Subject: RE: UED simulation
From: Greg Landsberg <landsberg@hep.brown.edu>
Date: Fri, 14 Jul 2006 11:24:16 -0400
To: mercadan@fnal.gov
CC: 'Sergio Lietti' <lietti@fnal.gov>, "'Eduardo M. Gregores'" <gregores@fnal.gov>, 'Sergio Novaes' <novaes@fnal.gov>

Hi Pedro,

Thanks - this is quite revealing. It looks like the same-sign lepton branching fraction is about 2% (can you provide us with the precise number and also break it into ee, mu-mu, and e-mu categories) and we will have sensitivity up to 1/R ~ 300 GeV (100 fb) in this channel. This looks very promising, especially if we require some missing ET or presence of jets to decrease the backgrounds. The background itself should be fairly small and likely dominated by heavy flavor production with subsequent decays into muons and charge misidentification, which is small for low-pT leptons.

It would be nice to know what price we would have to pay if we require an extra (third) lepton of any sign. 5 GeV pT cut on the second-leading lepton is probably too soft for muons (and definitely too soft for electrons). I'd suggest using 10 GeV as a default (factor of ~1.7 down in cross section judging by Fig. 13) for muons and perhaps 15 GeV for electrons (what's the corresponding acceptance loss?). One thing that I find surprising is that the ratio of cross sections with 5 and 10 GeV cut seems to be constant in the entire range of 1/R between 200 and 400 GeV. This is somewhat counterintuitive, but perhaps implies that the mass splitting between the states doesn't depend much on the overall scale. However, one should have much larger jet activity for higher 1/R.

Greg