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  1. First measurements of the absolute branching fraction of Λ c ( 2625 ) + Λ c + π + π and upper limit on Λ c ( 2595 ) + Λ c + π + π

    Tmore » he absolute branching fraction of the decay Λ c ( 2625 ) + Λ c + π + π is measured for the first time to be ( 50.2 ± 5.7 stat ± 3.5 syst ) % with 368.48 pb 1 of e + e collision data collected by the BESIII detector at the center-of-mass energies of s = 4.918 and 4.950 GeV. Although the central value of the result is lower than the theoretical prediction of 67%, obtained from isospin symmetry, they are consistent taking the uncertainties into account. his is the first absolute branching fraction measurement for Λ c ( 2625 ) + since it was found. his measurement is necessary to obtain the coupling constants for the transitions between s -wave and p -wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λ c ( 2595 ) + Λ c + π + π . No significant signal is observed, and the upper limit on its branching fraction is determined to be 85.0% at the 90% confidence level. Published by the American Physical Society 2024« less
  2. Cross section measurement of e + e η ψ ( 2 S ) and search for e + e η X ˜ ( 3872 )

    Tmore » he energy-dependent cross section for e + e η ψ ( 2 S ) is measured at 18 center of mass energies from 4.288 to 4.951 GeV using the BESIII detector. Using the same data samples, we also perform the first search for the reaction e + e η X ˜ ( 3872 ) , but no evidence is found for the X ˜ ( 3872 ) in the π + π J / ψ mass distribution. At each of the 18 center of mass energies, upper limits at the 90% confidence level on the cross section for e + e η ψ ( 2 S ) and on the product of the e + e η X ˜ ( 3872 ) cross section with the branching fraction of X ˜ ( 3872 ) π + π J / ψ are reported. Published by the American Physical Society 2024« less
  3. First Study of Antihyperon-Nucleon Scattering Λ ¯ p Λ ¯ p and Measurement of Λ p Λ p Cross Section

    Usingmore » ( 10.087 ± 0.044 ) × 10 9 J / ψ events collected with the BESIII detector at the BEPCII storage ring, the processes Λ p Λ p and Λ ¯ p Λ ¯ p are studied, where the Λ / Λ ¯ baryons are produced in the process J / ψ Λ Λ ¯ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in 0.9 cos θ Λ / Λ ¯ 0.9 are measured to be σ ( Λ p Λ p ) = ( 12.2 ± 1.6 stat ± 1.1 syst ) and σ ( Λ ¯ p Λ ¯ p ) = ( 17.5 ± 2.1 stat ± 1.6 syst ) mb at the Λ / Λ ¯ momentum of 1.074 GeV / c within a range of ± 0.017 GeV / c , where the θ Λ / Λ ¯ are the scattering angles of the Λ / Λ ¯ in the Λ p / Λ ¯ p rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for Λ p Λ p , and a strong forward peak for Λ ¯ p Λ ¯ p . We present an approach to extract the total elastic cross sections by extrapolation. The study of Λ ¯ p Λ ¯ p represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction. Published by the American Physical Society 2024« less
  4. Search for the production of deuterons and antideuterons in e + e annihilation at center-of-mass energies between 4.13 and 4.70 GeV

    Usingmore » a data sample of e + e collision data corresponding to an integrated luminosity of 19 fb 1 collected with the BESIII detector at the BEPCII collider, we search for the production of deuterons and antideuterons via e + e p p π d ¯ + c . c . for the first time at center-of-mass energies between 4.13 and 4.70 GeV. No significant signal is observed and the upper limit of the e + e p p π d ¯ + c . c . cross section is determined to be from 9.0 to 145 fb depending on the center-of-mass energy at the 90% confidence level. Published by the American Physical Society 2024« less
  5. Measurement of e + e η J / ψ cross section from s = 3.808 GeV to 4.951 GeV

    Using dmore » ata samples with an integrated luminosity of 22.42 fb 1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the e + e η J / ψ process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with ψ ( 4040 ) , two additional resonances, and a nonresonant component are performed. The mass and width of the first additional state are ( 4219.7 ± 2.5 ± 4.5 ) MeV / c 2 and ( 80.7 ± 4.4 ± 1.4 ) MeV , respectively, consistent with the ψ ( 4230 ) . For the second state, the mass and width are ( 4386 ± 13 ± 17 ) MeV / c 2 and ( 177 ± 32 ± 13 ) MeV , respectively, consistent with the ψ ( 4360 ) . The first uncertainties are statistical, and the second ones are systematic. The statistical significance of ψ ( 4040 ) is 8.0 σ and those for ψ ( 4230 ) and ψ ( 4360 ) are more than 10.0 σ . Published by the American Physical Society 2024« less
  6. Evidence of the singly Cabibbo suppressed decay Λ c + p π 0

    Evidence formore » the singly Cabibbo suppressed decay Λ c + p π 0 is reported for the first time with a statistical significance of 3.7 σ based on 6.0 fb 1 of e + e collision data collected at center-of-mass energies between 4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider. The absolute branching fraction of Λ c + p π 0 is measured to be ( 1.5 6 0.58 + 0.72 ± 0.20 ) × 10 4 . Combining with the branching fraction of Λ c + n π + , ( 6.6 ± 1.3 ) × 10 4 , the ratio of the branching fractions of Λ c + n π + and Λ c + p π 0 is calculated to be 3.2 1.2 + 2.2 . As an important input for the theoretical models describing the decay mechanisms of charmed baryons, our result indicates that the nonfactorizable contributions play an essential role and their interference with the factorizable contributions should not be significant. In addition, the absolute branching fraction of Λ c + p η is measured to be ( 1.63 ± 0.3 1 stat ± 0.1 1 syst ) × 10 3 . Published by the American Physical Society 2024« less
  7. First Observation of a Three-Resonance Structure in e + e Nonopen Charm Hadrons

    We repormore » t the measurement of the inclusive cross sections for e + e nOCH (where nOCH denotes non-open charm hadrons) with improved precision at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe three resonances: R ( 3760 ) , R ( 3780 ) , and R ( 3810 ) with significances of 8.1 σ , 13.7 σ , and 8.8 σ , respectively. The R ( 3810 ) state is observed for the first time, while the R ( 3760 ) and R ( 3780 ) states are observed for the first time in the nOCH cross sections. Two sets of resonance parameters describe the energy-dependent line shape of the cross sections well. In set I [set II], the R ( 3810 ) state has mass ( 3805.7 ± 1.1 ± 2.7 ) [ ( 3805.7 ± 1.1 ± 2.7 ) ] MeV / c 2 , total width ( 11.6 ± 2.9 ± 1.9 ) [ ( 11.5 ± 2.8 ± 1.9 ) ] MeV , and an electronic width multiplied by the nOCH decay branching fraction of ( 10.9 ± 3.8 ± 2.5 ) [ ( 11.0 ± 3.4 ± 2.5 ) ] eV . In addition, we measure the branching fractions B [ R ( 3760 ) nOCH ] = ( 25.2 ± 16.1 ± 30.4 ) % [ ( 6.4 ± 4.8 ± 7.7 ) % ] and B [ R ( 3780 ) nOCH ] = ( 12.3 ± 6.6 ± 8.3 ) % [ ( 10.4 ± 4.8 ± 7.0 ) % ] for the first time. The R ( 3760 ) state can be interpreted as an open-charm (OC) molecular state, but containing a simple four-quark state component. The R ( 3810 ) state can be interpreted as a hadrocharmonium state. Published by the American Physical Society 2024« less
  8. Determination of Spin-Parity Quantum Numbers of X ( 2370 ) as 0 + from J / ψ γ K S 0 K S 0 η

    Bmore » ased on ( 10 087 ± 44 ) × 10 6 J / ψ events collected with the ESIII detector, a partial wave analysis of the decay J / ψ γ K S 0 K S 0 η is performed. The mass and width of the X ( 2370 ) are measured to be 2395 ± 11 ( stat ) 94 + 26 ( syst ) MeV / c 2 and 188 17 + 18 ( stat ) 33 + 124 ( syst ) MeV , respectively. The corresponding product branching fraction is [ J / ψ γ X ( 2370 ) ] × [ X ( 2370 ) f 0 ( 980 ) η ] × [ f 0 ( 980 ) K S 0 K S 0 ] = ( 1.31 ± 0.22 ( stat ) 0.84 + 2.85 ( syst ) ) × 10 5 . The statistical significance of the X ( 2370 ) is greater than 11.7 σ and the spin parity is determined to be 0 + for the first time. The measured mass and spin parity of the X ( 2370 ) are consistent with the predictions of the lightest pseudoscalar glueball. Published by the American Physical Society 2024« less
  9. Measurements of Born cross sections for e + e Λ c + Λ ¯ c ( 2595 ) + c . c . and e + e Λ c + Λ ¯ c ( 2625 ) + c . c . at s = 4918.0 and 4950.9 MeV

    Usingmore » e + e collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of e + e Λ c + Λ ¯ c ( 2595 ) + c . c . and e + e Λ c + Λ ¯ c ( 2625 ) + c . c . are measured for the first time at center-of-mass energies of s = 4918.0 and 4950.9 MeV. Nonzero cross sections are observed very close to the production threshold. The measured Born cross sections of e + e Λ c + Λ ¯ c ( 2625 ) + c . c . are about 2–3 times greater than those of e + e Λ c + Λ ¯ c ( 2595 ) + c . c . , providing the similar behavior as semileptonic decays of Λ b 0 , but different behavior from that in the hadronic decays of Λ b 0 . The Born cross sections are 15.6 ± 3.1 ± 0.9 pb and 29.4 ± 3.7 ± 2.7 pb for e + e Λ c + Λ ¯ c ( 2595 ) + c . c . , and are 43.4 ± 4.0 ± 4.1 pb and 76.8 ± 6.5 ± 4.2 pb for e + e Λ c + Λ ¯ c ( 2625 ) + c . c . at s = 4918.0 and 4950.9 MeV, respectively. Based on the polar angle distributions of the Λ ¯ c ( 2625 ) and Λ c ( 2625 ) + , the form-factor ratios | G E | 2 + 3 | G M | 2 / | G C | are determined for e + e Λ c + Λ ¯ c ( 2625 ) + c . c . for the first time, which are 5.95 ± 4.07 ± 0.15 and 0.94 ± 0.32 ± 0.02 at s = 4918.0 and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic. Published by the American Physical Society 2024« less
  10. Search for η c ( 2 S ) π + π η c and η c ( 2 S ) π + π K S 0 K ± π decays

    Bmore » ased on ( 27.12 ± 0.14 ) × 10 8 ψ ( 2 S ) events collected by the ESIII detector, we search for the decay η c ( 2 S ) π + π η c via ψ ( 2 S ) γ η c ( 2 S ) . No significant signal is observed, and the upper limit on the product branching fraction ( ψ ( 2 S ) γ η c ( 2 S ) ) × ( η c ( 2 S ) π + π η c ) is determined to be 2.21 × 10 5 at the 90% confidence level. In addition, the η c ( 2 S ) π + π K S 0 K ± π decay is studied via ψ ( 2 S ) γ η c ( 2 S ) and is observed with a statistical significance of 10 σ for the first time. The branching fraction of η c ( 2 S ) π + π K S 0 K ± π is determined to be ( 1.33 ± 0.11 ± 0.40 ± 0.95 ) × 10 2 , where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the quoted ( ψ ( 2 S ) γ η c ( 2 S ) ) . Published by the American Physical Society 2024« less
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