First observation of Λ+ c → ΛK+ π0 and evidence of Λ+ c → ΛK+ π + π -

• We present the first observation of the singly Cabibbo-suppressed decay Lambda thorn c ->Lambda K thorn pi 0with asignificance of5.7 sigma and the first evidence of Lambda thorn c ->Lambda K thorn pi thorn pi-decay with a significance of3.1 sigma,basedone thorn e-annihilation data recorded by the BESIII detector at the BEPCII collider. The data correspond to anintegrated luminosity of6.4fb-1, in the center-of-mass energy range from 4.600 to 4.950 GeV. Wedetermine the branching fractions of Lambda thorn c ->Lambda K thorn pi 0and Lambda thorn c ->Lambda K thorn pi thorn pi-relative to their Cabibbo-favored counterparts to beBo Lambda thorn c ->Lambda K thorn pi 0 thorn Bo Lambda thorn c ->Lambda pi thorn pi 0 thorn 1/4o2.090.39stat0.07syst thorn x10-2andBo Lambda thorn c ->Lambda K thorn pi thorn pi- thorn Bo Lambda thorn c ->Lambda pi thorn pi thorn pi- thorn 1/4o1.130.41stat0.06syst thorn x10-2, respectively. Moreover, by combining our measured result with theworld average ofBo Lambda thorn c ->Lambda pi thorn pi 0 thorn , we obtain the branching fractionBo Lambda thorn c ->Lambda K thorn pi 0 thorn 1/4o1.490.27stat0.05syst0.08ref thorn x10-3. This result significantly departs from theoretical predictionsbased on quarkSUo3 thorn flavor symmetry, which is underpinned by the presumption of meson pairS-waveamplitude dominance

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

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

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