Measurement of the branching fraction of the singly Cabibbo-suppressed decay Λ+c → ΛK+

• We report a branching fraction measurement of the singly Cabibbo-suppressed decay Λ+c → ΛK+ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of 6.44  fb−1. The branching fraction of Λ+c → ΛK+ relative to that of the Cabibbo-favored decay Λ+c → Λπ+ is measured to be R = B(Λ+c → ΛK+) / B(Λ+c → Λπ+) = (4.78±0.34±0.20)%. Combining with the world-average value of B(Λ+c → Λπ+), we obtain B(Λ+c → ΛK+) = (6.21±0.44±0.26±0.34) × 10−4. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the Λ+c→Λπ+ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that nonfactorizable contributions have been underestimated in current models.

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

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

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