First Measurement of Form Factors of the DecayΞ0→Σ+e−

Abstract

We present the first measurement of the form factor ratios g(1)/f(1) (direct axial vector to vector), g(2)/f(1) (second class current), and f(2)/f(1) (weak magnetism) for the decay Xi(0)-->Sigma(+)e(-)nu macro(e) using the KTeV (E799) beam line and detector at Fermilab. From the Sigma(+) polarization measured with the decay Sigma(+)-->p pi(0) and the e(-)-nu; correlation, we measure g(1)/f(1) to be 1.32+/-(0.21)(0.17)(stat)+/-0.05(syst), assuming the SU(3)(f) (flavor) values for g(2)/f(1) and f(2)/f(1). Our results are all consistent with exact SU(3)(f) symmetry.

Hyperon semileptonic decay constants with flavor SU(3) symmetry breaking

“…However, the experimental data for HSDs show that flavor SU(3) symmetry is manifestly broken. For example, the ratio g 1 /f 1 = 1.21 ± 0.05 for the HSD process Ξ 0 → Σ + e − ν e measured by the KTeV collaboration [8,9] is equal to that of the neutron β decay (g 1 /f 1 = 1.2695 ± 0.0029) in flavor SU(3) symmetry. Thus, complete information on HSDs will furnish the pattern of flavor SU(3) symmetry breaking in nature.…”

“…On the other hand, hyperon semileptonic decays (HSDs) can also provide independent constraints on |V ud | and |V us | [6,7]. For last years, new experimental results for HSD have been reported: the KTeV collaboration first announced the measurement of the Ξ 0 → Σ + e − ν e decay [8] and determined the corresponding form factors [9] as f 2 (0)/f 1 (0) = 2.0 ± 1.2 stat ± 0.5 syst and g 1 (0)/f 1 (0) = 1.32 +0. 21 −0.17stat ± 0.05 syst .…”

Hyperon decay form factors in chiral perturbation theory

“…Refs. [1][2][3][4][5]). The transition matrix elements are parameterized in terms of three vector current and three axial current form factors.…”

“…In addition to the already mentioned vector form factor at zero momentum transfer, we also calculate further observables such as weak radii and the weak anomalous magnetic moments. Those observables have become measurable nowadays [2,3], and more results are expected from high-energy colliders in the future.…”

Hyperon vector form factor from2+1flavor lattice QCD

“…Using the best estimate of jV us j ¼ 0:2254ð6Þ with imposing CKM unitarity [33], we then predict the values jV us f 1 ð0Þj Ä!AE ¼ 0:2194ð8Þ V us ð15Þ f 1 and jV us f 1 ð0Þj AE!N ¼ 0:2186ð8Þ V us ð24Þ f 1 . The former is barely consistent with a single experimental result of jV us f 1 ð0Þj Ä!AE ¼ 0:209ð27Þ [34], albeit with its large experimental error. However, the latter is slightly deviated from the currently available experimental result of jV us f 1 ð0Þj AE!N ¼ 0:2282ð49Þ [4] due to reaching the value of f 1 ð0Þ with an accuracy of less than one percent.…”