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Hello, I have a question. In VubRecoil studies, like the one in BAD 540, one of the things they do is measure the spectra of variables like mX and pl. So in order to remove the breco background, they have to sort the events into bins of mX or pl, and perform a separate mes fit in each bin. Specifically, for the mX fit, the Crystal Ball parameters are determined from a fit to the full sample, and fixed in the bin-by-bin fits. The Argus parameters are floated in the bin-by-bin fits. * for background, mes varies so much with mX or pl that is is worth the loss of statistics (from the binning) to determine the breco background bin-by-bin. * for signal, mes does not vary enough with mX or pl to make it worthwhile to bin the data and incur the loss of statistics. OR * for signal, we do not have enough faith in the Crystal Ball function to trust it in a bin-by-bin fit. OR BOTH. So my questions are: * Is my interpretation correct? * If so, then WHY would mes background vary so much with mX or pl? I can see how mes might vary with the QUALITY of mX, since a badly-reco'd reco-B meson would lead to a badly-reco'd X. But ultimately the two B mesons decay independently, so I don't see why mes should affect the mX or pl distributions very much. And yet they must, or there would be no need for a bin-by-bin fit. I hope that's not a stupid question. I'm still kind of new to this stuff. Thanks for your help, sheila