Direct Measurement of the Branching Fractions B (ψ (3686) →j /ψX) and B (ψ (3770) →j /ψX), and Observation of the State R (3760) in e+e- →j /ψ X

(BESIII Collaboration)

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We report a measurement of the observed cross sections of e+e-→J/ψX based on 3.21 fb-1 of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. In analysis of the cross sections, we measured the decay branching fractions of B(ψ(3686)→J/ψX)=(64.4±0.6±1.6)% and B(ψ(3770)→J/ψX)=(0.5±0.2±0.1)% for the first time. The energy-dependent line shape of these cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays ψ(3686)→J/ψX and ψ(3770)→J/ψX. Instead, it can be better described with one more BW amplitude of the decay R(3760)→J/ψX. Under this assumption, we extracted the R(3760) mass MR(3760)=3766.2±3.8±0.4 MeV/c2, total width ΓR(3760)tot=22.2±5.9±1.4 MeV, and product of leptonic width and decay branching fraction ΓR(3760)eeB[R(3760)→J/ψX]=(79.4±85.5±11.7) eV. The significance of the R(3760) is 5.3σ. The first uncertainties of these measured quantities are from fits to the cross sections and second systematic.

Original languageEnglish (US)
Article number082002
JournalPhysical review letters
Issue number8
StatePublished - Aug 20 2021
Externally publishedYes

Bibliographical note

Funding Information:
The BESIII Collaboration thank the staff of BEPCII and the IHEP computing center for their strong support. This work is supported in part by National Key Basic Research Program of China under Contracts No. 2009CB825204 and No. 2015CB856700; National Key R&D Program of China under Contract No. 2020YFA0406400; National Natural Science Foundation of China (NSFC) under Contracts No. 10935007, No. 11625523, No. 11635010, No. 11735014, No. 11822506, No. 11835012, and No. 11961141012; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. U1532257, No. U1532258, No. U1732263, and No. U1832207; CAS Key Research Program of Frontier Sciences under Contracts No. QYZDJ-SSW-SLH003 and No. QYZDJ-SSW-SLH040; 100 Talents Program of CAS; CAS Other Research Program under Code No. Y129360; INPAC and Shanghai Key Laboratory for Particle Physics and Cosmology; ERC under Contract No. 758462; German Research Foundation DFG under Contracts No. Collaborative Research Center CRC 1044 and No. FOR 2359; Istituto Nazionale di Fisica Nucleare, Italy; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Science and Technology fund; STFC (United Kingdom); The Knut and Alice Wallenberg Foundation (Sweden) under Contract No. 2016.0157; The Royal Society, United Kingdom under Contracts No. DH140054 and No. DH160214; The Swedish Research Council; and U.S. Department of Energy under Contracts No. DE-FG02-05ER41374, No. DE-SC-0010118, and No. DE-SC-0012069.

Publisher Copyright:
© 2021 authors. Published by the American Physical Society.


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