Measurement of the B -> pi/pi0/eta l n  branching ratios using semileptonic tags in the BaBar Experiment 
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Sylvie Brunet, Université de Montréal  


The branching ratio measurement of the rare semileptonic decays b->u l
n can lead to a more precise extraction of |Vub|, one of the less
known elements of the CKM matrix.  This analysis uses a new and clever
way of measuring these channels by using semileptonic tags. That
technique leads to a much cleaner sample than the traditional neutrino
reconstruction method at, however, a cost in statistics that can be
compensated by the high luminosity provided by PEPII at the Stanford
Linear Accelerator Center. At the Y(4S) used in BaBar, B mesons are
always produced in pair. The semileptonic tag technique consists in
reconstructing (tagging) one of the Bs in one of its more abundant
semileptonic b->c decays (D/D*ln) and to look for the wanted signal
(pi/pi0/eta l n) in the remaining B. This leads to an efficient
rejection of non-B backgrounds (ccbar, tau+tau-, ?) as well as most B
backgrounds since no charged track or neutral energy should remain in
the event after the tag side and the signal side selections. This
technique is particularly interesting for the pi0 l n channel since
charged B mesons are easier to tag than the neutral ones. This
presentation will give an overview of the analysis as well as the
results that can be achieved at the BaBar experiment concerning these
three semileptonic b->u l n channels.