Observation of a threshold cusp at the Λη threshold in the pK^- mass spectrum with Λ$$^{+}_{c}$$ → pK^-π⁺ decays

Journal Article · 16 August 2023 · Physical Review. D.

DOI: https://doi.org/10.1103/physrevd.108.l031104 · OSTI ID:2424177

Yang, S.  B. ; Tanida, K. ; Ahn, J.  K. ; Adachi, I. ; Aihara, H. ; Asner, D.  M. ; Atmacan, H. ; Aulchenko, V. ; Aushev, T. ; Ayad, R. ; Babu, V. ; Behera, P. ; Belous, K. ; Bennett, J. ; Bessner, M. ; Bhardwaj, V. ; Bhuyan, B. ; Bodrov, D. ; Borah, J. ; Bozek, A. ; Bračko, M. ; Branchini, P. ; Browder, T.  E. ; Budano, A. ; Campajola, M. ; Červenkov, D. ; Chang, M. -C. ; Chang, P. ; 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 Pietro, G. ; Dhamija, R. ; Di Capua, F. ; Doležal, Z. ; Dong, T.  V. ; Dossett, D. ; Epifanov, D. ; Fulsom, B.  G. ; Garg, R. ; Gaur, V. ; Garmash, A. ; Giri, A. ; Goldenzweig, P. ; Graziani, E. ; Gu, T. ; Guan, Y. ; Gudkova, K. ; Hadjivasiliou, C. ; Hayasaka, K. ; Hayashii, H. ; Hou, W. -S. ; Hsu, C. -L. ; Iijima, T. ; Inami, K. ; Ipsita, N. ; Ishikawa, A. ; Itoh, R. ; Iwasaki, M. ; Iwasaki, Y. ; Jacobs, W.  W. ; Jang, E. -J. ; Ji, Q.  P. ; Jia, S. ; Jin, Y. ; Joo, K.  K. ; Kang, K.  H. ; Karyan, G. ; Kawasaki, T. ; Kichimi, H. ; Kiesling, C. ; Kim, C.  H. ; Kim, D.  Y. ; Kim, K. -H. ; Kim, Y.  J. ; Kim, Y. -K. ; Kindo, H. ; Kodyš, P. ; Konno, T. ; Korobov, A. ; Korpar, S. ; Kovalenko, E. ; Križan, P. ; Krokovny, P. ; Kumar, M. ; Kumar, R. ; Kumara, K. ; Kwon, Y. -J. ; Lam, T. ; Lange, J.  S. ; Laurenza, M. ; Lee, J.  Y. ; Lee, S.  C. ; Li, C.  H. ; Li, J. ; Li, L.  K. ; Li, Y. ; Li Gioi, L. ; Libby, J. ; Lieret, K. ; Liventsev, D. ; Luo, T. ; Masuda, M. ; Matsuda, T. ; Matvienko, D. ; Maurya, S.  K. ; Meier, F. ; Merola, M. ; Metzner, F. ; Miyabayashi, K. ; Mizuk, R. ; Mohanty, G.  B. ; Nakamura, I. ; Nakano, T. ; Nakao, M. ; Natkaniec, Z. ; Natochii, A. ; Nayak, L. ; Niiyama, M. ; Nisar, N.  K. ; Nishida, S. ; Ono, H. ; Oskin, P. ; Pakhlov, P. ; Pakhlova, G. ; Pardi, S. ; Park, H. ; Park, S. -H. ; Passeri, A. ; Patra, S. ; Paul, S. ; Pedlar, T.  K. ; Pestotnik, R. ; Piilonen, L.  E. ; Podobnik, T. ; Prencipe, E. ; Prim, M.  T. ; Rout, N. ; Russo, G. ; Sandilya, S. ; Santelj, L. ; Savinov, V. ; Schnell, G. ; Schueler, J. ; Schwanda, C. ; Seino, Y. ; Senyo, K. ; Sevior, M.  E. ; Shapkin, M. ; Sharma, C. ; Shen, C.  P. ; Shiu, J. -G. ; Singh, J.  B. ; Sokolov, A. ; Solovieva, E. ; Starič, M. ; Sumihama, M. ; Sumiyoshi, T. ; Sutcliffe, W. ; Takizawa, M. ; Tamponi, U. ; Tenchini, F. ; Trabelsi, K. ; Tsuboyama, T. ; Uchida, M. ; Uglov, T. ; Unno, Y. ; Uno, S. ; Ushiroda, Y. ; Usov, Y. ; van Tonder, R. ; Varner, G. ; Vossen, A. ; Waheed, E. ; Wang, E. ; Wang, M. -Z. ; Wang, X.  L. ; Watanabe, M. ; Watanuki, S. ; Werbycka, O. ; Won, E. ; Yabsley, B.  D. ; Yan, W. ; Yelton, J. ; Yin, J.  H. ; Yuan, C.  Z. ; Yusa, Y. ; Zhai, Y. ; Zhang, Z.  P. ; Zhilich, V. ; Zhukova, V.

We observe a narrow peaking structure in the pK^- invariant-mass spectrum near the Λη threshold. The peak is clearly seen in 1.5 million events of Λ$$^{+}_{c}$$ → pK^-π⁺ decay using the 980 fb^-1 data sample collected by the Belle detector at the KEKB asymmetric-energy e⁺e^-collider. We try two approaches to explain this structure: as a new resonance and as a cusp at the Λη threshold. The best fit is obtained with a coherent sum of a Flatte function and a constant background amplitude with the reduced X² of 257/243 (p = 0.25), while the fits to Breit-Wigner functions are unfavored by more than 7σ. The best fit explains the structure as a cusp at the Λη threshold, and the obtained parameters are consistent with the known properties of Λ(1670). The observation gives the first identification of a threshold cusp in hadrons from the spectrum shape.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• Contributing Organization: Belle Collaboration
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 2424177
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 3 Vol. 108; ISSN 2470-0010
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English