Study On The Decay Of J/???f₁(1285),?f₁(1420)

With the development of high energy physics,people can have a deeper understanding of the micro world by studying the properties,motion and interaction of particles.Among the unflavored light mesons listed in the Particle Data Group(PDG),there are abundant light axial vector mesons with a spin-parity quantum number JP=1+,including the f1(1285)and f1(1420)states which are studied in this thesis.Although they have been observed in experiments for a long time,their properties and structure are still controversial.The f1(1285)state is considered to be a conventional qq meson or a hadron molecular state,etc.The particularity of the f1(1420)state is that it is only seen in the KK? and KK*+c.c.decay modes.Recently,it has been found that the peak at 1420 MeV seen in the invariant KK? mass spectrum is the manifestation of the K*K and a0(980)? decay modes of the f1(1285)resonance,and then the "f1(1420)" is not a real resonance.This inspires us to make a further study of the f1(1285)and f1(1420)states,with the hope to reveal their properties from a new perspective.In this thesis,basing on the the lowest order chiral Lagrangian of vector meson(V)pseudoscalar meson(P)interaction,the axial vector meson with quantum numbers IG(JPC)=0+(1++)is studied by VP s-wave scattering under the framework of chiral unitary approach(CHUA).The scattering T matrix can be obtained by solving the BS equation,where the three-momentum cutoff renormalization and the dimensional regularization are used respectively to deal with the divergent loop function of the meson-meson propagators,and the width of vector meson is taken into account in the loop function.When taking the cutoff parameter as qmax=1000 MeV,the T matrix has a pole of 1281.2-4.6 MeV,with its mass,width and quantum numbers being consistent with the light axial vector meson f1(1285).This dynamically generated state couples mainly to K*K+c.c.,and its mass is below the K*K threshold.Therefore,the axial vector meson f1(1285)is considered to be a K*K+c.c.molecular state generated from the VP s-wave interaction.With the molecular picture of the f1(1285)state,the reaction mechanism,decay amplitude,decay width and the invariant mass spectrum of the J/???f1(1285),J/???K*K+c.c.and J/???K0?+K-decays are further studied in this thesis.The vertex structure of J/?VP is analyzed basing on the spin-parity conservation and SU(3)symmetry,and the expressions of amplitude and decay width of the J/???f1(1285)and J/???K*K+c.c.decays are obtained.These two decay processes contain the same bare coupling constant VP for the J/??K*K vertex.The factor VP can be cancelled by defining the ratio R?=(dFJ/???K*K/dMinv)/?J/???fl(1285),and the shape of R? as a function of the invariant mass Minv of the K*K(or f1(1285))system is predicted.Since R?does not contain any free parameters,the theoretical prediction of R? in this thesis provides a valuable reference for the experimental measurements of the J/???f1(1285)decay and the J/???K*K+c.c.decay in the future,being helpful to test further the molecular picture of the f1(1285)state.On the basis of the above research,taking into account that the vector meson K*or K*decays into K? or K?,the decay process o1 J/???+c.c.??K0?+K-is studied in detail.The tree-level Feynman diagram without f1(1285)contribution and the loop-level Feynman diagram with f1(1285)contribution are obtained,and the corresponding amplitudes and partial decay widths are calculated.The double-peak structure is observed in the invariant mass spectrum of K0?+K-.The first peak corresponds to the f1(1285)state dynamically generated in the process of J/???K0?+K-.The second peak corresponds to a mass of about 1420 MeV and a width of about 60 MeV,which accords with the experimental conditions of f1(1420).However,no parameters or information about the f1(1420)state are added in this study.Although f1(1420)has been observed in more than 20 experiments and has been recorded as a standard resonance state by PDG,the experimental observation of this state is basically a peak in the KK? invariant mass spectrum,and there is still much controversy about the decay properties of f1(1420)state.Therefore,the results of our study show that the peak at 1420 MeV in the KK? invariant mass spectrum is due to the kinematic effect of the f1(1285)decaying into K*K+c.c.in higher energy region,saying that the "f1(1420)" observed in experiment is not a real resonance state.This provides a new perspective for further confirmation and study of f1(1420).