Searches are performed for a low-mass dimuon resonance, X, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using a data sample corresponding to an integrated luminosity of 5.1 fb−1 and collected with the LHCb detector. The X bosons can either decay promptly or displaced from the proton-proton collision, where in both cases the requirements placed on the event and the assumptions made about the production mechanisms are kept as minimal as possible. The searches for promptly decaying X bosons explore the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible X widths considered above 20 GeV. The searches for displaced X → μ+μ− decays consider masses up to 3 GeV. None of the searches finds evidence for a signal and 90% confidence-level exclusion limits are placed on the X → μ+μ− cross sections, each with minimal model dependence. In addition, these results are used to place world-leading constraints on GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios.

Study of the ψ 2 (3823) and χ c1 (3872) states in B + → (J/ψπ + π −) K + decays The LHCb collaboration

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The interaction of silicon (Si) nanospheres (NSs) with a thin metal film is investigated numerically and experimentally by characterizing their forward scattering properties. A sharp resonant mode and a zero-scattering dip are found to be introduced in the forward scattering spectrum of a Si NS by putting it on a 50-nm-thick gold film. It is revealed that the sharp resonant mode arises from a new magnetic dipole induced by the electric dipole and its mirror image while the zero-scattering dip originates from the destructive interference between the new magnetic dipole and the original one together with its mirror image. A significant enhancement in both electric and magnetic fields is achieved at the contact point between the Si NS and the metal film. More interestingly, the use of a thin silver film can lead to vivid scattering light with different color indices. It is demonstrated that a small change in the surrounding environment of Si NSs results in the broadening of the resonant mode and the disappearance of the zero-scattering dip. Our findings indicate that dielectric-metal hybrid systems composed of semiconductor NSs and thin metal films act as attractive platforms on which novel nanoscale plasmonic devices can be realized.

The shape of the $$ {B}_s^0\to {D}_s^{\ast -}{\mu}^{+}{\nu}_{\mu } $$ B s 0 → D s ∗ − μ + ν μ differential decay rate is obtained as a function of the hadron recoil parameter using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb−1 collected by the LHCb detector. The $$ {B}_s^0\to {D}_s^{\ast -}{\mu}^{+}{\nu}_{\mu } $$ B s 0 → D s ∗ − μ + ν μ decay is reconstructed through the decays $$ {D}_s^{\ast -}\to {D}_s^{-}\gamma $$ D s ∗ − → D s − γ and $$ {D}_s^{-}\to {K}^{-}{K}^{+}{\pi}^{-} $$ D s − → K − K + π − . The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.