Single-photon light detection and ranging (lidar) offers single-photon sensitivity and picosecond timing resolution, which is desirable for high-precision three-dimensional (3D) imaging over long distances. Despite important progress, further extending the imaging range presents enormous challenges because only a few echo photons return and are mixed with strong noise. Here, we tackled these challenges by constructing a high-efficiency, low-noise coaxial single-photon lidar system and developing a long-range-tailored computational algorithm that provides high photon efficiency and good noise tolerance. Using this technique, we experimentally demonstrated active single-photon 3D imaging at a distance of up to 45 km in an urban environment, with a low return-signal level of ∼ 1 photon per pixel. Our system is feasible for imaging at a few hundreds of kilometers by refining the setup, and thus represents a step towards low-power and high-resolution lidar over extra-long ranges.

Hydrogarnets Sr3M2(OH)12 (M = Cr, Fe, and Al) were synthesized from mild hydrothermal systems at 240 °C with Sr(OH)2·8H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, and Al(OH)3 as the starting materials. High solubility of the input species and basic concentration in the reaction systems considerably lower crystallization temperatures and enhance the crystallinity of the resulting hydrogarnets. The structural stability and thermal properties of Sr based hydrogarnets were investigated by X-ray diffraction, DTA-TG, infrared, and X-ray photoelectron spectroscopies. With increasing temperature, Sr based hydrogarnets underwent fast dehydration due to the loss of the nearest OH- species of Sr−OH dodecahedra. During the course of decomposition, valence variations of the hydrogarnet framework ions, e.g., Fe and Cr directly determined the decomposition process and phase compositions in final decomposition products. The decomposition product of Sr3Cr2(OH)12 in air was a mixture of SrCrO4 and SrO, but in N2, a mixture of a rhombohedral phase Sr4Cr2O8 with some amorphous phase was observed; in either O2 or N2, Sr3Fe2(OH)12 decomposed to an unknown phase, which was not a perovskite Sr3Fe2O7 - x . Sr3Al2(OH)12 decomposed to a single phase Sr3Al2O6. In Sr−Fe hydrogarnet, two different symmetric octahedra of Fe(OH)6 were revealed by Mossbauer spectroscopy. Mild hydrothermal crystallization and the thermal decomposition behaviors of Sr-based hydrogarnets are discussed.

A search is presented for new particles produced at the LHC in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb−1, collected in 2017–2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb−1, collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.

Measurements of jet substructure describing the composition of quark- and gluon-initiated jets are presented. Proton-proton (pp) collision data at $$ \sqrt{s} $$ s = 13 TeV collected with the CMS detector are used, corresponding to an integrated luminosity of 35.9 fb−1. Generalized angularities are measured that characterize the jet substructure and distinguish quark- and gluon-initiated jets. These observables are sensitive to the distributions of transverse momenta and angular distances within a jet. The analysis is performed using a data sample of dijet events enriched in gluon-initiated jets, and, for the first time, a Z+jet event sample enriched in quark-initiated jets. The observables are measured in bins of jet transverse momentum, and as a function of the jet radius parameter. Each measurement is repeated applying a “soft drop” grooming procedure that removes soft and large angle radiation from the jet. Using these measurements, the ability of various models to describe jet substructure is assessed, showing a clear need for improvements in Monte Carlo generators.