We present the first quenched lattice QCD study of the form factors relevant for the hyperon semileptonic decay Σ→nℓν. The momentum dependence of both axial and vector form factors is investigated and the values of all the form factors at zero-momentum transfer are presented. Following the same strategy already applied to the decay K→πℓν, the SU(3)-breaking corrections to the vector form factor at zero-momentum transfer, f(0), are determined with great statistical accuracy in the regime of the simulated quark masses, which correspond to pion masses above ≈0.7 GeV. Besides f(0) also the axial to vector ratio g(0)/f(0), which is relevant for the extraction of the CKM matrix element V, is determined with significant accuracy. Due to the heavy masses involved, a polynomial extrapolation, which does not include the effects of meson loops, is performed down to the physical quark masses, obtaining f(0)=-0.948±0.029 and g(0)/f(0)=-0.287±0.052, where the uncertainties do not include the quenching effect. Adding a recent next-to-leading order determination of chiral loops, calculated within the Heavy Baryon Chiral Perturbation Theory in the approximation of neglecting the decuplet contribution, we obtain f(0)=-0.988±0.029±0.040. Our findings indicate that SU(3)-breaking corrections are moderate on both f(0) and g(0). They also favor the experimental scenario in which the weak electricity form factor, g(0), is large and positive, and correspondingly the value of |g(0)/f(0)| is reduced with respect to the one obtained with the conventional assumption g(q)=0 based on exact SU(3) symmetry.
Nuclear Physics B
- Pub Date:
- January 2007
- High Energy Physics - Phenomenology;
- High Energy Physics - Experiment;
- High Energy Physics - Lattice
- final version to appear in Nucl. Phys. B