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Register a new userMeasurement of the absolute branching fraction for $Lambda^+_{c}to Lambda e^+ u_e$
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We report the first absolute measurement of the branching fraction of $Lambda^+_{c}rightarrow Lambda e^+ u_e$. This measurement is based on 567 pb$^{-1}$ of $e^+e^-$ annihilation data produced at $sqrt{s}=4.599$ GeV, which is just above the $Lambda^+_cbar{Lambda}^-_c$ threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be $mathcal B({Lambda^+_crightarrow Lambda e^+ u_e})=(3.63pm0.38({rm stat})pm0.20({rm syst}))%$, representing a more than twofold improvement in precision upon previously published results. As the branching fraction for $Lambda^+_{c}rightarrow Lambda e^+ u_e$ is the benchmark for those of other $Lambda^+_c$ semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.
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Based on an $e^+e^-$ collision data sample corresponding to an integrated luminosity of 567$,rm{pb}^{-1}$ taken at the center-of-mass energy of $sqrt{s} = 4.6$ GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay $Lambda_{c}^{+} to Lambda + X$ to be $mathcal{B}(Lambda_{c}^{+} to Lambda + X)=(38.2^{+2.8}_{-2.2}pm0.8)%$ using the double-tag method, where $X$ refers to any possible final state particles. In addition, we search for direct CP violation in the charge asymmetry of this inclusive decay for the first time, and obtain $mathcal{A}_{CP} equiv frac{mathcal{B}(Lambda_{c}^{+} to Lambda + X)-mathcal{B}(bar{Lambda}_{c}^{-} to bar{Lambda} + X)}{mathcal{B}(Lambda_{c}^{+} to Lambda + X)+mathcal{B}(bar{Lambda}_{c}^{-} to bar{Lambda} + X)} = (2.1^{+7.0}_{-6.6}pm1.4)%$, a statistically limited result with no evidence of CP violation.
We report the first measurement of the absolute branching fraction for $Lambda^+_{c}rightarrow Lambda mu^+ u_{mu}$. This measurement is based on a sample of $e^+e^-$ annihilation data at a center-of-mass energy of $sqrt{s}=4.6$ GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb$^{-1}$. The branching fraction is determined to be $mathcal B({Lambda^+_crightarrow Lambda mu^+ u_{mu}})=(3.49pm0.46({rm stat})pm0.27({rm syst}))%$. In addition, we calculate the ratio $mathcal{B}(Lambda^+_crightarrow Lambda mu^+ u_{mu})/mathcal{B}(Lambda^+_crightarrow Lambda e^+ u_{e})$ to be $0.96pm0.16({rm stat})pm0.04({rm syst})$.
The absolute branching fraction of $Lambda to p mu^- bar{ u}_{mu}$ is reported for the first time based on an $e^+e^-$ annihilation sample of ten billion $J/psi$ events collected with the BESIII detector at $sqrt{s}=3.097$ GeV. The branching fraction is determined to be ${mathcal B}(Lambda to pmu^- bar{ u}_{mu}) = [1.48pm0.21(rm stat) pm 0.08(rm syst)]times 10^{-4}$, which is a significant improvement in precision over the previous indirect measurements. Combining this result with the world average of ${mathcal B}(Lambda to p e^- bar{ u}_{e})$, we obtain the ratio, $frac{Gamma(Lambda to p mu^- bar{ u}_{mu})}{Gamma(Lambda to p e^- bar{ u}_{e})}$, to be $0.178 pm 0.028$, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of $Lambda to p mu^- bar{ u}_{mu}$ and $bar{Lambda} to bar{p} mu^+ u_{mu}$ is also determined, and no evidence for $CP$ violation is found.
Using a data set of 6.32 fb$^{-1}$ of $e^+ e^-$ annihilation data collected with the BESIII detector at center-of-mass energies between 4178 and 4226 MeV, we have measured the absolute branching fraction of the leptonic decay $D_s^+ to tau^+ u_{tau}$ via $tau^+ to e^+ u_e bar{ u}_{tau}$ to be $mathcal{B}_{D_s^+ to tau^+ u_{tau}}=(5.27pm0.10pm0.12)times10^{-2}$, where the first uncertainty is statistical and the second is systematic. Combining with $f_{D_s^+}$ from Lattice quantum chromodynamics calculations or the $|V_{cs}|$ from the CKMfitter group, we extract $|V_{cs}|=0.978pm0.009pm0.012$ and $f_{D_s^+}= (251.1pm2.4pm3.0)$ MeV, respectively. These results are the most precise to date. Combining our result with the world averages of $mathcal{B}_{D_s^+ to tau^+ u_{tau}}$ and $mathcal{B}_{D_s^+ to mu^+ u_{mu}}$, we obtain the ratio of the branching fractions $mathcal{B}_{D_s^+ to tau^+ u_{tau}} / mathcal{B}_{D_s^+ to mu^+ u_{mu}} = 9.72pm0.37$, which is consistent with the standard model prediction of lepton flavor universality.
Using 2.93 fb$^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at a center-of-mass energy of 3.773 GeV, we measure the absolute branching fractions of the decays $D^0to K^-e^+ u_e$ and $D^+to bar K^0 e^+ u_e$ to be $(3.567pm0.031_{rm stat}pm 0.025_{rm syst})%$ and $(8.68pm0.14_{rm stat}pm 0.16_{rm syst})%$, respectively. Starting with the process $e^+e^-to Dbar{D}$, a new reconstruction method is employed to select events that contain candidates for both $Dto bar Ke^+ u_e$ and $bar Dto Ke^-bar u_e$ decays. The branching fractions reported in this work are consistent within uncertainties with previous BESIII measurements that selected events containing $Dto bar Ke^+ u_e$ and hadronic $bar D$ decays. Combining our results with the lifetimes of the $D^0$ and $D^+$ mesons and the previous BESIII measurements leads to a ratio of the two decay partial widths of $frac{bar Gamma_{D^0to K^{-}e^+ u_{e}}}{bar Gamma_{D^{+}to bar K^{0}e^+ u_{e}}}=1.039pm0.021$. This ratio supports isospin symmetry in the $D^0to K^-e^+ u_e$ and $D^+to bar K^0 e^+ u_e$ decays within $1.9sigma$.
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