First Observation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Λ</mml:mi><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Λ</mml:mi><mml:msup><mml:mi>π</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math> Signals near the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true"><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mrow></mml:mover><mml:mi>N</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>I</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> Mass Threshold in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">Λ</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup><mml:mo stretchy="false">→</mml:mo><mml:mi mathvariant="normal">Λ</mml:mi><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> Decay
Yue Ma, J. Yelton, K. Tanida, I. Adachi, J. K. Ahn, H. Aihara, S. Al Said, D. M. Asner, H. Atmacan, T. Aushev, R. Ayad, V. Babu, S. Bahinipati, Sw. Banerjee, P. K. Behera, K. Belous, J. V. Bennett, M. Bessner, B. Bhuyan, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, J. Borah, A. Bożek, M. Bračko, P. Branchini, T. E. Browder, A. Budano, M. Campajola, D. Červenkov, M.-C. Chang, A. Chen, B. G. Cheon, K. Chilikin, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, Y. Choi, S. Choudhury, D. Cinabro, S. Das, G. De Nardo, G. De Pietro, R. Dhamija, F. Di Capua, J. Dingfelder, Z. Doležal, T. V. Dong, D. Epifanov, T. Ferber, D. Ferlewicz, B. G. Fulsom, R. Garg, V. Gaur, A. Garmash, A. Giri, P. Goldenzweig, B. Golob, E. Graziani, K. Gudkova, C. Hadjivasiliou, S. Halder, K. Hayasaka, H. Hayashii, M. T. Hedges, W.-S. Hou, C.-L. Hsu, K. Inami, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, W. W. Jacobs, E.-J. Jang, S. Jia, Y. Jin, A. B. Kaliyar, K. H. Kang, T. Kawasaki, C. Kiesling, C. H. Kim, D. Y. Kim, Y.-K. Kim, K. Kinoshita, P. Kodyš, A. Korobov, S. Korpar, E. Kovalenko, P. Križan, P. Krokovny, R. Kumar, K. Kumara, Y.-J. Kwon, T. Lam, J. S. Lange, S. C. Lee, P. Lewis, L. K. Li
Abstract
Using the data sample of $980\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected with the Belle detector operating at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider, we present the results of an investigation of the $\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+}$ and $\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{\ensuremath{-}}$ invariant mass distributions looking for substructure in the decay ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$. We find a significant signal in each mass distribution. When interpreted as resonances, we find for the $\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{+}$ ($\mathrm{\ensuremath{\Lambda}}{\ensuremath{\pi}}^{\ensuremath{-}}$) combination a mass of $1434.3\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.9(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ [$1438.5\ifmmode\pm\else\textpm\fi{}0.9(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}2.5(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$], an intrinsic width of $11.5\ifmmode\pm\else\textpm\fi{}2.8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}5.3(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ [$33.0\ifmmode\pm\else\textpm\fi{}7.5(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}23.6(\mathrm{syst})\text{ }\text{ }\mathrm{MeV}/{c}^{2}$] with a significance of $7.5\ensuremath{\sigma}$ ($6.2\ensuremath{\sigma}$). As these two signals are very close to the $\overline{K}N$ threshold, we also investigate the possibility of a $\overline{K}N$ cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.