 R-parity

R-parity is the multiplicative number $R_p=(-1{)}^{3(B-L)+2s}$, where $B$ is baryon number, $L$ is lepton number and $s$ is spin. Standard Model particles are even and their superpartners are odd.

If conserved, an initially even state produces an even number of odd states, and the lightest odd state is stable. A neutral stable state may escape a detector and give missing transverse momentum. Stability alone does not establish its cosmological relic abundance.^[ref]