arXiv subjects
Publications and source records attributed to Le Duc Ninh.
We present a summary of the first calculation of NLO QCD corrections to WZjj production with leptonic decays at the LHC. Our results show that the next-to-leading order corrections reduce significantly the scale uncertainties.
Electroweak gauge boson pair production is a very important process at the LHC as it probes the non-abelian structure of electroweak interactions and is a background process for many searches. We present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model, including both QCD and electroweak corrections. The hierarchy between the ZZ, WW and WZ channels, observed in the transverse momentum distributions, will be analyzed. We will also present a comparison with experimental data for the total cross sections including a study of the theoretical uncertainties.
The dominant contribution to $H^- t\bar{b}$ production at the LHC is the gluon-gluon fusion parton subprocess. We perform for the case of the complex MSSM a complete calculation of the NLO electroweak contributions to this channel. The other small contributions with quarks or photon in the initial state are calculated at tree level. The results are improved by using the effective bottom-Higgs couplings to resum the leading radiative corrections. We find that, beyond these leading corrections, the NLO electroweak contributions can be still be significant. The effect of the complex phases of the soft-breaking parameters is found to be sizable.
We report on the calculation of $W^\pm Zjj$ production with leptonic decays at hadron-hadron colliders at next-to-leading order in QCD. These processes are important both to test the quartic gauge couplings of the Standard Model and because they constitute relevant backgrounds to beyond standard model physics searches. Our results show that the next-to-leading order corrections reduce significantly the scale uncertainties and have a non-trivial phase space dependence.
The dominant contributions to W-+ H+- production at the LHC are the tree-level b anti-b annihilation and the gg fusion. We perform for the case of the complex MSSM a complete calculation of the NLO EW corrections to the b anti-b annihilation channel and a consistent combination with other contributions including the standard and SUSY QCD corrections and the gg fusion, with resummation of the leading radiative corrections to the bottom-Higgs couplings and the neutral Higgs-boson propagators. We observe a large CP-violating asymmetry, arising mainly from the gg channel.
We calculate the full one-loop electroweak corrections to tri-boson production (ZZZ and WWZ) at the ILC. This is important to understand the Standard Model (SM) gauge quartic couplings which can be a window on the mechanism of spontaneous symmetry breaking. We find that even after subtracting the leading QED corrections, the electroweak corrections can still be large especially as the energy increases.
We calculate the one-loop electroweak corrections to e+e- to WWZ and e+e- to ZZZ and analyse their impacts on both the total cross section and some key distributions. These processes are important for the measurements of the quartic couplings of the massive gauge bosons which can be a window on the mechanism of spontaneous symmetry breaking. We find that even after subtracting the leading QED corrections, the electroweak corrections can still be large especially as the energy increases. We compare and implement different methods of dealing with potential instabilities in the routines pertaining to the loop integrals. For the real corrections we apply a dipole subtraction formalism and compare it to a phase-space slicing method.
We calculate the electroweak corrections to the production of WWZ and ZZZ at the linear collider in the Standard Model. These processes are important for the extraction of the quartic couplings of the massive gauge bosons which can be a window on the mechanism of spontaneous symmetry breaking. We find that the weak corrections to some kinematic distributions show new features and hence cannot be explained by an overall scale factor.
We present a new Fortran code to calculate the scalar one-loop four-point integral with complex internal masses, based on the method of 't Hooft and Veltman. The code is applicable when the external momenta fulfill a certain physical condition. In particular it holds if one of the external momenta or a sum of them is timelike or lightlike and therefore covers all physical processes at colliders. All the special cases related to massless external particles are treated separately. Some technical issues related to numerical evaluation and Landau singularities are discussed.
We calculate the leading electroweak (EW) corrections to the important process of Higgs production associated with two bottom quarks at the CERN Large Hadron Collider (LHC). Our study is restricted to the Standard Model (SM). At tree-level Higgs production in association with a b-quark pair proceeds through the small Yukawa bottom coupling in the Standard Model. Even in the limit where this coupling vanishes, EW one-loop effects, through the top-Higgs Yukawa coupling in particular, can still trigger this reaction. This contribution is small for Higgs masses around 120GeV but it quickly picks up for higher Higgs masses especially because the one-loop amplitude develops a leading Landau singularity and new thresholds open up. These effects can be viewed as the production of a pair of top quarks which rescatter to give rise to Higgs production through WW fusion. An important part of the thesis is devoted to the topic of Landau singularities in one-loop Feynman diagrams and application to the specific process of bbH production at the LHC. Since the 4-point leading Landau singularity is not integrable when the one-loop amplitude is squared, we regulate the cross section by taking into account the width of the internal top and W particles. This requires that we extend the usual box one-loop function to the case of complex masses. We show how this can be implemented analytically in our case. We study in some detail the cross section at the LHC as a function of the Higgs mass and show how some distributions can be drastically affected compared to the tree-level result.
At tree-level Higgs production in association with a b-quark pair proceeds through the small Yukawa bottom coupling in the Standard Model. Even in the limit where this coupling vanishes, electroweak one-loop effects, through the top-Higgs Yukawa coupling in particular, can still trigger this reaction. This contribution is small for Higgs masses around 120GeV but it quickly picks up for higher Higgs masses especially because the one-loop amplitude develops a leading Landau singularity and new thresholds open up. These effects can be viewed as the production of a pair of top quarks which rescatter to give rise to Higgs production through WW fusion. We study the leading Landau singularity in detail. Since this singularity is not integrable when the one-loop amplitude is squared, we regulate the cross section by taking into account the width of the internal top and W particles. This requires that we extend the usual box one-loop function to the case of imaginary masses. We show how this can be implemented analytically in our case. We study in some detail the cross section at the LHC as a function of the Higgs mass and show how some distributions can be drastically affected compared to the tree-level result.
We investigate the leading one-loop Yukawa corrections to the process pp-> b anti-b H in the Standard Model. We find that the next-to-leading order correction to the cross section is small about -4% if the Higgs mass is 120GeV. However, the appearance of leading Landau singularity when $M_H > 2M_W$ can lead to a large correction at the next-to-next-to-leading order level for a Higgs mass around 160GeV.
Considering the large value of the top Yukawa coupling, we investigate the leading one-loop Yukawa electroweak corrections that can be induced by the top quark in a process such as Higgs production in association with a tagged bottom anti-bottom pair at the LHC. At NLO these contributions are found to be small at the LHC both for the total cross section and for the distributions. In the limit of vanishing bottom Yukawa coupling where the LO contribution vanishes, the process can still be induced at one-loop through the top quark transition. Though this contribution which can be counted as part of the NNLO correction is small for Higgs masses around 120GeV, it quickly picks up for higher Higgs masses. This contribution represents the rescattering of the top quarks and their decay into W's leading to Higgs production through WW fusion
The models based on ${SU}(3)_C\otimes {SU}(3)_L \otimes {U}(1)_X$ gauge group (3-3-1) contain new Higgs bosons and one of them is the SM-like Higgs boson $h$. Production of this Higgs boson at $p p$ colliders in the framework of 3-3-1 model with right-handed neutrinos is calculated. We found that the contribution of the real $Z^\prime$ to the process $pp\to hZ$ is nearly 60 fb if $M_{Z^\prime}$ is about 1 TeV. The decay width and the branching ratios of the $Z'$ extra neutral gauge boson are systematically discussed.