First observation of the semileptonic decay Λ+c → pK−e+νe

• Using 4.5  fb−1 of e+e− annihilation data samples collected at the center-of-mass energies ranging from 4.600 GeV to 4.699 GeV with the BESIII detector at the BEPCII collider, a first study of the semileptonic decays Λ+c→pK−e+νe, Λ+c→Λ(1520)e+νe and Λ+c→Λ(1405)e+νe is performed. The Λ+c→pK−e+νe decay is observed with a significance of 8.2σ and the branching fraction is measured to be B(Λ+c→pK−e+νe)=(0.88±0.17stat±0.07syst)×10−3. We also report evidence of Λ+c→Λ(1520)e+νe and Λ+c→Λ(1405)e+νe with significances of 3.3σ and 3.2σ, respectively, and measure B(Λ+c→Λ(1520)e+νe)=(1.02±0.52stat±0.11syst)×10−3 and B(Λ+c→Λ(1405)[→pK−]e+νe)=(0.42±0.19stat±0.04syst)×10−3. Combining these with the inclusive semileptonic Λ+c branching fraction measured by BESIII, the relative fraction is determined to be [B(Λ+c→pK−e+νe)/B(Λ+c→Xe+νe)]=(2.1±0.4stat±0.2syst)%, which provides a clear confirmation that semileptonic Λ+c decays are not saturated by the Λℓ+νℓ final state.

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NATURVETENSKAP  -- Fysik -- Subatomär fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Subatomic Physics (hsv//eng)

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