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Observation of a threshold cusp at the $Λ η$ threshold in the $p K^{-}$ mass spectrum with $Λ_{c}^{+} \to p K^{-} π^{+}$ decays

S. B. Yang , K. Tanida , J. K. Ahn , I. Adachi , H. Aihara , D. M. Asner , H. Atmacan , V. Aulchenko , T. Aushev et al. (Belle Collaboration)

T. Aushev , R. Ayad , V. Babu , P. Behera , K. Belous , J. Bennett , M. Bessner , V. Bhardwaj , B. Bhuyan , D. Bodrov , J. Borah , A. Bozek , M. 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 , and V. Zhukova (Belle Collaboration)

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Phys. Rev. D 108, L031104 – Published 16 August, 2023

DOI: https://doi.org/10.1103/PhysRevD.108.L031104

Abstract

We observe a narrow peaking structure in the $p K^{-}$ invariant-mass spectrum near the $Λ η$ threshold. The peak is clearly seen in 1.5 million events of $Λ_{c}^{+} \to p K^{-} π^{+}$ 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 $Λ η$ threshold. The best fit is obtained with a coherent sum of a Flatté function and a constant background amplitude with the reduced $χ^{2}$ of $257 / 243$ ( $p = 0.25$ ), while the fits to Breit-Wigner functions are unfavored by more than $7 σ$ . The best fit explains the structure as a cusp at the $Λ η$ 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.

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References (28)

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Phys. Rev. D 108, L031104– Published 16 August, 2023

Vol. 108, Iss. 3 — 1 August 2023

Received 1 September 2022
Revised 6 January 2023
Accepted 9 July 2023

DOI: https://doi.org/10.1103/PhysRevD.108.L031104

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Observation of a threshold cusp at the $Λ η$ threshold in the $p K^{-}$ mass spectrum with $Λ_{c}^{+} \to p K^{-} π^{+}$ decays

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

Abstract

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (28)

Observation of a threshold cusp at the $Λ η$ threshold in the $p K^{-}$ mass spectrum with $Λ_{c}^{+} \to p K^{-} π^{+}$ decays