Precise Study On The Higgs Self-coupling At Hadron Colliders

On July 4th, 2012, both the ATLAS and CMS collaboration at the Large Hadron Collider (LHC) announced the observation of a new boson. The properties of the new boson are, so far, compatible with the Higgs boson predicted by the Standard Model(SM). In order to determine whether this new boson is indeed the SM Higgs boson, we must know its properties like parity, spin and couplings. Although the SM has been extraordinarily successful in describing the data of all high energy experiments, a num-ber of outstanding problems remain. Various new physics models, such as the Minimal Supersymmetry Standard Model (MSSM), the two Higgs Doublet Model (2HDM), are raised to solve the fundamental problems in the SM. The probing of Higgs couplings may give hints of new physics beyond SM (BSM). The Higgs self-couplings are ex-tremely significant for understanding the electroweak symmetry breaking (EWSB) and are indispensable to reconstruct the Higgs potential. To understand the triple Higgs self-coupling, the only accessible process is Higgs pair production.At the LHC, there are four main Higgs pair production channels: gluon-gluon fusion (GGF) gg→HH, vector boson fusion (VBF) q1q2 → V*V*q3q4→ HHq3q4,top-quark pair associated Higgs boson pair production gg/q1q2→ ttHH and double Higgs-strahlung q1q2→ VHH. In the SM, Higgs pair production via VBF provides the second largest cross section and offers a clean experimental signature of two centrally produced Higgs bosons and two hard jets in the forward/backward rapidity region. The VBF channel is a cornerstone in the detection of the Higgs pair production, and it is also sensitive to the VHH and VVHH (V = W, Z) interactions.We investigated in detail the Higgs pair production via VBF at the √S=14, 33 and 100 TeV hadron colliders within the SM and the 2HDM. Precise knowledge of the Higgs pair production process is an essential prerequisite for the experimental research.For the hadron collider physics, precision prediction needs to include higher-order QCD corrections such as QCD next-to-next-to-leading-order (NNLO). And we calculate the VBF Higgs pair production process in the SM and the 2HDM up to the QCD NNLO by adopting the structure function approach (SFA). We studied the scale uncertainty, PDF uncertainty and αs uncertainty of the QCD NNLO corrected total cross section. We find that the QCD NNLO corrections are important in improving the scale uncertainty.We also studied the sensitivity of the total cross section to the triple Higgs self-coupling strength. The numerical results show that the total cross section is strongly dependent on the strength of the triple Higgs self-coupling. We provide the distributions of the transverse momentum, rapidity, invariant mass, as well as the azimuthal angle separa-tion of the final two Higgs bosons.Since no new particle BSM has been observed and we do not know the specific form of the BSM theory, we adopt the effective field theory (EFT) approach to study the new physics. The EFT approach provides a model-independent way to investigate the new physics, the possible leading new physics effect can be generally parametrized by gauge-invariant dimension-six operators. We investigate the influences of the rel-evant dimension-six operators on the Higgs pair production via VBF at the √S=13 and 14 TeV LHC up to the QCD next-to-leading-order (NLO). The numerical results show that the integrated cross section is particularly sensitive to the operators OΦ,2 and OΦ,3, and the operators OBB and Oww have less influence on the process of VBF Higgs pair production. Then we analyze the influences of OΦ,2 and OΦ,3 on the shapes of the kinematic distributions of the final two Higgs bosons. We find that both OΦ,2 and OΦ,3 can induce noticeable changes on the shapes of the distributions of invariant mass, transverse momentum and rapidity. The different distribution shapes are helpful in distinguishing the signature of the new physics from the SM background. The 5a discovery and 3σ exclusion limits for the effects of OΦ,2 and OΦ,3 by measuring the VBF pp → HH + X → bbbb + X process are also discussed.The innovations in this thesis are listed as follows:·For the first time, we apply the SFA to the calculation of the VBF Higgs pair production process and systematically analyze this process up to the QCD NNLO.We discussed the scale uncertainty, PDF uncertainty and as uncertainty of the QCD NNLO corrected total cross section. The numerical results show that the scale uncertainty can be reduced significantly by the QCD NNLO corrections.Our publication "Phys. Rev. D89, 073001 (2014)" has drawn attention of particle physicists and has been cited more than 20 times by others until now.·In the calculation of the VBF Higgs pair production process, we also consider the√S=33 and 100 TeV hadron colliders. The total cross section increases remark-ably as the increment of √S, and the future hadron-hadron collider with colliding energy of 100 TeV is useful to probe the triple Higgs self-coupling.·We presented the effects of the dimension-six effective operators on the Higgs pair production via VBF up to the QCD NLO. We find that the effective operator OΦ,2and OΦ,3 have obvious influence on both the integrated cross section and the kinematic distributions of the final two Higgs bosons.