Measurement of the Higgs boson mass in the $H \rightarrow ZZ* \rightarrow 4\ell$ decay channel with $\sqrt{s} = 13$ TeV $pp$ collisions using the ATLAS detector at the LHC

The mass of the Higgs boson is an important parameter in the Standard Model as it affects the predictions of observables related to the Higgs boson. Higher precision measurements of its mass are therefore of fundamental importance. The $H \rightarrow ZZ* \rightarrow 4\ell$ channel ($\ell = e,\mu$) provides a fully reconstructable final state with good resolution and a high signal-to-background ratio. Using the proton-proton collision data delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015-2018, we present the most recent measurement of the Higgs Boson mass in this final state. Using this 139 fb$^{-1}$ dataset, we are able to reduce the uncertainty in the mass measurement by almost a factor of 2.