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