I was a bit involved in the ATLAS result. IMHO, it's not really that fancy. Basically, there's a boosted decision tree that is used to select signal-like events

I was a bit involved in the ATLAS result. IMHO, it's not really that fancy. Basically, there's a boosted decision tree that is used to select signal-like events, and it was re-optimized some new features and a larger training set. Also, they dropped a statistical categorization that was of interest for a related process in favor maximizing sensitivity to this ttH production mechanism specifically. I haven't looked too carefully at the CMS result, so no comment there.