NLO QCD + Ew Precision Study On Triple Gauge Boson Productions Including Leptonic Decays At LHC

With the discovery of the Higgs boson[1.2],all of the particles predicted by the minimal standard model(MSM)have been found.One of the main tasks of further experiments at the Large Hadron Collider(LHC)is the precise verification of the standard model(SM).One must confirm that all the theoretical predictions provided by the SM are consistent with experimental data within the margin of error.If there are any discrepancies,a possible window onto new physics opens.All of the multiple vector boson production processes at the LHC have been computed up to QCD next-to-leading order(NLO)so far.The experiments with higher energy and luminosithy will be possible in LHC Run 2.which will lead to more precision results.Only the predictions in the precision up to NLO QCD may not deliver a reliable prediction as expected.Theoretical accurate predictions are therefore ahead of us to have a thorough interpretation of data.which can be realized by taking into account the electroweak(EW)information.The triple vector boson VV’V"(V,V’,V" = W,Z or 7)production pro-cesses are relevant to the gauge couplings and gauge structure,which are used to study anomalous gauge couplings[3,4],and offer insights in understanding the electroweak symmetry spont.aneous breaking(EWSB)mechanism[5,6].In order to improve the precision of the theoretical predictions,it.is necessany to calculate at the accuracy up to QCD and EW NLO,and to include their subsequent vector boson decays.This kind of calculation thus becomes an even more important issue and was listed in the Ley Houches 2013 and 2015 Working Group wishlist[7,8].In this thesis,we present the NLO QCD + EW corrected cross sections and some kinematic distributions for the pp → WZZ + X and pp → WWW + X pro-ductions at the LHC,including the subsequent W and Z-boson leptonic decays.The obscrvables for the WZZ and WWW productions at the LHC are related to the triple couplings(WWZ,WWγ)and quartic couplings(WWZZ,WWWW).Our results show that both the NLO QCD and NLO EW corrections for these two processes are significant and should be taken into consideration in precision predictions.The NLO QCD correction from real-gluon/light-quark emission and EW correction via photon-induced channels can significantly enhance the NLO QCD correction in high energy region of final particles.We discuss the sources of uncertainty for our theoretical predictions,and provide the numerical results for scale uncertainty,PDF uncertainty and approximate NLO QCD+EW calculation uncertainty.By applying a hard jet veto in events selection,we can suppress the contribution from real jet emission and improve the convergence of the per-turbative QCD description.However,the jet veto introduces an additional scale uncertainty.These results have been published in prestigious journals and are cited by international high energy physics theorists and experimentalists[9-17].The innovations of this thesis arc listed as follows:· We present the NLO QCD + NLO EW corrected results for the pp →W±ZZ + X and pp → W±W-W+ + X productions at the LHC for the first time,which have been listed in the Les Houches wishlist for precision calculation.These are the most precise predictions for these processes by far and provide theoretical basis for the study of gauge couplings.· It’s difficult to employ direct calculations for multi-body final state pro-cesses.such as WZZ/WWW productions including leptonic decays.We adopt an improved narrow-width approximation method which reduces the complexity in calculation and preserves the spin correlation effect,and finite-width effect.· We investigate the uncertainties in theoretical predictions,including fac-torization/renormalization scale uncertainty,PDF uncertainty.αs uncer-tainty,kinematical cut induced uncertainty,and uncertainty from approx-imate NLO QCD+EW calculation.We present numerical results for scale uncertainty,PDF uncertainty and approximate NLO QCD+EW calculation uncertainty for WZZ/WWW productions.· In the calculation of one loop tensor integral,numerical instability problem will arise when the small Gram determinant occurs.We developed our dou-ble and quadruple precision codes,which can solve the instability problem as well as save CPU time.