Gell-Mann–Okubo mass formula

In physics, the Gell-Mann–Okubo mass formula provides a sum rule for the masses of hadrons within a specific multiplet, determined by their isospin (I) and strangeness (or alternatively, hypercharge) M = a 0 + a 1 Y + a 2 [ I ( I + 1 ) − 1 4 Y 2 ] , {\displaystyle M=a_{0}+a_{1}Y+a_{2}\left[I\left(I+1\right)-{\frac {1}{4}}Y^{2}\right],} where a0, a1, and a2 are free parameters. The rule was first formulated by Murray Gell-Mann in 1961 and independently proposed by Susumu Okubo in 1962.

Source: Wikipedia — Gell-Mann–Okubo mass formula (CC BY-SA 4.0)