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A study of B --> ccBAR γK in the BABAR experiment Fulsom, Bryan Gregory


The BABAR Collaboration is a high energy physics experiment located at the Stanford Linear Accelerator Center. The primary goal of the experiment is to study charge and parity violation in the B-meson sector, however the copious production of B mesons decaying to other final states allows for a wide-ranging physics program. In particular, one can access the charmonium system via colour-suppressed b —> c decays of the type B —> ccBAR K. This thesis presents a study of B —> ccBAR γK decays where ccBAR includes J/ψ and ψ(2S), and K includes K±, K°s and K*(892). The particular emphasis is on a search for the radiative decays X(3872) —> J/ψγ and X(3872) —> ψ(2S)γ. The X(3872) state is a recently-discovered resonance of undetermined quark composition, speculatively a conventional charmonium state or exotic four-quark di-meson molecule. This research is also sensitive to the well-known radiative charmonium decays B —> Xcl,2K, which are used as verification for the analysis technique. This dissertation sets the best B —> Xc1K branching fraction measurements to date, and sees the first evidence for factorization-suppressed B⁰ —> Xc2K*⁰ decay at a level of 3,6σ. It also provides evidence for X(3872) J/ψγ and X(3872) —> ψ(2S)γ with 3.6σ and 3.3σ significance, respectively. The product of branching fractions B(B± X(3872)K± . B(X(3872) —> J/ψγ = (2.8 ± O.8(stat.) ± O.2(syst.)) x 10⁻⁶ and B(B± —> X(3872)K). B(X(3872) —> ψ(2S)γ )=(9.5±2.7(stat.)±0.9(syst.)) x 10⁻⁶ are measured. These results improve upon previous X(3872) —> J/ψγ measurements, and represent the first evidence for X(3872) —> ψ(2S)γ.

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