The isospin breaking effect on baryons with Nf=2 domain wall fermions

We study the isospin breaking effect on octet baryons. Using the two-flavor dynamical domain-wall QCD configurations combined with the quenched non-compact QED configurations, the electromagnetic mass splittings between isomultiplets (p, n), (Sigma^+, Sigma^0, Sigma^-), (Xi^0, Xi^-) are investigated. We evaluate the main source of statistical fluctuations in the two-point correlation function, and find that the elimination of O(e) fluctuation (e: the QED charge) is essential to extract the signal. Preliminary results for $m_p - m_n$ as well as other mass splittings are presented. Possible origin of systematic uncertainty is also discussed.