Search for Higgs Pair Production in the $bb\tau\tau$ final state with the ATLAS detector at the Large Hadron Collider

This is a search for a Beyond Standard Model (BSM) heavy scalar in the ATLAS detector at 13 TeV center of mass energy using Run 2 data set recorded in 2018 with an integrated luminosity 58.5 fb$^{-1}$. The heavy scalar ($X$) decays to two Standard Model (SM) like light Higgs ($H$) bosons that decay into the $bb\tau\tau$ final state. Particularly, the semi-leptonic final state of two $\tau$'s is considered in this search where one $\tau$ decays in leptonic final state and other to a hadronic final state. No evidence of a new scalar found, so upper limits are set on the cross-section times branching ratio of the $X\rightarrow HH\rightarrow bb\tau\tau$ process with 95\% confidence interval on heavy scalar ($X$) masses between 251 and 1000 GeV.