Hi, I tried to compute the systematics from the mes fit. First let me remind you how the fit is performed. After all cuts a fit to the mes distribution for Mx<2.5 is performed with all parameter floating in order to get the signal parameters. Then those parameters are fixed in all the mes fit in each Mx bin. I repeated the fit varing those signal parameters within their error. This is the change in the fitted BRBR value: * +1 sigma in mean gauss (cry ball) +0.0 * 10^-3 (+0%) * -1 sigma in mean gauss (cry ball) +0.01 * 10^-3 (+0.6%) * +1 sigma in sigma gauss (cry ball) +0.20 * 10^-3 (+1.2%) * -1 sigma in sigma gauss (cry ball) -0. * 10^-3 * +1 sigma in alpha param (cry. ball) -0.50 * 10^-3 (-3%) * -1 sigma in alpha param (cry. ball) +0.48 * 10^-3 (+2.8%) * +1 sigma in n param (cry. ball) -0.30 * 10^-3 (-1.8%) * -1 sigma in n param (cry. ball) +0.88 * 10^-3 (+5.2%) -------------------------------------------------------------------- total +1.02 +6% -0.58 -3.5% As a crosscheck I ran the fit leaving floating the cb parameters (alpha and n) in each Mx bin fit. I got BRBR = 0.0178748 +- 0.00488316(stat) +- 0.00146808(MC stat) that is +5.8%, then is within the systematics. This numbers, together with the crystall ball vs gaussian fit difference(1.2%), will give the systematics from the mes fit. +6.1% -3.7% We are also forgetting the error from the fit for Nsl. It has a stat error of 1.6%. Daniele