Determination of light quark masses from {eta}{yields}3{pi}{sup 0}

We provide a model-independent determination of the quantity B{sub 0}(m{sub d}-m{sub u}). Our approach rests only on chiral symmetry and data from the decay of the eta into three neutral pions. Since the low-energy prediction at next-to-leading order fails to reproduce the experimental results, we keep the strong interaction correction as an unknown parameter. As a first step, we relate this parameter to the quark mass difference using data from the Dalitz plot. A similar relation is obtained using data from the decay width. Combining both relations we obtain B{sub 0}(m{sub d}-m{sub u})=(4495{+-}440) MeV{sup 2}. The preceding value, combined with lattice determinations, leads to the values m{sub u}(2 GeV)=(2.9{+-}0.8) MeV and m{sub d}(2 GeV)=(4.7{+-}0.8) MeV.