Recent results from OKA setup at U-70 synchrotron

Abstract

Abstract Several radiative decays are under study by OKA setup at U-70 synchrotron. First, the radiative decay K + → µ + νγ(K µ2γ ) is studied on statistics of about 95K events for 25 MeV < E γ * < 150 MeV. A clear destructive interference between bremsstrahlung and structure dependent SD − term is observed. As a result, the vector and axial-vector form factors difference is measured: F V − F A = 0.134 ± 0.021(stat.) ± 0.027(syst.) which is 2.3 σ away from χP T O(p 4). Moreover, the decay K + → π + π − π + γ is studied on statistics of about 450 events for 30 Mev < E γ * < 70 Mev. The total and differential branching fractions of the decay are measured. Br(K + → π + π − π + γ) = (7.1±0.4(stat.)±0.3(syst.))·10−6 to be compared with χP T O(p 4) (6.65 ± 0.05) · 10−6. In addition, a search for an up-down photon asymmetry with respect to the hadronic system decay plane is performed.