According to the preprint linked above they are hybrid equivalents of the proton or neutron. Protons and neutrons are made of up and down quarks. Protons are uu

According to the preprint linked above they are hybrid equivalents of the proton or neutron. Protons and neutrons are made of up and down quarks. Protons are uud, neutrons are ddu. (d have charge -1/3, u +2/3, so neutrons have no net charge, protons +1). There are three "generations" of quarks, each one heavier than the last but otherwise identical in properties. These are charm and strange followed by top and bottom. These new particles are a mix of generations: bds (bottom, down, strange). They are predicted by the Standard Model, but their detailed properties (particularly their branching ratios to various decays into other particles) will be slightly different in theories of "physics beyond the Standard Model", so by looking at them in detail, including a precision measurement of their masses, it may be possible to kill off some alternative theories.