Signal-background Interference Effect On Higgs Production With Four Fermions Final States At CEPC

After the discovery of Higgs particle,the Standard Model is basically complete.In order to further verify the standard model and explore new physical phenomena beyond the Standard Model,the next important task is to measure the parameters of Higgs particles(such as mass,width,decay modes and their branching ratio,the scattering cross sections of various production processes)precisely using high-energy colliders.At same time,more accurate calculations of the properties of Higgs particle is required.Along with the improvement of measurement precision,the interference terms between background and signal process(i.e.signal-background interference effect)in Higgs production may be not to be ignored.In addition,the signal-background interference effect can also affect the measurement of Higgs mass and width.Therefore it is of great significance to study the contribution of this part on the theoretical aspect.Circular Electron Positron Collider(CEPC)was proposed by Chinese physicists in 2012.CEPC as a Higgs factory will make import contributions to the precise measurement of Higgs properties till it would be built.The gold channel to product Higgs boson is Higgsstrahlung process which is the process of Higgs production associated with Z boson.Then the Higgs and Z bosons decay to the corresponding final state.Generally,Z bosons is reconstructed through the decay mode of μ~+μ~-.Decays to fermion pair is the main decay mode in all decay patterns of Higgs particle when the Higgs mass is set to 125 GeV.Among the decay mode of fermion pair,b(?) decay mode is most important and its branch ratio is 56%,and τ~+τ~- is secondary important mode with a branch ratio of 6%.In this paper,the production of four fermions final states at the CEPC is studied,and the signal-background interference effects of e~+e~-→H(b(?)/τ~+τ~-)Z(μ~+μ~-)process are investigated.For the process of e~+e~-→H(b(?))Z(μ~+μ~-),when the width of the Higgs particle is set to 4.2 MeV which is just the value in the Standard Model,the peak value of the differential cross section of the signal process which produce Higgs boson is 10~3 fb/GeV in the b(?) invariant mass spectrum.For the e~+~e-→H(τ~+τ~-)Z(μ~+μ~-)process,the peak value of the differential cross section of the signal process is 10~2 fb/GeV in the τ~+τ~- invariant mass spectrum.In the on-shell region,the signal-background interference contribution is of the order of 1/1000 of the cross sections for the two processes,below the measurement accuracy of the present experimental design.In addition,there is great uncertainty for Higgs width in the predictions of some new physics models beyond the Standard Model.The effects on the cross sections for selecting different values of the Higgs widths are also studied.