Observation of a threshold cusp at the Λη threshold in the pK- mass spectrum with Λc+ →pK-π+ decays

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

Research output: Contribution to journalArticlepeer-review

Abstract

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 Λc+→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 Flatté function and a constant background amplitude with the reduced χ2 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.

Original languageEnglish
Article numberL031104
JournalPhysical Review D
Volume108
Issue number3
DOIs
StatePublished - 1 Aug 2023
Externally publishedYes

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