Study of orbitally excited B_(s) mesons and evidence for a new Bπ resonance with the CDF II detector

In this thesis, the study of excited B⁰, B⁺ and B_s⁰ mesons is presented, providing a test for predictions made by quantum chromodynamics. Data corresponding to an integrated luminosity of 9.6 fb^-1 of proton-antiproton collisions at the Tevatron recorded by the CDF II detector are analyzed. Excited B⁰ mesons are reconstructed in the decays to B^*+π^- and B⁺π^- combinations, B⁺ mesons in the decays to B^*0π⁺ and B⁰π⁺ combinations, and B_s⁰ mesons in the decays to B^*+K^- and B⁺K^- combinations. The Q-value spectrum of candidates for excited B_s⁰ mesons shows three peaks, interpreted as the three allowed transitions of the two narrow orbitally excited states B⁰_s1 and B_s2^*0. The same structure is assumed for the signal in the Q-value spectra of B⁰ and B⁺-mesons candidates, where at higher masses an excess over the expected background is observed for the first time. It is interpreted as a new Bπ resonance, which could be a radial or orbital excitation of a B meson. It is therefore called B(5970). The presented results include the most precise determination of the properties of the narrow orbitally excited B⁰-meson states, the first measurement of orbitally excited B^**+ mesons and first evidence for the B(5970) resonance, as well as the measurement of its properties. For each of the three investigated flavors of B_(s) mesons, the mass and width is determined for the orbitally excited B₁ and B₂^* state, as well as the relative production rate r_prod of the B₁ state to the B₂^* state. For excited B⁰ and B⁺ mesons, first evidence with 4.4σ is found for the new B(5970) resonance, its mass and width are measured and the relative production rate r_prod^' to the reaction B₂^* → Bπ is determined. The results are summarized in Table 9.1. The relative branching fraction of the two B_s2^*0 decays is measured to be (B(B_s2^*0→B^*+K^-))/(B(B_s2^*0→B⁺K^-))=0.10^+0.03_-0.02(sta t)±0.02(syst). The combined production rate of the B₁⁰ and B₂^*0 states relative to the B⁺ meson is determined to be 19±2(stat)±4(syst) %. The presented results have been published in the article: T. Aaltonen et al. (CDF-Kollaboration), ''Study of orbitally excited B mesons and evidence for a new Bπ resonance'', Physical Review D 90, 012013 (2014).