Hi, we also computed a correction factor for the signal/peaking bkg using the entire mx distribution, not a bin by bin. In this case the fit looks better, with respect to the bin by bin one: http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fix129/test_fix129fitresults.eps http://www.slac.stanford.edu/~petrella/tmp/scra/Ibutest_fixed/test_fixedfitresults.eps cheers, Antonio