$\mathit Q{}\equiv\sqrt {({{\mathit m}^{2}}_{{{\mathit s}}}−{{\overline{\mathit m}}}{}^{2})/({{\mathit m}^{2}}_{{{\mathit d}}}−{{\mathit m}^{2}}_{{{\mathit u}}}) }$; ${{\overline{\mathit m}}}{}\equiv$ (${\mathit m}_{{{\mathit u}}}$ $+$ ${\mathit m}_{{{\mathit d}}})/$2