Determination of the transverse momentum distribution for the production of THDM and MSSM Higgs bosons via gluon fusion at next-to-leading order using POWHEG

Extensions of the SM like the MSSM which predict an extended Higgs sector are contemporary fields of research. In the recent search for additional neutral MSSM Higgs bosons at the LHC, theoretical predictions for physical observables have to be compared with experimental measurements. Theoretical predictions for the LHC are obtained using numerical simulations. In the case of the simulation of the production of a neutral MSSM Higgs boson via gluon fusion a non-trivial tan β dependency exists, which would lead without an efficient reweighting procedure to an overabundance of templates. The goal of this thesis was to study how the reweighting method, deduced for THDM, can be used to efficiently approximate MSSM predictions for a large variety of values of tan β and m_A at the LHC. The generation was performed using POWHEG in the THDM mode as a matrix element generator, which provides kinematic distributions at NLO plus parton shower accuracy. The reweighting method at NLO for the production of a pseudoscalar Higgs boson via gluon fusion in the THDM was explained. The precision of the calculated cross section for the production of a Higgs boson via gluon fusion at NLO QCD plus parton shower accuracy with POWHEG can be improved by treating the calculation as a multi scale problem. In the presented approach, the differential cross section for the production of a pseudoscalar Higgs boson is split into individual differential distributions from only the top-quark, only the bottom-quark and the top-bottom interference. The uncertainty due to the resummation scale dependence is reduced by up to 15% by calculating the individual contributions at different resummation scales. In addition, because of the factorization of the tan β dependent Yukawa couplings of the individual contributions, this splitting allows for an efficient reweighting to arbitrary values of tan β. It was observed that the top-bottom interference term is independent of tan β. The statistical uncertainty for the determination of the interference term was reduced by the choice of an ideal reference point on tan β. The reweighting method for the combination of the individual contributions to the full differential cross section for arbitrary values of tan β was found to be suitable for the THDM at NLO. For the production of a heavy scalar Higgs boson, an additional input parameter, the mixing angle α, has to be taken into account by the reweighting procedure. This is reflected in the corresponding α dependent Yukawa couplings of the top- and bottom-quark to the heavy scalar Higgs boson. The reweighting method for an arbitrary value of tan β and α was found to be applicable in case of the THDM NLO heavy scalar Higgs boson production. The optimization to find the ideal reference point for the calculation of the interference term in the case of the heavy scalar Higgs boson is a three dimensional problem {m_H, tan β, α}. However, the described procedure is analogously applicable. Then the transfer from the THDM to the MSSM was made. An approximation for the MSSM (aMSSM) can be obtained where higher order SUSY corrections are applied in form of a modification of the Yukawa couplings of the THDM, leading to effective Yukawa couplings. It is found that the factorization of the Δ_b corrections leads to an effective Yukawa coupling of the aMSSM which is up to 15% lower relative to the Yukawa coupling of the THDM. Squark contributions beyond Δ_b are neglected by the proposed method. The impact of these non-considered SUSY corrections is determined by a comparison of the aMSSM and the full MSSM calculation for a given reference point in m_A and tan β. It is found to be be below 5%. A first application of the reweighting method presented in this thesis has been performed in the recent search for additional neutral MSSM Higgs bosons in the di-tau final state in proton-proton collisions at √(s)=13 TeV. The result of the expected and observed upper limit calculation of a single narrow resonance for the production of a neutral MSSM Higgs boson is shown. The limits are obtained using the data of proton-proton collisions corresponding an integrated luminosity of 35 fb^-1. In this analysis a sensitivity to the Higgs boson p_T spectrum is only observed for the low mass region. Consequently the reweighting method presented in this thesis has no large impact in this analysis. However, for future MSSM H→ττ analyses the Higgs boson p_T is an important observable for improving the sensitivity. For these analyses the reweighting method presented in this thesis will be important to improve the signal prediction and to reduce the uncertainty on this prediction.