Improved jet substructure methods: Y-splitter and variants with grooming

It has recently been demonstrated with Monte Carlo studies that combining the
well-known Y-splitter and trimming techniques gives rise to important gains in the signal signicance achievable for boosted electroweak boson tagging at high pt. Here we carry out analytical calculations that explain these ndings from rst principles of QCD both for grooming via trimming and via the modied mass-drop tagger (mMDT). We also suggest modications to Y-splitter itself, which result in great simplications to the analytical results both for pure Y-splitter as well as its combination with general grooming methods. The modications also lead to further performance gains, while making the results largely independent of choice of groomer. We discuss the implications of these findings in the broader context of optimal methods for boosted object studies at hadron colliders.