Medicion de la masa del meson B+ en el detector CMS

This thesis present the measurement of the mass of the B+ meson produced in pp collisions at a centre-of-mass energy of √ s = 7 T eV . The data correspond to an integrated luminosity of 5.05 f b−1 collected by the CMS experiment operating at the LHC. The exclusive decay for this study is B+ → J/ΨK+, where J/Ψ meson is reconstructed via the decay mode J/Ψ → µ +µ −. Certain consideration are evaluated to obtain an acceptable measurement, such as suppress some decays, for example one track appears not reconstructed (B0 → J/ΨK+π −). In this work, we find: Mrec B+→J/ΨK+ = 5278.4 ± 0.116 MeV/c2 where the mass difference with the PDG mass, is the small value of: Mrec B+ − MP DG B+ = 0.85 ± 0.28 MeV/c2