UC Riverside

A search for the pair production of heavy vector-like partners T$$\mathrm {T}$$ and B$$\mathrm {B}$$ of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton–proton collisions at s=13Te$$\sqrt{s} = 13\,\text {Te}\text {V} $$. The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9fb-1$$\,\text {fb}^{-1}$$. Final states studied for TT¯$$\mathrm {T} \overline{\mathrm {T}} $$ production include those where one of the T$$\mathrm {T}$$ quarks decays via T→tZ$$\mathrm {T} \rightarrow \mathrm {t}\mathrm {Z}$$ and the other via T→bW$$\mathrm {T} \rightarrow \mathrm {b}\mathrm {W}$$, tZ$$\mathrm {t}\mathrm {Z}$$, or tH$$\mathrm {t}\mathrm {H} $$, where H$$\mathrm {H}$$ is a Higgs boson. For the BB¯$$\mathrm {B} \overline{\mathrm {B}} $$ case, final states include those where one of the B$$\mathrm {B}$$ quarks decays via B→bZ$$\mathrm {B} \rightarrow \mathrm {b}\mathrm {Z}$$ and the other B→tW$$\mathrm {B} \rightarrow \mathrm {t}\mathrm {W}$$, bZ$$\mathrm {b}\mathrm {Z}$$, or bH$$\mathrm {b}\mathrm {H} $$. Events with two oppositely charged electrons or muons, consistent with coming from the decay of a Z$$\mathrm {Z}$$ boson, and jets are investigated. The number of observed events is consistent with standard model background estimations. Lower limits at 95% confidence level are placed on the masses of the T$$\mathrm {T}$$ and B$$\mathrm {B}$$ quarks for a range of branching fractions. Assuming 100% branching fractions for T→tZ$$\mathrm {T} \rightarrow \mathrm {t}\mathrm {Z}$$, and B→bZ$$\mathrm {B} \rightarrow \mathrm {b}\mathrm {Z}$$, T$$\mathrm {T}$$ and B$$\mathrm {B}$$ quark mass values below 1280 and 1130Ge$$\,\text {Ge}\text {V}$$, respectively, are excluded.