Ultrafast single photon emitting quantum photonic structures based on a nano-obelisk

A key issue in a single photon source is fast and efficient generation of a single photon flux with high light extraction efficiency. Significant progress toward high-efficiency single photon sources has been demonstrated by semiconductor quantum dots, especially using narrow bandgap materials. Meanwhile, there are many obstacles, which restrict the use of wide bandgap semiconductor quantum dots as practical single photon sources in ultraviolet-visible region, despite offering free space communication and miniaturized quantum information circuits. Here we demonstrate a single InGaN quantum dot embedded in an obelisk-shaped GaN nanostructure. The nano-obelisk plays an important role in eliminating dislocations, increasing light extraction, and minimizing a built-in electric field. Based on the nano-obelisks, we observed nonconventional narrow quantum dot emission and positive biexciton binding energy, which are signatures of negligible built-in field in single InGaN quantum dots. This results in efficient and ultrafast single photon generation in the violet color region

Inclusive B-meson flavour-tagging algorithm at LHCb

A new algorithm is developed to identify the flavour of neutral B mesons at production in pp collisions by utilising all tracks from the hadronisation process. The algorithm is calibrated separately for B0 and Bs0 mesons using B0 → J/ψK+π− and Bs0→Ds−π+ decays from pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. This new algorithm improves the tagging power by 35% for B0 mesons and 20% for Bs0 mesons when compared to the combined performance of the existing LHCb flavour-tagging algorithms

Improved measurement of η/η′ mixing in B(s)0 → J/ψη(′) decays

Branching fraction ratios between the decays B(s)0→J/ψη(′) are measured using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The measured ratios of these branching fractions areB(B0→J/ψη′BB0→J/ψη)=0.48±0.06±0.02±0.01, B(Bs0→J/ψη′)B(Bs0→J/ψη)=0.80±0.02±0.02±0.01, where the uncertainties are statistical, systematic and related to the precision of the η(′) branching fractions, respectively. They are used to constrain the η/η′ mixing angle, ϕP, and to probe the presence of a possible glueball component in the η′ meson, described by the gluonic mixing angle ϕG. The obtained results are ϕP=41.6−1.2+1.0∘, ϕG=28.1−4.0+3.9∘, where the uncertainties are statistically dominated. While the value of ϕP is compatible with existing experimental determinations and theoretical calculations, the angle ϕG differs from zero by more than four standard deviations, which points to a substantial glueball component in the η′ meson and/or unexpectedly large contributions from gluon-mediated processes in these decays. The absolute branching fractions are also measured relative to that of the well-established Bs0→J/ψϕ decay, which serves as the normalisation channel. These results supersede the previous LHCb measurements and are the most precise to date

Updated measurement of CP violation and polarisation in Bs0 → J/ψK¯∗ (892)0 decays

A time-integrated angular analysis of the decay Bs0→J/ψK¯∗(892)0, with J/ψ → μ+μ− and K¯∗(892)0→K−π+, is presented. The analysis employs a sample of proton-proton collision data collected by the LHCb experiment during 2015–2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb−1. A simultaneous maximum-likelihood fit is performed to the angular distributions in bins of the K−π+ mass. This fit yields measurements of the CP-averaged polarisation fractions and CP asymmetries for the P-wave component of the K−π+ system. The longitudinal and parallel polarisation fractions are determined to be f0 = 0.534 ± 0.012 ± 0.009 and f|| = 0.211 ± 0.014 ± 0.005, respectively, where the first uncertainty is statistical and the second is systematic. The CP asymmetries are measured with 3–7% precision and are found to be consistent with zero. These measurements, along with an updated determination of the branching fraction relative to the B0 → J/ψK*0 decay, are combined with previous LHCb results, providing the most precise values for these observables to date