Odderon

In particle physics, the odderon corresponds to an elusive family of odd-gluon states, dominated by a three-gluon state. When protons collide elastically with other protons or with anti-protons at high energies, gluons are exchanged. Exchanging an even number of gluons is a crossing-even part of elastic proton–proton and proton–antiproton scattering, while odderon exchange (i.e. exchange of odd number of gluons) corresponds to a crossing-odd term in the elastic scattering amplitude. In turn, the odderon's crossing-odd counterpart is the pomeron.^{[clarification needed]}

It took about 48 years to find a definite signal of odderon exchange.^[2]