2022-12-08

BESIII recently reported the study of the Cabibbo-favored Semileptonic (SL) decay Λ_{c}^{+}->Λe^{+}ν_{e} [Phys. Rev. Lett. 129, 231803 (2022)], with the largest Λ_{c }threshold data sets collected at the center-of-mass energy region between 4.6 GeV and 4.7 GeV.

The study of Λ_{c} SL decays provides valuable information about weak and strong interactions in baryons containing a heavy quark. In particular, the SL decay Λ_{c}^{+}->Λe^{+}ν_{e} which is the dominant component in Λ_{c} SL decays, is the most interesting to measure. Its decay rate depends on the weak quark mixing Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vcs| and strong interaction effects parameterized by form factors describing the hadronic transition between the initial and the final baryons. Measurement of |Vcs| via Λ_{c}^{+}->Λe^{+}ν_{e} is an important consistency test for the standard model (SM) and a probe for new physics beyond the SM. Motivated by the measurements of the absolute branching fractions (BFs) for Λ_{c}^{+}->Λe^{+}ν_{e }and Λ_{c}^{+}->Λμ^{+}ν_{μ }by BESIII experiment, the first calculation of the BFs for Λ_{c}^{+}->Λl^{+}ν_{l} from the lattice quantum chromodynamics (LQCD) are available in 2017. The LQCD also investigated the internal dynamics and predicted the form factors and differential decay rates in Λ_{c}^{+}->Λe^{+}ν_{e} decay, followed by a series of other LQCD calculations in this sector. These theoretical works are important for understanding the decay mechanism in SL decays in the charmed baryon sector. However, there is no direct experimental data for testing and calibrating these calculations.

Using the 4.5/fb Λ_{c }threshold data sets collected with BESIII detector, we report an updated measurement of the absolute BF for Λ_{c}^{+}->Λe^{+}ν_{e} to be (3.56±0.11±0.07)%, which improves precision of the world average value more than threefold. Combing BF of Λ_{c}^{+}->Λe^{+}ν_{e} measured in this work, Λ_{c}^{+ }life time and the q^{2}-integrated rate predicted by LQCD, we determine |Vcs|=0.936±0.017±0.025, which is in consistent with |Vcs|=0.939±0.038 measured in D->K*l*^{+}ν* _{l}* decays within one standard deviation. Furthermore, by analyzing the dynamics of Λ

Figure 1. Comparison of form factors with LQCD calculations.

Figure 2. Comparison of the differential decay rates with LQCD predictions.

Further reading: https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.129.231803

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.231803