Measurement of the lepton forward-backward asymmetry in B -˃ X(s)l(+)l(-) decays with a sum of exclusive modes

Abstract

We report the first measurement of the lepton forward-backward asymmetry A(FB) as a function of the squared four-momentum of the dilepton system, q(2), for the electroweak penguin process B -˃ X(s)l(+)l(-) with a sum of exclusive final states, where l is an electron or a muon and X-s is a hadronic recoil system with an s quark. The results are based on a data sample containing 772 x 10(6) B (B) over bar pairs recorded at the gamma (4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. A(FB) for the inclusive B -˃ X(s)l(+)l(-) is extrapolated from the sum of 10 exclusive X-s states whose invariant mass is less than 2 GeV/c(2). For q(2) ˃ 10.2 GeV2/c(2), A(FB) ˂ 0 is excluded at the 2.3 sigma level, where sigma is the standard deviation. For q(2) ˂ 4.3 GeV2/c(2), the result is within 1.8 sigma of the standard model theoretical expectation.