Higgs rare decays at ATLAS and CMS

More than a decade has passed since the start of the operation of the Large Hadron Collider at CERN and the discovery of the Higgs boson by the ATLAS and CMS Collaborations. The so far observed Higgs boson decay modes cover around 90$\%$ of the total Higgs boson width. The rare and yet unobserved Higgs boson decay channels could potentially be affected by the new physics, beyond the Standard Model. It is then crucial to search for these experimentally challenging decay modes in order to have a more complete characterisation of the Higgs boson physics sector. This was enabled with LHC Run 2 data having both increase in the Higgs production rate, with increased energy, and also the increase in the recorded luminosity. Both ATLAS and CMS have refined and advanced their analysis techniques, contributing further to increase in Higgs analyses sensitivity.