The production of exclusive γγ→μ+μ− events in proton–proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb−1. The measurement is performed for a dimuon invariant mass of 12GeV<mμ+μ−<70GeV. The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions both with and without corrections for absorptive effects. 

An observation of the Λ_b ⁰→ψ(2S)Λ⁰ decay and a comparison of its branching fraction with that of the Λ_b ⁰→J/ψΛ⁰ decay has been made with the ATLAS detector in proton-proton collisions at s=8 TeV at the LHC using an integrated luminosity of 20.6 fb^-1. The J/ψ and ψ(2S) mesons are reconstructed in their decays to a muon pair, while the Λ⁰→ pπ^- decay is exploited for the Λ⁰ baryon reconstruction. The Λ_b ⁰ baryons are reconstructed with transverse momentum p_T>10 GeV and pseudorapidity |η|<2.1. The measured branching ratio of the Λ_b ⁰→ψ(2S)Λ⁰ and Λ_b ⁰J/ψΛ⁰ decays is G{cyrillic}(Λ_b ⁰→ψ(2S)Λ⁰/G{cyrillic}(Λ_b ⁰J/ψΛ⁰)=0.501±0.033(stat)±0.019(syst), lower than the expectation from the covariant quark model.

The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard-scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in t (t) over bar events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb(-1) of data recorded with the ATLAS detector at a centre-of-mass energy of root s = 8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.

A new scenario to realize negative refraction with a photonic-resonant vapor material that can exhibit both electric and magnetic responses via multilevel quantum coherence is suggested. Compared with the previous method of artificial composite metamaterial, where the mechanism was considered by means of classical electromagnetic theory and the materials produced have anisotropic millimetre-scale composite structures, the present scheme suggested within the framework of quantum optics can be used to design and fabricate isotropic negatively-refracting materials with atomic-scale microscopic structure units. Such an advantage may lead to a potentially important application in the techniques of superlens and perfect imaging.

High pressure electrical resistivity studies were carried out on the high temperature superconductor Nd1-xCaxBa2Cu3O7-delta for various calcium concentrations x = 0.00, 0.03, 0.06 and 0.10 obtained by the solid-state reaction method. The electrical resistivity study was performed using the four-probe technique with a Bridgman opposed anvil device. All four samples show an initial drastic fall in electrical resistivity up to a pressure of around 3 GPa that remains almost constant up to 8 GPa.