First Observation of Λπ+ and Λπ- Signals near the KN(I=1) Mass Threshold in Λc+→Λπ+π+π- Decay

Ma, Y; Yelton, J; Tanida, K; Adachi, I; Ahn, J K; Aihara, H; Al Said, S; Asner, D M; Atmacan, H; Aushev, T; Ayad, R; Babu, V; Bahinipati, S; Banerjee, Sw; Behera, P; Belous, K; Bennett, J; Bessner, M; Bhuyan, B; Bilka, T; Biswas, D; Bobrov, A; Bodrov, D; Borah, J; Bozek, A; Bračko, M; Branchini, P; Browder, T E; Budano, A; Campajola, M; Červenkov, D; Chang, M-C; Chen, A; Cheon, B G; Chilikin, K; Cho, H E; Cho, K; Cho, S-J; Choi, S-K; Choi, Y; Choudhury, S; Cinabro, D; Das, S; De Nardo, G; De Pietro, G; Dhamija, R; Di Capua, F; Dingfelder, J; Doležal, Z; Dong, T V; Epifanov, D; Ferber, T; Ferlewicz, D; Fulsom, B G; Garg, R; Gaur, V; Garmash, A; Giri, A; Goldenzweig, P; Golob, B; Graziani, E; Gudkova, K; Hadjivasiliou, C; Halder, S; Hayasaka, K; Hayashii, H; Hedges, M T; Hou, W-S; Hsu, C-L; Inami, K; Ipsita, N; Ishikawa, A; Itoh, R; Iwasaki, M; Jacobs, W W; Jang, E-J; Jia, S; Jin, Y; Kaliyar, A B; Kang, K H; Kawasaki, T; Kiesling, C; Kim, C H; Kim, D Y; Kim, Y-K; Kinoshita, K; Kodyš, P; Korobov, A; Korpar, S; Kovalenko, E; Križan, P; Krokovny, P; Kumar, R; Kumara, K; Kwon, Y-J; Lam, T; Lange, J S; Lee, S C; Lewis, P; L K, Li; Li, Y; Li Gioi, L; Libby, J; Lieret, K; Lin, Y-R; Liventsev, D; Luo, T; Masuda, M; Matsuda, T; Matvienko, D; Maurya, S K; Meier, F; Merola, M; Metzner, F; Miyabayashi, K; Mohanty, G B; Mussa, R; Nakamura, I; Nakano, T; Nakao, M; Natkaniec, Z; Natochii, A; Nayak, L; Nayak, M; Nisar, N K; Nishida, S; Ogawa, S; Ono, H; Oskin, P; Pakhlov, P; Pakhlova, G; Pardi, S; Park, H; Park, J; Patra, S; Paul, S; Pestotnik, R; Piilonen, L E; Podobnik, T; Prencipe, E; Prim, M T; Rostomyan, A; Rout, N; Russo, G; Sandilya, S; Santelj, L; Savinov, V; Schnell, G; Schueler, J; Schwanda, C; Seino, Y; Senyo, K; Sevior, M E; Shan, W; Shapkin, M; Sharma, C; Shen, C P; Shiu, J-G; Simon, F; Sokolov, A; Solovieva, E; Starič, M; Sumihama, M; Sumiyoshi, T; Sutcliffe, W; Takizawa, M; Tamponi, U; Tenchini, F; Uchida, M; Uehara, S; Uglov, T; Unno, Y; Uno, K; Uno, S; Urquijo, P; Usov, Y; Vahsen, S E; van Tonder, R; Varner, G; Vinokurova, A; Vossen, A; Wang, D; Wang, M-Z; Watanabe, M; Watanuki, S; Werbycka, O; Won, E; Xu, X; Yabsley, B D; Yan, W; Yang, S B; Yin, J H; Yuan, C Z; Yuan, L; Zhang, Z P; Zhilich, V; Zhukova, V

doi:10.1103/PhysRevLett.130.151903

Using the data sample of 980 fb-1 collected with the Belle detector operating at the KEKB asymmetric-energy e+e- collider, we present the results of an investigation of the Λπ+ and Λπ- invariant mass distributions looking for substructure in the decay Λc+→Λπ+π+π-. We find a significant signal in each mass distribution. When interpreted as resonances, we find for the Λπ+ [Λπ-] combination a mass of 1434.3±0.6(stat)±0.9(syst) MeV/c2 [1438.5±0.9(stat)±2.5(syst) MeV/c^2], an intrinsic width of 11.5±2.8(stat)±5.3(syst) MeV/c2 [33.0±7.5(stat)±23.6(syst) MeV/c2] with a significance of 7.5σ (6.2σ). As these two signals are very close to the KN threshold, we also investigate the possibility of a KN cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.