$\it{b}$-tagging in dense environments

This note describes the performance of the common ATLAS b-tagging algorithms in thecontext of the dense environments that can be found in the decay of boosted top quarks intojets and addresses the problems related to such conditions. The results of these studies leadto the development of a new multivariate-analysis-based b-tagging algorithm called MVb.The training of this new b-tagging algorithm is modified with respect to that of the currenttools to take the conditions of boosted topologies better into account. Its performance is significantlyimproved relative to the standard algorithms for high pT b-jets and jets containedin dense environment