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.

Using x-ray magnetic circular dichroism (XMCD), x-ray absorption spectroscopy (XAS), and energy filtered transmission electron microscopy, we provide evidence for a heterogeneous Co distribution in anatase Co:TiO2 magnetic semiconductor having a low Co concentration (1.4 at. %). Multiplet structure due to Co2+ is observed in XAS spectra, but suppressed due to the coexistence of metallic Co clusters and substitutional Co ions, whereas XMCD spectra resemble metallic Co. The presence of Co2+ can be correlated with earlier observations of impurity band conduction and Kondo behavior, whereas metallic Co clusters contribute to the ferromagnetism and anomalous Hall effect.

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We have studied the electronic structure of Co ions in semiconducting anatase Co:TiO 2 (1.4 at.% Co) with x-ray-absorption spectroscopy. The density of structural defects is varied by (i) the oxygen vacancy concentration depending on the oxygen background pressure during growth, and (ii) the film thickness. The Co L 2,3 -edge spectra, which are characteristic of Co 2+ (3d 7 ) ions, show particularly pronounced ligand-to-metal charge-transfer (CT) satellites for the thickest oxygen-poor films, which also exhibit the highest structural defect density. With charge-transfer multiplet calculations, the CT satellites are modeled by configuration interaction, originating from hybridization between Co 3d-and ligand states. This hybridization adds to the complex interplay between Co heterogeneity, defects, and electronic and magnetic properties in Co:TiO 2 .