Hi All,
concerning the determination of the (mb,a) theory related
errors (that currently seems to be the dominant uncertainty
in the Vub determination) I would like to point you to
BAD 220 (b->sg exclusive measurement).
Since the BSG BR fraction measurement has to deal with
the same input parameters for the model (mb, lambda_1)
than Vub the procedure to determine the systematic theory
error described in this note can also be applied for the Vub
measurement (see page > 189).
Here are short summary of the steps:
a) take mb (or Lambda_bar) obtained from
the bsg energy spectrum
(Important Remark: <Eg> is the only known variable which
gives direct access to mb without depending on lambda_1!!!!)
b) Input mb in the Vub model and fit for the Number of Vub events
AND the second parameter a (or lambda_1).
-> this should be straightforward since you already vary
the model parameters - now you just have to interface
it to your fit
c) vary the error on mb by +-1 Sigma and repeat the full extraction
-> this will automatically account for all correlations
between mb and lamdda_1 and the systematic error on Vub
would even be a real 68% CL (given that the input errors are 68%)
After a long discussion with Helmut(referee of BAD220), the bsg group
and myself that procedure was found to be the most "honest" and
most meaningful determination of the mb,lamda_1 theory uncertainties.
Hence it was used for ICHEP02.
Maybe thats helpful.
Oliver
