Research On The Lepton Number Violating Decays Induced By Majorana Neutrino

Neutrino oscillations have evidenced that the neutrino is not massless.Determining whether the neutrino is a Dirac particle or a Majorana one is the basis to study the neutrino mass origin,the neutrino mixing,and even interactions of elementary particles.So,clari-fying its essential attribute is the core of the neutrino research for some time now.If it is a Dirac Fermion,the neutrino and anti-neutrino are two different particles which cannot cause lepton number violating(LNV)processes.If it is a Majorana Fermion,the neutrino and anti-neutrino are the same particle which is able to induce the process with lepton number violation by two units(| △L| = 2).Thus,the existence of | △L| = 2 process is the key proof to determine the nature of neutrino.Currently,the three-body decays are the main concerns of theoretical and experimental researches,however there lacks study of heavy mesons and τ four-body decay processes,which is more hopeful to be the break through:the heavy meson’s yields are high,and their four-body decays have the same magnitudes of branching ratios as the corresponding three-body ones;while τ four-body decay has the | △L| = 2 phenomenon,which does not exist in its three-body process.As a result,it presents to be rather necessary to study the heavy mesons and τ four-body LNV decays.We study B and D meson LNV(lepton flavour violating,LF V)four-body processes,resolve the related hadronic matrices using pseudoscalar meson wave function constructed by Bethe-Salpeter method based on the potential model under the instantaneous approxi-mation,obtain the transition amplitude of LNV parts with the charged current Lagrangian of massive neutrino,calculate four-body phase space integration with Monte Carlo ran-dom numerical method,show the dependencies between branching fractions and Maj orana neutrino masses of these processes,and analyze the piecewise phenomenon of branching ratio curves in different neutrino mass range deeply.Considering the experimental ini-tial heavy meson yield and final particle detecting efficiency,the reconstruction events of some channels with large branching ratios are estimated,to study the possibility of confirming the Majorana neutrino by searching these decays.Firstly we calculate three-body meson LNV decays M →M1l1l2 under the condi-tion that they share the same mixing parameters with four-body cases.Combining their experimental branching ratio upper limits to redefine excluded region of mixing param-eters.Then the renewed parameters are applied on studying four-body LNV processes from B meson to a vector meson:B→D*l2l2M2,and calculating the dependencies be-tween their branching fractions and Majorana neutrino mass,where related vector meson wave function in the hadronic matrix is derived from the instantaneous Salpeter equation in initial particle rest frame.We also analyze the influence of branching ratios caused by mixing parameters in different neutrino mass range,and discuss which four-body LNV processes of heavy meson B to ascertain the nature of Majorana neutrino.We compare the LNV process τ+→e+e+π-υτ induced only by a Majorana neutrino and LFV process τ+→e+e+π-υe which could be induced by either a Majorana neutrino or a Dirac one.It is impossible to distinguish these two processes only through their prod-ucts,since the Standard Model neutrino in the final state is difficult to detect.Accordingly,we calculate their π spectrum of differential branching ratios in τ rest frame to explain the discrepancy of the two cases.To exclude the effect brought by mixing parameters between heavy neutrino and charged leptons,π spectrmm of normalized differential branching ra-tios are calculated as well,and the possibility to differentiate Majorana neutrino and Dirac neutrino in the rang of mπ<mN<mτ is also demonstrated considering the upgrade of future experiments.