The investigation of Higgs event shape and hadronic production of $ t \bar{t} (H)$

by Dr Wanli Ju (PKU)

Thursday 5 Sep 2019, 10:30 → 11:30 Asia/Shanghai

B105 (CHEP)

In this report, I would like to introduce three of my recent researches. First of all, I will present predictions for the thrust distribution in hadronic decays of the Higgs boson at the next-to-leading order and the approximate next-to-next-to-leading order. The approximate NNLO corrections are derived from a factorization formula in the soft/collinear phase-space regions, and the numeric results manifest large corrections to NLO, especially for the gluon channel. We attribute this phenomenon to the presence of non-perturbative terms like $\ln^n \tau /\tau$, and therefore perform the resummation for all these terms. Second, I will talk about a combined resummation of soft and Coulomb corrections for the associated production of the Higgs boson with a top quark pair at the LHC. In this part, the factorization formula is derived by means of pNRQCD and SCET and the similarities and critical differences between this process and the $t\bar{t}$ production process are illustrated. Making use of this factorization formula, the resummation at the improved next-to-leading logarithmic accuracy are performed, and the results are further matched onto the next-to-leading order calculation. This allows to give NLL$'$+NLO predictions for the total cross sections at the LHC. I find that the resummation effects enhance the NLO cross sections by about 6\%, and significantly reduce the scale dependence of the theoretical predictions. Third, I will calculate the invariant mass distribution of top quark pairs near the $2m_t$ threshold, where current theoretical predictions are incompatible with experimental measurements at the LHC. In order to incorporate the all order Coulomb behavior, the traditional NRQCD factorization formula is generalized for manifesting complete angular information. With this formula, the next-to-leading power resummation is performed, and from the numeric results I find that the resummation effect significantly enhances the differential cross section in the threshold region, and makes the theoretical prediction more compatible with experimental data.