A search for B$$0\atop{S}$$ oscillations at the Tevatron collider experiment D0
- Indiana Univ., Bloomington, IN (United States)
We present a search for B$$0\atop{S}$$ oscillations using semileptonic BS → DsμX (Ds → K$$0\atop{S}$$K). The data were collected using the D0 detector from events produced in √s = 1.96 TeV proton-antiproton collisions at the Fermilab Tevatron. The Tevatron is currently the only place in the world that produces B$$0\atop{S}$$ mesons and will be until early 2008 when the Large Hadron Collider begins operating at CERN. One of the vital ingredients for the search for B s oscillations is the determination of the flavor of the B$$0\atop{S}$$ candidate (B$$0\atop{S}$$ or $$\bar{B}$$$$0\atop{S}$$ ) at the time of its production, called initial state flavor tagging. We develop an likelihood based initial state flavor tagger that uses objects on the side of the event opposite to the reconstructed B meson candidate. To improve the performance of this flavor tagger, we have made it multidimensional so that it takes correlations between discriminants into account. This tagging is then certified by applying it to sample of semimuonic B(0,+) decays and measuring the well-known oscillation frequency Δmd. We obtain Δmd = 0.486 ± 0.021 ps-1, consistent with the world average. The tagging performance is characterized by the effective efficiency, ϵD2 = (1.90 ± 0.41)%. We then turn to the search for B$$0\atop{S}$$ oscillations in the above-named channel. A special two-dimensional mass fitting procedure is developed to separate kinematic reflections from signal events. Using this mass fitting procedure in an unbinned likelihood framework, we obtain a 95% C.L. of Δms > 1.10 ps-1 and a sensitivity of 1.92 ps-1. This result is combined with other analyzed B$$0\atop{S}$$ decay channels at D0 to obtain a combined 95% C.L. of Δms > 14.9 ps-1 and a sensitivity of 16.5 ps-1. The corresponding log likelihood scan has a preferred value of Δms = 19 ps-1 with a 90% confidence level interval of 17 < Δms < 21 ps-1, assuming Gaussian uncertainties. A comparison of the change in the likelihood between Δmss = 19 ps-1 and Δms = ∞ yields an 8% expectation for a background fluctuation.
- Research Organization:
- Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-07CH11359
- OSTI ID:
- 918719
- Report Number(s):
- FERMILAB-THESIS-2007-23; TRN: US0805896
- Country of Publication:
- United States
- Language:
- English
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