First absolute measurement of charmed baryon semi-leptonic decay rate at threshold by the BESIII experiment in Beijing

Published: 2015-12-10
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In the issue of the Physical Review Letters (PRL) dated on November 27th, 2015, a research, performed at the Beijing Spectrometer (BESIII) experiment, was reported on the first absolute measurement of charmed baryon semi-leptonic decay based on Λ_c-pair threshold data. The PRL reviewers commented that "... This measurement provides important data to model the phenomenology of hadrons and which go on to be used in current and future collider experiments. ...". Major contributions to this work were made by scientists of University of Chinese Academy of Sciences and the Beijing Institute of Petrochemical Technology.

Since theoretical predictions of weak interactions are relatively simple and reliable, weak decay process becomes highly important for particle physicists both to obtain information of internal structure of particles and to sensitively check the standard model. Λ_c is the lightest charmed baryon. It consists of 3 quarks (u, d, c), where c quark is heavier than u and d quarks. However, konwledge on the mechanism of the distribution and movement of these quarks inside Λ_c is limited, becasue of lackness of precise experimental data.

Based on this background, in 2014, about 500/pb electron-position annihilation data at Λ_c-pair threshold was collected by BESIII. The research team implemented the missing-neutrino technique to analyze this unique threshold data, and measured the absolute branching fraction of Λ_c⁺->Λe⁺ν_e.

This work is the first publication in research field of Λ_c⁺ decays at Beijing Spectrometer experiment since it debuted 30 years ago. It helps physicists to reveal the internal structure of Λ_c and to understand the asymmetry between matter and anti-matter in the universe. The research team expects more exciting results in research field of Λ_c⁺ decays.

Paper link： http://dx.doi.org/10.1103/PhysRevLett.115.221805

By Lv Xiaoru