In strong decays, the products will contain the same quarks and antiquarks that have existed in the original particle, possibly with the addition of one or more

In strong decays, the products will contain the same quarks and antiquarks that have existed in the original particle, possibly with the addition of one or more quark-antiquark pairs that have been generated during the decay. In weak decays, one or more of the original quarks or antiquarks will be converted in a quark or antiquark with a different flavor, which is a process that has a low probability of happening, so the weak decays happen less frequently, therefore the hadrons that can decay only through weak decays have a lifetime that is many orders of magnitude greater than the hadrons that can decay through strong decays (or electromagnetic decays, i.e. annihilation of quarks with the corresponding antiquarks). D+ is c quark + d antiquark, D0 is c quark + u antiquark Tcc(3875)+ is 2 c quarks + d antiquark + u antiquark Therefore the 4 quarks/antiquarks in Tcc(3875)+ are the same as the 4 quarks/antiquarks in D0 + D+. So this is a strong decay, because no quark or antiquark is converted into another kind of quark or antiquark. For the Tbb- tetraquark, its composition would allow a similar strong decay into two b-quark + u or d antiquark hadrons, except that its binding energy is so great that the mass of the Tbb- tetraquark is smaller than the sum of the masses of the hadrons that would be produced during a strong decay (it is also smaller than the sum of masses of the hadrons that could be produced by an electromagnetic decay, see https://www.sciencedirect.com/science/article/pii/S0370269319307956 https://www.sciencedirect.com/science/article/pii/S037026931... ). This forbids the strong decay and the electromagnetic decay, so the only admissible decay must be weak, where one of the b quarks will be converted into another kind of quark.