Lattice study of flavor SU(3) breaking in hyperon beta decay

We present a quenched lattice calculation of all six form factors: vector [f1(q2)], weak-magnetism [f2(q2)], induced scalar [f3(q2)], axial-vector [g1(q2)], weak electricity [g2(q2)], and induce pseudoscalar [g3(q2)] form factors, in hyperon semileptonic decay Ξ0→Σ+lν̄ using domain wall fermions. The q2 dependences of all form factors in the relatively low q2 region are examined in order to evaluate their values at zero momentum transfer. The Ξ0→Σ+ transition is highly sensitive to flavor SU(3) breaking since this decay corresponds to the direct analogue of neutron beta decay under the exchange of the down quark with the strange quark. The pattern of flavor SU(3) breaking effects in the hyperon beta decay is easily exposed in a comparison to results for neutron beta decay. We measure SU(3)-breaking corrections to f1(0), f2(0)/f1(0), and g1(0)/f1(0). A sign of the leading-order corrections, of which the size is less than a few percent, on f1(0) is likely negative, while f2(0)/f1(0) and g1(0)/f1(0) receive positive corrections of order 16% and 5%, respectively. The observed pattern of the deviation from the values in the exact SU(3) limit does not support some of the model estimates. We show that there are nonzero second-class form factors in the Ξ0→Σ+ decay, measuring f3(0)/f1(0)=0.14(9) and g2(0)/g1(0)=0.68(18), which are comparable to the size of first-order SU(3) breaking. It is also found that the SU(3) breaking effect on g3(0)/g1(0) agrees with the prediction of the generalized pion-pole dominance.