T mesons are hypothetical mesons composed of a top quark and either an up (T0), down (T+), strange (T+
s) or charm antiquark (T0
c). Because of the top quark's short lifetime, T mesons are not expected to be found in nature. The combination of a top quark and top antiquark is not a T meson, but rather toponium. Each T meson has an antiparticle that is composed of a top antiquark and an up (T0), down (T−), strange (T−
s) or charm quark (T0
c) respectively.