The Study On Light Invisible Particles Generation And Lepton-Number Violation In Rare Decays Of Heavy Mesons

The Standard Model is the most successful theory in Particle Physics,and has been extensively verified in experiments.However,the Standard Model is considered to be an effective theory that only takes effect under low energy scale.And it is generally believed that there are new physics beyond the Standard Model.The existence of dark matter was first discovered in cosmological observations,and the mass proportion of dark matter in Universe is even much higher than that of normal matter.But from the point of view of Particle Physics,the Standard Model cannot provide reasonable candidates for dark matter.In addition,one of the explanations for the asymmetry of matter-antimatter in the evolution of Universe is to realize the asymmetry of the baryon number through the nonconservation of the lepton number.However,physical processes involving lepton-number violation are also not allowed in the Standard Model.This dissertation mainly studies the new physical phenomena that may exist in the rare decay processes of heavy mesons.The upper limits of the branching ratios of missing energy phenomenon in the rare decay processes of heavy mesons are given experimentally,The experimental upper limit currently obtained is larger than the theoretical prediction of the Standard Model neutrinos.We explain this anomaly by introducing new invisible particles,and consider that new invisible particles may be candidates for dark matter.Specifically,we select the flavor-changing neutral current processes M-→Mf*-+E of B-and Bc-meson,and the annihilation process B0(D0)→E of B0 and D0 meson.M-→Mf*-+vv and B0(D0)vv processes are their Standard Model background.The difference between them leaves room for the existence of new physics.We discusses the production of paired invisible(pseudo)scalar,paired invisible spinors(including Majorana and Dirac types)and single invisible scalar or vector in these processes.By introducing the phenomenological dimension-five or dimension-six effective Lagrangian operator,the coupling between the new particles and the Standard Model quarks is described.In order to make this work more general,the introduced operator includes all possible coupling forms.The Feynman amplitudes are written according to the Feynman diagrams.By finishing the phase space integral of the square of amplitude,the decay width are obtained.Compared with the experimental upper limits of branching ratios of B meson,we obtain the upper limits of coupling constants.Within the freeze-in mechanism and combined with specific model,the observation results of the relic density of dark matter can give the lower limits of the coupling constants.These limits are applied to corresponding decay processes of Bc meson.The allowed range of branching ratios of Bc meson decay processes with invisible particles is given,where the upper limits are about BR[Bc→Mf(*)χ(χχ)]<10-5～10-6.In the specific calculations,the form factors of the hadronic transition matrix element are obtained by the QCD light-cone sum rules and solving the instantaneously approximated Bethe-Salpeter equation.In addition,we also study the four-body decay processes of neutral flavored mesons,including K0,D0,B0,and Bs0.These processes,which induced by a hypothetical doublycharged scalar particle,violate the lepton number.The quantity BR×(sΔhij/mΔ2]-2 of different channels are calculated,where sΔ,hij,and mΔ are parameters related to the doubly-charged scalar.For K0→h1+h2+l1-l2-,D0→h1-h2-l1+l2+,and Bd,s0→h1+h2+l1-l2-,it is of the order of 10-13～10-11 GeV4,10-17～10-10 GeV4,and 10-17～10-10 GeV4,respectively.Based on the experimental results for the D0→h1-h2-l1+l2+ channels,we also set the upper limit for(sΔhij/mΔ2).