Seminarium Fizyki Jądra Atomowego
sala 1.01, ul. Pasteura 5
2026-10-29 (10:15) 
dr Varvara Batozskaya (NCBJ)
Semileptonic decays of baryons: testing the Standard Model with hyperons at the BESIII experiment
Seminarium zostanie wygłoszone w języku angielskim.
The seminar will be held in English.
Abstract: In the Standard Model, a quark can change its flavour only through the weak charged current. The strength of each transition is given by an element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The most precise test of the matrix's unitarity combines |Vud|, known from superallowed nuclear semileptonic decays, with |Vus|. However, the present |Vus| values from kaon and tau decays disagree with each other and both fall below the unitarity expectation. Semileptonic decays of hyperons, baryons containing a strange quark, off er an independent and theoretically clean way to determine |Vus|. They also give access to the form factors of the baryon weak current and test its symmetries. Until recently, however, the experimental input came from fi xed-target experiments more than 30 years ago.
With the large data sets from e+e- annihilation at the J/ψ resonance collected by the BESIII experiment, multidimensional analyses that use the polarisation and quantum entanglement of hyperon-antihyperon pairs give new insight into the hadronic structure of semileptonic decays. Using the world's largest J/psi dataset, BESIII has measured the fi rst absolute branching fractions of Lambda and charged Xi semileptonic decays. It has also measured the form-factor ratios of hyperons and antihyperons, including the fi rst determination of the weak-electricity coupling. Combined with lattice QCD calculations, this allows |Vus| to be extracted from hyperon decays for the fi rst time in more than 20 years.
The seminar will be held in English.
Abstract: In the Standard Model, a quark can change its flavour only through the weak charged current. The strength of each transition is given by an element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The most precise test of the matrix's unitarity combines |Vud|, known from superallowed nuclear semileptonic decays, with |Vus|. However, the present |Vus| values from kaon and tau decays disagree with each other and both fall below the unitarity expectation. Semileptonic decays of hyperons, baryons containing a strange quark, off er an independent and theoretically clean way to determine |Vus|. They also give access to the form factors of the baryon weak current and test its symmetries. Until recently, however, the experimental input came from fi xed-target experiments more than 30 years ago.
With the large data sets from e+e- annihilation at the J/ψ resonance collected by the BESIII experiment, multidimensional analyses that use the polarisation and quantum entanglement of hyperon-antihyperon pairs give new insight into the hadronic structure of semileptonic decays. Using the world's largest J/psi dataset, BESIII has measured the fi rst absolute branching fractions of Lambda and charged Xi semileptonic decays. It has also measured the form-factor ratios of hyperons and antihyperons, including the fi rst determination of the weak-electricity coupling. Combined with lattice QCD calculations, this allows |Vus| to be extracted from hyperon decays for the fi rst time in more than 20 years.