Study Of The CP Asymmetry In ??K_S?v_? Decays

Charge-Parity(CP)violation is one of the most interesting topics in particle physics.Up to now,CP violation in weak interactions has been observed in K-,B-,and D-meson systems,and all results could be accommodated within the Standard Model(SM)by the single irreducible complex phase of the Cabibbo-Kobayashi-Maskawa(CKM)quark-mixing matrix.However,the fundamental origin of CP violation is still unclear,and the CP-violating effect arising from the CKM mechanism within the SM is too small to explain the observed matter-antimatter asym-metry of the Universe.Therefore,any further study of the origin of CP violation and search for CP-violating effects in other systems will be of great significance.In this respect,the hadronic? decays,besides serving as a clean laboratory for studying the low-energy behaviours of QCD,may also allow us to explore the CP-violating effects within the SM and beyond.In this thesis,we will perform a systematical investigation of the CP asymmetry in the decay-rate and angular distribution of ??Ks?v? decays.In chapters 2-4,we firstly introduce the basic knowledge relevant to this thesis,including the SM,CP violation,effective field theory,and dispersion relation.Then,we will focus on the main body of this thesis,which includes the following two components:Decay-rate asymmetry in ??-+Ks?v? decays In 2012,the BaBar collaboration mea-sured for the first time a nonzero decay-rate asymmetry in ??KS?v? decays,and found that there exists a 2.8 ? discrepancy between the measurement and the SM prediction for this observ-able.Motivated by such a discrepancy,we will perform in chapter 5 a detailed phenomenolog-ical study of ??KS?v? decays,focusing especially on the observed CP anomaly.Since the Ks is experimentally reconstructed by a final state ?+?-,we describe the complete processes?±?KS,L?v??[?+?-]?±v? by employing the reciprocal basis.Our prediction is consistent with the result obtained by Grossman and Nir,but still has 2.8 ? discrepancy away from the BaBar measurement.As this discrepancy may attribute to the contribution from New Physics(NP),we make an analysis of these processes both in a model-independent framework and in the scalar leptoquark model.As the K? tensor form factor plays a crucial role in generating a nonzero direct CP asymmetry that can arise only from the interference of vector and tensor oper-ators,we present for the first time a dispersive representation of this form factor,with its phase obtained in the context of chiral theory with resonances,which also warrants properties of both unitarity and analyticity.It is observed numerically that the CP anomaly can be accommodated in the model-independent framework,even at the 1? level,together with the constraint from the branching ratio of ?-?KS?-v? decay;it can be,however,marginally reconciled only at the 2 ? level,due to the specific relation between the scalar and tensor operators in the scalar lepto-quark scenario.Once the combined constraints from the branching ratio and the decay spectrum of this decay are taken into account,these two possibilities are however both excluded,even without exploiting further the stronger bounds from the(semi-)leptonic kaon decays under the assumption of lepton-flavour universality,as well as from the neutron electric dipole moment(EDM)and D0-D0 mixing under the assumption of SU(2)invariance of the weak interactions above the electroweak scale.Thus,we can explain the CP asymmetry measured by the BaBar collaboration,neither in the model-independent framework nor in the scalar leptoquark model.CP asymmetry in the angular distribution of ??KS?v? decays Inspired by the study made in chapter 5,we then point out in chapter 6 that the CP-violating effect in K0-K0 mixing can not only lead to the decay-rate asymmetry of ??KS?v? decays,but also lead to the CP asymmetry in the angular distribution of the same processes.It is pointed out,for the first time,that,once the CP violation in K0-K0 mixing is taken into account,a non-zero CP asymmetry can be observed in the angular distribution of ??KS?v? decays,even within the SM.Although being below the current Belle detection sensitivity that is of O(10-3),our predictions for this observable are expected to be detectable at the Belle ? experiment,where(?)times more sensitive results will be obtained with a 50 ab-1 data sample.