Measurement of the lepton forward-backward asymmetry in $B \rightarrow X_s \ell^+ \ell^-$ decays with a sum of exclusive modes

We report the first measurement of the lepton forward-backward asymmetry AFB as a function of the squared four-momentum of the dilepton system, q2, for the electroweak penguin process B→Xsℓ+ℓ- with a sum of exclusive final states, where ℓ is an electron or a muon and Xs is a hadronic recoil system with an s quark. The results are based on a data sample containing 772×106 BB¯ pairs recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e+e- collider. AFB for the inclusive B→Xsℓ+ℓ- is extrapolated from the sum of 10 exclusive Xs states whose invariant mass is less than 2 GeV/c2. For q2>10.2 GeV2/c2, AFB<0 is excluded at the 2.3σ level, where σ is the standard deviation. For q2<4.3 GeV2/c2, the result is within 1.8σ of the standard model theoretical expectation.

Note:

13 pages, 23 figures, Belle Preprint 2014-1, KEK preprint 2013-60

angular distribution: asymmetry
electroweak interaction: penguin
recoil: hadronic
lepton: angular distribution
BELLE
KEK-B
electron positron: annihilation
B: pair production
B: semileptonic decay
dilepton: final state

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Measurement of the lepton forward-backward asymmetry in B→Xsℓ+ℓ−B \rightarrow X_s \ell^+ \ell^-B→Xs​ℓ+ℓ− decays with a sum of exclusive modes

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Measurement of the lepton forward-backward asymmetry in $B \rightarrow X_s \ell^+ \ell^-$ decays with a sum of exclusive modes