Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Deterministic Single-Photon and Polarization-Correlated Photon Pair Generations From a Single InAlAs Quantum Dot

Photon emission with nonclassical photon statistics is discussed with a single InAlAs quantum dot. The deterministic single-photon generation in which the emitted photon wavelength matches well to the highly sensitive wavelength region of highly efficient, low-noise Si-single-photon detectors and also to an atmospheric transmission window is demonstrated. Competing transition processes between neutral and charged exciton species originating from an exclusive formation in the same single quantum dot are clarified. It was found that suppressing the charged exciton formation is possible by a quasi-resonant excitation for a deterministic monochromatic single-photon generation. Polarization-dependent photoluminescence spectroscopy clearly indicates the preservation of photon polarizations between photons emitted by biexciton/exciton recombinations. Furthermore, the deterministic polarization-correlated photon pair generation with biexciton-exciton cascaded transition occurring in a single quantum dot is directly confirmed by the polarized second-order photon correlation measurements. This indicates a longer polarization flip time than the exciton lifetime, which is an essential requirement for the deterministic Einstein-Podolsky-Rosen photon pair generation under the present biexciton-exciton cascaded transition scheme