  A method of top tagging is introduced. Using the anti-kt algorithm to define
jets, events with nj = 2 fat jets of cone size R = 1.5 are decomposed into R =
0.6 sub-jets and retained if nj (R= 0.6) >= 4 . One pair of sub-jets
reconstructs the W-mass and another jet is tagged as a b-jet, as necessary for
hadronic or semileptonic events of tt origin. This 'hollow cone' method
distinguishes the tt events from the light parton QCD dijet events.
