The BESIIICollaboration measured the absolute branching fraction of the, Λ⁺_c  → Λe ⁺ ν_e, decay with data set at the Λ+_c   Λ-c threshold (~4.6 GeV). This result is essential for understanding the theoretical model of charm baryon and provides important information for future collider experiments.  

The study of the weakly semileptonic decays plays an important role in probing the internal structure of particles and testing theoretical models with extremely high sensitivity, since calculating the weak interaction is relatively reliable. Λ_c is the lightest charmed baryon, and contains three quarks (c, u and d), with the c quark being the heaviest and the u and d quarks much lighter in an  isospin zero state. The distribution and dynamics of the three quarks inside the Λ_c  need dedicated theoretical models to describe them. The relevant theoretical research, however, is very limited at present, so this improved measurement will provide important input for theoretical research. 

The proposal to accumulate data at 4.6 GeV was approved by the BESIII collaboration in 2013, to get the high statistics, clean data sample necessary to study the decay properties of the Λ_c. A data sample of  approximately 500 pb-1 at 4.6 GeV was accumulated in 2014. Using double tag and the missing energy methods, careful analysis was performed and the absolute decay branching fraction of the Λ⁺_c  → Λe + ν_e decay was measured for the first time, in a model-independent way. This is the first Λ_c result at the Beijing Spectrometer experiment since it started its first run almost 30 years ago. This result will not only help us to better understand the internal structure of Λ_c and the weak and strong interactions of the Standard Model, but also to reveal the sources of matter-antimatter asymmetry in the universe. 

Under the title Measurement of the Absolute Branching Fraction for Λ⁺_c→Λe + ν_e, the first measurement of the semileptonic decay of the charmed baryonat the Beijing Spectrometer-III (BESIII) was published online by Physical Review Letters.   

              Absolute Measurement of Semileptonic Decay of Λ_c at BESIII (Image by BESIII Collaboration)