Surface-enhanced Raman scattering (SERS)-active plasmonic nanomaterials have become a promising agent for molecular imaging and multiplex detection. To produce strong SERS intensity while retaining the non-aggregated state and biocompatibility needed for bioapplications, we integrated near infrared (NIR) responsive plasmonic gold nanostars with resonant dyes for resonant SERS (SERRS). The SERRS on nanostars was several orders of magnitude greater than signals from SERRS on nanospheres and non-resonant SERS on nanostars. For the first time, we demonstrated quantitative multiplex detection using 4 unique nanostar SERRS probes in both in vitro solutions and ex vivo tissue samples under NIR excitation. With further optimization, in vivo tracking of multiple SERRS probes is possible.

A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in pp collisions at $$ \sqrt{s} $$ s = 13 TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb−1, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of c- or b-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass.

Plasmonic gold nanostars offer a new platform for Surface-Enhanced Raman Scattering (SERS). However, due to the presence of organic surfactant on the nanoparticles, SERS characterization and application of nanostar ensembles in solution have been challenging. Here we applied our newly developed surfactant-free nanostars for SERS characterization and application. The SERS enhancement factors (EF) of silver spheres, gold spheres and nanostars of similar sizes and concentration were compared. Under 785 nm excitation, nanostars and silver spheres have similar EF, and both are much stronger than gold spheres. Having plasmon matching the incident energy and multiple “hot spots” on the branches bring forth strong SERS response without the need to aggregate. Intracellular detection of silica-coated SERS-encoded nanostars was also demonstrated in breast cancer cells. The non-aggregated field enhancement makes the gold nanostar ensemble a promising agent for SERS bioapplications.

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

A search for weakly interacting massive darkmatter particles produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and missing 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 interpreted 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 darkmatter 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. IntroductionAstrophysical observations have provided compelling evidence for the existence of a non-baryonic dark component of the universe: dark matter (DM) [1,2]. The currently most accurate, although somewhat indirect, determination of DM abundance comes from global fits of cosmological parameters to a variety of observations [3,4], while the nature of DM remains largely unknown. One of the candidates for a DM particle is a weakly interacting massive particle (WIMP) [5]. e-mail: atlas.publications@cern.ch At the large hadron collider (LHC), one can search for WIMP DM (χ ) pair production in pp collisions. WIMP DM would not be detected and its production leads to signatures with missing transverse momentum. Searches for the production of DM in association with Standard Model (SM) particles have been performed at the LHC [6][7][8][9][10][11][12].Recently proposed simplified benchmark models for DM production assume the existence of a mediator particle which couples both to the SM and to the dark sector [13][14][15]. The searches presented in this paper focus on the case of a fermionic DM particle produced through the exchange of a spin-0 mediator, which can be either a colour-neutral scalar or pseudoscalar particle (denoted by φ or a, respectively) or a colour-charged scalar mediator (φ b ). The couplings of the mediator to the SM fermions are severely restricted by precision flavour measurements. An ansatz that automatically relaxes these constraints is Minimal Flavour Violation [16]. This assumption implies that the interaction between any new neutral spin-0 state and SM matter is proportional to the fermion masses via Yukawa-type couplings.1 It follows that colour-neutral mediators would be sizeably produced through lo...