Λc is the lightest baryon, which consists of three quarks, a heavy quark (c) and two light quarks (u, d). But scientists do not fully understand the specific distribution of quarks within Λc and the corresponding operating mechanism. Almost all Λc decay has weak force participation, its research can be used to test the weak interaction theory, and help us to understand the internal quark distribution in Λc. In addition, the study on the decay properties of Λc will help us to further understand the heavy taste baryon spectroscopy and its decay properties due to the transition of high-excited baryons and Λb baryons containing the quark to Λc. (Beijing spectrometer III experiment, text source of the Chinese Academy of Sciences Institute of High Energy Physics) Since 1979, when the baryon Λc was discovered by the MARKII experiment, most of the experimental studies on Λc were carried out more than twenty years ago. The Λc → pK? Πdecay was used as a reference to study the branch ratio of hadronic decay. However, due to the more or less reliance on the model assumptions, experimental measurements of the Λc → pK? Πbranching ratio are not accurate. This leads to great uncertainty in the overall result of the Λc decay branch ratio. After the unremitting efforts of researchers at Beijing Electron Positron Collider II, Beijing spectrometer III experiment successfully accumulated positive and negative electron annihilation data of 567pb? 1 at the mass center energy of 4.599GeV in 2014. The energy point is Λc Λc- higher than the mass threshold of about 26MeV, which greatly exceeds the maximum energy of 4.2GeV designed by the Beijing Electron Positron Collider II. At this energy, Λc and Λc- are generated in pairs, and no additional energy produces any other accompanying hadrons. Beijing Spectrometer III experiment Based on these data samples, we used the double labeling technique of fully reconstructed Λc Λc-pairs to measure the hadronic decay branch ratio of Λc. The advantage of this measurement method is that it does not depend on the assumption of Λc Λc- on the cross-section or its decay model and does not require input information such as data integral brightness, which we call absolute branch ratio measurement. Beijing spectrometer III experiment combined the twelve major Hadron decays of Λc with global fitting to improve the accuracy. The branching ratio of Λc → pK π was measured as B (Λc → pK π) = (5.84 ± 0.27 ± 0.23)%. This is the first time that Λc has discovered that the absolute branching ratio of Λc → pK? Πis precisely measured at the threshold in the world for the first time in more than three decades. In addition, based on the threshold data of 2015 Beijing Spectrometer III experiment, the absolute branching ratio of semi-light decay Λc → Λc νe is measured for the first time in the world by using the method of losing neutrino mass, and the accuracy of the result is greatly improved. This experimental measurement is of important guiding significance for understanding the decay lifetime of quarks containing quarks. Related researchers will continue their efforts to tap the potential of Beijing Spectrometer III experiment in Λc research. We are looking forward to publishing more related research results from Λc.
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August 28, 2019