Measurement of the branching fraction of the singly Cabibbo-suppressed decay <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>c</mml:mi><mml:mo>+</mml:mo></mml:msubsup><mml:mo stretchy="false">→</mml:mo><mml:mi mathvariant="normal">Λ</mml:mi><mml:msup><mml:mi>K</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math>
M. Ablikim, М. Н. Ачасов, P. Adlarson, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, X. H. Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, Shida Bao, V. Batozskaya, D. Becker, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai, X. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Çetin, J. F. Chang, W. L. Chang, G. Chelkov, C. Chen, Chao Chen, G. Chen, H. S. Chen, M. L. Chen, S. J. Chen, S. M. Chen, T. Chen, X. R. Chen, X. T. Chen, Y. B. Chen, Z. J. Chen, W. S. Cheng, S. K. Choi, X. Chu, G. Cibinetto, F. Cossio, J. J. Cui, H. L. Dai, J. P. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, Wenxing Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, K. Fischer, M. Fritsch, C. Fritzsch, C. D. Fu, He Gao, Yang Gao, Yang Gao, S. Garbolino, I. Garzia, P. Ge, Z. W. Ge, C. Geng, E. Gersabeck, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl
Abstract
We report a branching fraction measurement of the singly Cabibbo-suppressed decay ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+}$ 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 $6.44\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The branching fraction of ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+}$ relative to that of the Cabibbo-favored decay ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+}$ is measured to be $\mathcal{R}=\frac{\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+})}{\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+})}=(4.78\ifmmode\pm\else\textpm\fi{}0.34\ifmmode\pm\else\textpm\fi{}0.20)%$. Combining with the world-average value of $\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+})$, we obtain $\mathcal{B}({\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{K}^{+})=(6.21\ifmmode\pm\else\textpm\fi{}0.44\ifmmode\pm\else\textpm\fi{}0.26\ifmmode\pm\else\textpm\fi{}0.34)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+}$ 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.