Linear Collider Four-body Final State Process The Qcd Correction

Although the Standard Model(SM)has got a great success,it still has many theoretical problems,such as the hierarchy problem.We believe that the SM is only a lower energy approximation of a more basic theory.Unfortunately,the Higgs boson,which gives masses to gauge bosons and fermions in the SM,has not been directly observed in experiment until now.The solution of these problems requires the future experiments operated in the machines with more higher colliding energy.The future International Linear Collider (ILC)is designed as a TeV scale collider machine operating with electron-positron, photon-photon,electron-photon colliding modes.Compared with the Large Hardron Collider (LHC),it can provide much more clean signals.Therefore,it is possible to probe the SM theory in high precision and search for new physics by using the ILC.Since the Higgs boson has not yet been discovered by now,one of the most important physics goal at the ILC is to directly discover the Higgs boson.The study of top physics is another important task at the ILC,since the phenomena involving top quark is sensitive to the new physics due to its huge mass.In this thesis,I present the study the processes of t(?)b(?)and W+W-b(?)production at ILC.The t(?)b(?)production events contains the signals and background of the t(?)H production process,which is important for probing Yukawa coupling.The W+W-b(?)production process includes the HZ,t(?)-pair production events and their backgrounds.Both the HZ,t(?)-pair production processes are all important for the research of the Higgs physics and the top physics.Our calculations of these two processes are implemented up to QCD next-to-leading order.The main innovations in this thesis are listed below:●In the very high collision energy,many physical processes at the future colliders have large s-channel suppression effect.Their main contributions are always from t- or u-channel.As we know,the general Monte Carlo program for four-body phase space integral,which is implemented by repeatedly factorizing four-body phase space as several two-body phase spaces,works well for process dominated by schannel, but is not efficient for the process donainated by t- or u-channel.For the later case,we create a new four-body space Monte Carlo integral method to calculate process dominated by t- or u-channel. ●Scalar and tensor 6-point integral functions are present during our calculations of complete NLO corrections for the processes with tour final particles.Before our works,only A.Denner et al.had provided the calculations involving only the tensor 6-point integral functions up to three-rank.We extend their expressions to four-rank tensor integral functions and use another method to derive the scalar and tensor 6-point functions up to four-rank independently.We have done cross check by using both two expressions,and got a good agreement.Finally,we combine both methods to create program codes for calculating the complete scalar and tensor(up to fourrank) 6-point integral functions in different phase space regions.●In calculating of the processes with final multi-particles(n＞2),people always suffer from the trouble due to unstable particle(resonance).There are some traditional methods to deal with the resonance problem,such as effective theory,narrow-width approximation and etc.Since these methods cannot guarantee to preserve the gauge invariance,they cannot be adopted directly to the calculation for the processes up to NLO,especially when the concerned process has several resonance channels.So we use the complex mass scheme(CMS)method which can preserve the gauge invariance in the calculations up to one-loop order to deal with the resonance problem. In this work we extend the expressions for calculating one-loop integral functions to the complex mass plane according to the requirement of the CMS method and develop the program codes for calculating one-loop integrals with complex masses.