Mass of the Up Quark

"The conclusion to draw if m_u were to vanish, would be that it is meaningless to truncate the chiral series at low orders, so that the success of the eightfold way cannot be understood within QCD. In effect, the proposal thus merely replaces one puzzle by the other. The work done on the lattice should close this chapter, confirming that a massless u-quark represents an interesting way not to understand this world: none of the lattice results is consistent with m_u = 0. In particular, the MILC collaboration rules this solution out at 10 σ . Nature solves the strong CP problem differently."

Taken from Leutwyler