Theoretical Physics Group

The invariant mass spectrum of the lepton pair in inclusive semileptonic B → Xulν decay yields a model independent determination of |Vub| [1]. Unlike the lepton energy and hadronic invariant mass spectra, nonperturbative effects are only important in the resonance region, and play a parametrically suppressed role when dΓ/dq is integrated over q > (mB − mD) , which is required to eliminate the B → Xclν background. We discuss these backgrounds for q slightly below (mB −mD) , and point out that instead of q > (mB − mD) 2 = 11.6GeV, the cut can be lowered to q > ∼ 10.5GeV . This is important experimentally, particularly when effects of a finite neutrino reconstruction resolution are included.