We report a branching fraction measurement of the singly Cabibbo-suppressed decay Λ+c → ΛK+ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span ...center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of 6.44 fb −1 . The branching fraction of Λ+c → ΛK+ relative to that of the Cabibbo-favored decay Λ+c → Λπ+ is measured to be R = B(Λ+c → ΛK+) / B(Λ+c → Λπ+) = (4.78±0.34±0.20)%. Combining with the world-average value of B(Λ+c → Λπ+), we obtain B(Λ+c → ΛK+) = (6.21±0.44±0.26±0.34) × 10 −4 . Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the Λ+c→Λπ+ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that nonfactorizable contributions have been underestimated in current models.
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Immunity acquired from infection or vaccination protects humans from symptomatic hepatitis E. However, whether the risk of hepatitis E virus (HEV) infection is reduced by the immunity remains ...unknown. To understand this issue, a cohort with 12 409 participants randomized to receive the hepatitis E vaccine Hecolin® or placebo were serologically followed up for 2 years after vaccination. About half (47%) of participants were initially seropositive. A total of 139 infection episodes, evidenced by four-fold or greater rise of anti-HEV level or positive seroconversion, occurred in participants who received three doses of treatment. Risk of infection was highest among the baseline seronegative placebo group participants (2.04%). Pre-existing immunity and vaccine-induced immunity lower the risk significantly, to 0.52% and 0.30%, respectively. In conclusion, both vaccine-induced and naturally acquired immunity can effectively protect against HEV infection.
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BFBNIB, DOBA, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UKNU, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The singly Cabibbo suppressed decay Λ + c → pη′ is measured using 4.5 fb −1 of e + e − collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at ...BEPCII. Evidence for Λ + c → pη′ with a statistical significance of 3.6σ is reported with a double-tag approach. The Λ + c → pη′ absolute branching fraction is determined to be (5.62 +2.46 −2.04 ±0.26)×10 −4 , where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of 1σ.
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This paper reports the study of D+s→τ+ν via τ+→π+¯ντ using a boosted decision tree method, with 7.33 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between ...4.128 and 4.226 GeV. The branching fraction of D+s→τ+ντ is determined to be (5.44±0.17stat±0.13syst)%. The product of the D+s decay constant fD+s and the Cabibbo-Kobayashi-Maskawa matrix element |Vcs| is fD+s|Vcs|=(248.3±3.9stat±3.1syst±1.0input) MeV. Combining with the |Vcs| value obtained from the Standard Model global fit or the fD+s from the lattice quantum chromodynamics, we determine |Vcs|=0.993±0.015stat±0.012syst±0.004input and fD+s=(255.0±4.0stat±3.2syst±1.0input) MeV. The first uncertainty is statistical, the second one is systematic and the third one is due to the input parameters, mainly the lifetime of D+s. All results obtained in this work supersede the BESIII previous results based on 6.32 fb−1 of e+e− collision data taken at center-of-mass energies between 4.178 and 4.226 GeV.
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