Search for right-handed W gauge boson decaying into charged lepton and boosted right-handed neutrino in 139 fb-1 of sqrt(s) = 13 TeV proton-proton collisions with the ATLAS detector

The standard model (SM) gives a successful description for almost the all phenomena of particle physics. However, there are some problems such as the observation of tiny masses of left-handed neutrinos and baryon dominance in the universe. One possible model which solve these inconsistencies is the left-right symmetric model (LRSM) accompanying right-handed neutrinos N_R and right-handed W boson W_R. A search for W_R decaying into N_R, pp -> W_R+- -> l+- N_R -> l+- l+- q q', in the framework of LRSM is presented in this thesis. The analysis is based on a proton-proton collisions data at a center-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider in 2015 - 2018, corresponding to an integrated luminosity of 139 fb-1. The search is performed in both electron and muon final states, using a large-radius jet to reconstruct the decay products from the N_R -> l q q', targeting on the phase space with large mass splitting between W_R and N_R, dM = m(W_R) - m(N_R). Depending on the dM, two analysis strategies are considered in the electron channel; one is to identify the electron from the N_R decay as isolated from the large-radius jet; the other is to reconstruct the N_R -> e q q' as a single large-radius jet. In the muon channel, two muons are always required, since the higher efficiency can be kept even for large dM signals. Event selection, strategies of the dominant background estimations are developed. No excess is observed in all lepton flavour final states and W_R mass is excluded up to 6.4 TeV for the N_R mass of 1.0 TeV at 95% confidence level. Compared to the previous LHC analyses, it corresponds to the expansion of exclusion limits by 1.5 TeV and 1.4 TeV for electron and muon final states, respectively.