Abstract
Abstract From 56 days of data taking in 2002, the NA48/1 experiment observed 6316 Ξ 0 → Σ + e − ν ¯ e candidates (with the subsequent Σ + → p π 0 decay) and 555 Ξ 0 ¯ → Σ + ¯ e + ν e candidates with background contamination of 215 ± 44 and 136 ± 8 events, respectively. From these samples, the branching ratios BR ( Ξ 0 → Σ + e − ν ¯ e ) = ( 2.51 ± 0.03 stat ± 0.09 syst ) × 10 −4 and BR ( Ξ 0 ¯ → Σ + ¯ e + ν e ) = ( 2.55 ± 0.14 stat ± 0.10 syst ) × 10 −4 were measured allowing the determination of the CKM matrix element | V us | = 0.209 −0.028 +0.023 . Using the Particle Data Group average for | V us | obtained in semileptonic kaon decays, we measured the ratio g 1 / f 1 = 1.20 ± 0.05 of the axial-vector to vector form factors.
Highlights
The study of hadron β-decays gives important information on the interplay between the weak interaction and the hadronic structure determined by the strong interaction
In the exact SU(3) symmetry approximation, the ratio between the axial-vector form factor g1 and the vector form factor f1 for Ξ0 β-decay is equal to the one for the decay n → pe−νe
Precise tests of SU(3) symmetry breaking effects calculations in semileptonic hyperon decays are important in connection with the determination of Vus, independently from kaon decays
Summary
The study of hadron β-decays gives important information on the interplay between the weak interaction and the hadronic structure determined by the strong interaction. Mostly present at large |rCOG| values, exhibit a peak in the pπ0 invariant mass distribution, consistent with the Σ+ mass (see Fig. 5) These events are genuine Ξ0 → Σ+e−νe decays, they were subtracted from the final sample in order to minimize uncertainties associated with their production yield and acceptance calculation. 6 Ξ0 → Σ+e−νe branching ratio The determination of the Ξ0 → Σ+e−νe branching ratio was obtained from the background subtracted number of good events for signal and normalization, the corresponding acceptance values, the L2 trigger efficiency measured with respect to the L1 one and the normalization branching ratios [18]
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