Search of New Physics with Boosted Higgs Boson in Hadronic Final States with ATLAS Detector

The discovery of a Higgs boson at the Large Hadron Collider (LHC) confirms the validity of the Standard Model (SM) in the description of particle interactions at electroweak scale. However, radioactive corrections to the Higgs mass drives its value to the model's validity limit, indicating either extreme fine-tuning or the presence of new physics at higher energy scale. Since 2015, the LHC starts its Run 2 journey with unprecedented center of mass energy of 13 TeV. Along with increase in luminosity, this greatly extends the sensitivity of ATLAS experiment to heavy new particles at TeV scale. In particular, many new physics models beyond the Standard Model manifest themselves through significant coupling to the Higgs boson in decays of new particles to a Higgs boson and other SM particles. In this work, two searches for resonances decaying to either pair of Higgs bosons or a Higgs boson associated with another SM vector boson in all hadronic final states are presented using data collected by ATLAS during Run 2. Due to the heavy mass of new resonance, Higgs boson and W/Z boson can be boosted to large momentum, causing their decay products to be collimated. The dominant $H\rightarrow b\bar{b}$ decay mode also provides a clear signature through displaced vertices. A powerful boosted boson identification technique fully exploiting such jet substructure and heavy flavor information is therefore developed and used in both searches to suppress the dominant multijet backgrounds and largely enhance search sensitivity in particular for very high resonance mass. In the absence of significant excess, new exclusion limits are set on benchmark new physics models.