The inclusive cross section for top quark pair production is measured in proton-proton collisions at s√=7s=7 and 8 TeV, corresponding to 5.0 and 19.7 fb−1, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributions related to identified b quark jets and other jets in the event. The measured cross section values are 173.6 ± 2.1(stat)− 4.0+ 4.5(syst) ± 3.8(lumi)pb at s√=7s=7 TeV, and 244.9 ± 1.4(stat)− 5.5+ 6.3(syst) ± 6.4(lumi)pb at s√=8s=8 TeV, in good agreement with QCD calculations at next-to-next-to-leading-order accuracy. The ratio of the cross sections measured at 7 and 8 TeV is determined, as well as cross sections in the fiducial regions defined by the acceptance requirements on the two charged leptons in the final state. The cross section results are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, giving a best result of 173. 8− 1.8+ 1.7 GeV. The data at s√=8s=8 TeV are also used to set limits, for two neutralino mass values, on the pair production of supersymmetric partners of the top quark with masses close to the top quark mass.
A new baryon state is observed in the Λ0bπ+π− mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies s√=7,8 and 13TeV, corresponding to an integrated luminosity of 9fb−1. The mass and natural width of the new state are measured to be
where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Λ0b baryon mass. The new state is consistent with the first radial excitation of the Λ0b baryon, the Λb(2S)0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λb(5912)0 and Λb(5920)0 states are also reported.
The decays Λb0 → ψ(2S)pK− and Λb0 → J/ψπ+π−pK− are observed in a data sample corresponding to an integrated luminosity of 3 fb−1, collected in proton-proton collisions at 7 and 8 TeV centre-of-mass energies by the LHCb detector. The ψ(2S) mesons are reconstructed through the decay modes ψ(2S) → μ+μ− and ψ(2S) → J/ψπ+π−.The branching fractions relative to that of Λb0 → J/ψpK− are measured to be M(Λ0b)=5619.65±0.17±0.17 MeV/c2,M(Λb0)=5619.65±0.17±0.17 MeV/c2, where the uncertainties are statistical and systematic.