proper time distribution of B s ! D s , K + . This distribution is t simultaneously with B s ! D s + K , , Bs ! D s , K + , and B s ! D s + K , to extract the CP violating parameter sin . Note that the actual t is an unbinned t; the binned nature of this plot is for visualization purposes only.
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1 2 The CDF Experiment at Fermilab
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36 Section 2: CDF 2.3 Run I Physics
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38 Section 2: CDF Physics Analysis
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Page 105 and 106: Section 2: CDF 105 References [1] T
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