• ytest250_wjet.eps: Test of y distributions include SUSY and W+Jet SM events

Things to note: There is a 250 GeV cut applied to all jets here, but nevertheless the transverse momentum distributions will be different. What I expected was:

• Scale for W splitting depends on the W mass so doesn't care what process the W comes from, or what the PT of the W is. This seems to be largely true, from the top plot.
• Scale for QCD jet splitting depends on the PT of the jet, and so can be rather different for QCD jets in SUSY events (which I think are generally higher PT). So I understand the top plot.
• y cut I would expect to be the same for QCD jets wherever they come from (modulo logarithmic corrections for running alpha_s). The differences between QCD jets in SUSY and W+jet look quite large to me, but maybe this is consistent with scaling. I might look into this further, maybe by reweighting the PT distributions and seeing if the y is then equal.
• I would have expected the y cut for the W's to be more different than it is. Perhaps it is so similar because both distributions are peaked around the cutoff at 250 GeV.

Some ideas to try on refining the selection...

• run the kt algorithm with R parameter < 1 (0.7 and 0.5 are two common values)? This may improve the W mass resolution but at some point the W's will stop being in a single jet and the method breaks.