Future Colliders

Abstract:

A spin-parity 1+ρ{variant}π enhancement is observed for the 3π mass spectrum in the reaction K-p → Σ-π+π+π- where events with a small (K- → Σ-) momentum transfer are selected. The mass (1040 MeV) and width (230 MeV) of this enhancement are reminiscent of the A1 → ρ{variant}π bump which has mainly been observed in the diffractive-like processes. The cross section for this enhancement at 4.15 GeV/c incident K- momentum is (3.6 ± 0.5) μb. © 1977.

Abstract:

π - ω interference is studied in the reactions K- p → π+ π- (Λ0, ε{lunate}) at 4.2 GeV/c using data from a high statistics experiments in the CERN 2m HBC. The phenomenon is analysed in terms of the conventional formalism as well as in terms of a new model for π - ω interference proposed by Earles and Srivastava. Satisfactory agreement with the data is found for both models. The rate of ω → 2π obtained in the latter model is in agreement with the VMD (Vector Meson Dominance) prediction for ω → γ → ρ{variant} → 2π. © 1977.

Abstract:

A search for new particles that decay into top quark pairs (ttbar) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 4.7 fb^-1 of proton-proton (pp) collision data collected at a center-of-mass energy sqrt(s)=7 TeV. In the ttbar --> WbWb decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The ttbar system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the ttbar invariant mass spectrum is performed. No evidence for a ttbar resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z' resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z' resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with Gamma/m = 15.3%. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.07 TeV.