Study Of W-pair And Higgs-pair Productions Associated With Jet At LHC

With the discovery of the Higgs boson at the CERN Large Hadron Collider (LHC) by ATLAS and CMS collaborations in July 2012, the standard model (SM) becomes complete and one of the most successful theories in the history of particle physics. The current experiments indicate that the properties of the new discovered particle are roughly compatible with the SM Higgs boson. But to identify whether this particle is the SM Higgs boson or new physics model Higgs boson, and further deeply understand the electroweak symmetry breaking (EWSB), more precise tests are quite essential. For fulfillment of precise tests, firstly, precise theoretical prediction should be made in-cluding the signals and backgrounds of Higgs productions. Moreover, precise test of the coupling of the vector bosons is also very important for understanding the EWSB. Furthermore, precise tests should also include the study of the self-coupling of Higgs bosons and the Higgs potential, thus the study of Higgs pair production processes are very necessary. Finally, although SM has achieved giant success, SM is not the ultimate theory of physics, thus, the new physics models should be also investigated.To the precise test of the coupling of the W-bosons, we investigate the next-to-leading order (NLO) EW and QCD corrections of process pp â†' W+W-+jet+X with spin-entangled decay of W-boson at the LHC. Since the precision measurements will be possible at the LHC Run 2, the high collider energy and enormous luminosity are permitted to produce gauge bosons with large transverse momentum up to TeV scale, the NLO EW corrections become very important due to the EW Sudakov effect. In the year of 2013, the international conference of high energy physics hold at Les Houches emphasized the urgent need of the NLO EW and QCD corrections of vector boson pair associated with jet production processes. In this thesis, we investigated the dependence of the leading order (LO) and NLO corrected cross sections on the transverse momentum cut of leading jet. In dealing with the subsequent resonant W-boson decays, we adopt the MadSpin method to include the spin correlation effect of W-boson decay. At last, we also provide the LO and NLO corrected distributions of the transverse momenta and rapidities of final products. The results show that the NLO EW correction is very significant in the high transverse momentum regions.To study the self-coupling of Higgs bosons, we studied the next-to-next-to-leading order (NNLO) QCD corrections to the vector boson fusion (VBF) process ppâ†'h0h0+ 2jets+X in the type â…¡ of the two Higgs doublet model (2HDM). In the SM, Higgs pair production via VBF has the second largest cross section and offers a clean ex-perimental signature of two centrally produced Higgs bosons with two hard jets in the forward/backward rapidity region. Thus, this process can be used to investigate the Higgs self-coupling and reconstruct the Higgs potential. Due to the importance men-tioned above, precise study of this process is quite necessary. We adopt the well-known structure function approach calculating the NNLO QCD corrections. At first, we in-vestigate the model parameter dependence, residual uncertainties from the factoriza-tion/renormalization scale, PDFs and αs on the integrated cross section, and find that the NNLO QCD corrections can reduce the scale uncertainty significantly. Then we present the kinematic distributions of final Higgs bosons, which can be used to study the Higgs self-coupling (λH0H0h0 andλh0h0h0).In summary, the innovations of this thesis are listed as follows:· We present the full NLO EW corrections of the process ppâ†'W+W-+jet+X with spin-entangled decay of W-boson at the LHC for the first time, and give the NLO QCD+EW corrections which by far are the most precise theoretical predic-tions. In the calculation, we reduce the amount of calculation greatly using the unitarity of the CKM matrix. We also checked the EW Sudakov effects by chang-ing jet transverse momentum cut. When dealing with the decay of W-boson, we use the MadSpin method to include the spin correlation effect of W-boson decay.· In dealing with the one loop tensor integrals of the process ppâ†'WW+jet+X, the numerical instability problem will arise when the small Gram determinant occurs. To solve this problem, we developed the double and quadruple preci-sion computer program packages which significantly improve our calculating ef-ficiency. For the real photon radiation part, the W+W-+jet+γ four-particle events are involved, we use an accurate event selection rule to distinguish the jet/photon event, and creatively use the quark-to-photon fragmentation solving the infrared divergence problem.· By adopting the structure function approach, we present the NNLO QCD correc-tions of VBF process ppâ†'h0h0+2j ets+X in 2HDM type â…¡ for the first time. The scale uncertainties of this process are significantly reduced by the NNLO QCD correction. Besides, our codes is efficient and flexible, and can be used to calculate n-body Higgs particles production via VBF in the SM and 2HDM.