Physics analysis of the Belle experimental data

Belle is an experiment at the Japanese center for particle physics KEK, operated by an international collaboration of about 400 scientists. It studies the decays of short-lived B mesons (lifetime 1.6 picoseconds) produced in electron positron collisions at the energy of 10.58 GeV. The aim of the experiment is to probe the theory of the Japanese physicists Makoto Kobayashi and Toshihide Maskawa who explained CP violation (differences between particles and anti-particles) through mixing of the quark flavor eigenstates. By studying more than 700 million B pair events, Belle could actually confirm their hypothesis and thus play a strong supporting in their 2008 physics Nobel prize. However, that`s not all we can learn from B meson decays: In the present phase of the experiment and with the Belle-II upgrade, we aim at probing this so-called CKM mechanism with even higher precision. Deviations from the CKM picture would hint at physics beyond the Standard Model of particle physics. If there are new, heavy particles in the TeV-range, their effect must also be seen in B decays. This FWF project should be seen in the context of this experimental program: We propose to determine the CKM matrix element |Vcb| using the decay B ` Dl and to measure the decays Bs ` J/ and Bs ` J/ KS. We apply for funding for two Ph.D. students for a duration of 36 months. This time will be sufficient to bring the two aforementioned physics analyses to a level that allows journal publication of the results. We also apply for travel expenses to allow the students to participate in one collaboration meeting at KEK per year.

While equal amounts of matter and anti-matter were created during the Big Bang, the Universe today seems to be composed exclusively of matter. In fact, during the creation of the Universe just a little bit more matter than anti-matter was produced and remains today. For this to happen on a fundamental scale, particles must behave slightly differently than their mirror partners, the anti-particles. This is what particle physicists call CP violation. The only known source of CP violation in particle physics is the Kobayashi-Maskawa phase, which appears in transitions of quarks, the fundamental constituents of matter in the Standard Model of particle physics. This so-called Cabibbo-Kobayashi-Maskawa (CKM) mechanism is precisely the research topic of the Belle experiment, located at the Japanese laboratory for particle physics KEK. In this experiment about 300 researchers from around the world study transitions of massive and very short-lived particles produced in electron-positrons collisions to prove or disprove CKM. The research carried out within this FWF project contributes to the analysis of the Belle data in this international framework. While our measurements bring the test of CKM to a new level of precision, they also confirm the description of fundamental physics in terms of the Standard Model.