Infoscience

Thesis

Measurement of the rare radiative B Meson decays B --> [phi]K[gamma] and B --> [omega]K[gamma] at the Belle experiment and contribution to software development at the LHCb experiment

The Belle experiment is one of the world's two currently running high-energy physics detectors dedicated to study B-mesons produced with an electron-positron collider. It is situated at the Japanese High Energy Research Organization KEK in Tsukuba, near Tokyo, Japan and has been taking data since 1999. So far over 700 millions of B B pairs have been collected, the largest number ever recorded by a single machine. In the analysis described by this report, 534.586±7.044 millions of these B-mesons pairs have been analyzed to measure with precision the branching fraction (BF) of the charged and neutral B → φKγ decays. In the charged φ mode we measure a BF of · 10-6 with a significance of 10.8, in the neutral mode we find a BF of · 10-6 with a significance of 5.5. In addition we claim a first evidence of the never observed B → ωKγ decays: in the charged decay mode, we find a BF of · 10-6 with a significance of 3.7 and in the neutral mode a BF of · 10-6 with a significance of 2.8. Combining the results in the neutral and charged ω modes we reach a significance of 4.5. Besides of the interest that these results represent, they are a further step in exploring the rare radiative b → sγ decays and provide the ground work for future CP violation studies. Indeed, b → sγ decays have regained interest lately in the quest for New Physics. Observing a large mixing-induced CP-violation could be a sign for New Physics – recent theoretical Standard Model (SM) calculations for the exclusive b → sγ mode B → K*γ have shown that it should be rather small. Thus in two year's time, when the Belle experiment, along with its competitor, the BaBar experiment in the United States, will come to an end, we will definitely be in the need of a newer generation experiment to either confirm the results found by then with greater precision or continue the search for New Physics in rare B decays and of course b-physics in general. By then, the new LHCb experiment situated at the large hadron collider LHC at CERN in Geneva, will have recorded its first events and hopefully there will also be a so-called Super-B factory as a follow-up experiment for BaBar and Belle, situated on an electron-positron particle accelerator.

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