B -> eta() l nu decays and the flavor-singlet form factor
Abstract
We study semileptonic decays B -> eta() l nu, taking into account the flavor-singlet contribution (Fsinglet+) to the B -> eta() form factors, which arises from the two-gluon emission in a decaying B meson. It has been recently pointed out that, in addition to large weak annihilation effects, the unknown value of Fsinglet+ prevents accurate theoretical estimates in the analysis of B -> eta K decays in QCD factorization. We present a certain method to determine Fsinglet+ with a reasonable accuracy, using B -> eta() l nu and B -> pi l nu decays. We also investigate the possible effect of Fsinglet+ on the estimated branching ratios (BRs) for B -> eta() l nu and find that the BR for B -> eta l nu is particularly sensitive to the effect of Fsinglet+.
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