First Measurement of ν_{e} and ν_{µ} Interaction Cross Sections at the LHC with FASER's Emulsion Detector.

The first results of the study of high-energy electron neutrino (ν_{e}) and muon neutrino (ν_{µ}) charged-current interactions in the FASERν emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the FASERν volume was analyzed after exposure to 9.5 fb^{-1} of sqrt[s]=13.6 TeV pp data. Four (eight) ν_{e} (ν_{µ}) interaction candidate events are observed with a statistical significance of 5.2σ (5.7σ). This is the first direct observation of ν_{e} interactions at a particle collider and includes the highest-energy ν_{e} and ν_{µ} ever detected from an artificial source. The interaction cross section per nucleon σ/E_{ν} is measured over an energy range of 560-1740 GeV (520-1760 GeV) for ν_{e} (ν_{µ}) to be (1.2_{-0.7}^{+0.8})×10^{-38} cm^{2} GeV^{-1} [(0.5±0.2)×10^{-38} cm^{2} GeV^{-1}], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges.

Effect of (Poly)electrolytes on the Interfacial Assembly of Poly(ethylene glycol)-Functionalized Gold Nanoparticles.

We report on the effect of interpolymer complexes (IPCs) of poly(acrylic acid) (PAA) with poly(ethylene glycol)-functionalized Au nanoparticles (PEG-AuNPs) as they assemble at the vapor-liquid interface, using surface-sensitive synchrotron X-ray scattering techniques. Depending on the suspension pH, PAA functions both as a weak polyelectrolyte and a hydrogen bond donor, and these two roles affect the interfacial assembly of PEG-AuNPs differently. Above its isoelectric point, we find that PAA leads to the formation of a PEG-AuNP monolayer at the interface with a hexagonal structure. In the presence of high concentration of HCl (i.e., below the isoelectric point), at which PAA forms IPCs with PEG, the hexagonal structure at the interface appears to deteriorate, concurrent with aggregation in the bulk. Thus, while the electrolytic behavior of PAA induces interfacial assembly, the hydrogen bonding behavior, as PAA becomes neutral, favors the formation of 3D assemblies. For comparison, we also report on the formation of PEG-AuNP monolayers (in the absence of PAA) with strong electrolytes such as HCl, H2SO4, and NaOH that lead to a high degree of crystallinity.

Dark matter interpretation of the Fermi-LAT observations toward the outer halo of M31.

An excess γ-ray signal toward the outer halo of M31 has recently been reported. Although other explanations are plausible, the possibility that it arises from dark matter (DM) is valid. In this work we interpret the excess in the framework of DM annihilation, using as our representative case WIMP DM annihilating to bottom quarks, and we perform a detailed study of the systematic uncertainty in the J-factor for the M31 field. We find that the signal favors a DM particle with a mass of ~45-72 GeV. While the mass is well constrained, the systematic uncertainty in the cross section spans 3 orders of magnitude, ranging from ~5 × 10-27-5 × 10-24 cm3 s-1. This high uncertainty is due to two main factors, namely, an uncertainty in the substructure nature and geometry of the DM halos for both M31 and the Milky Way (MW), and correspondingly, an uncertainty in the contribution to the signal from the MW's DM halo along the line of sight. However, under the conditions that the minimum subhalo mass is ≲10-6 M ⊙ and the actual contribution from the MW's DM halo along the line of sight is at least ~30% of its total value, we show that there is a large overlap with the DM interpretations of both the Galactic center (GC) excess and the antiproton excess, while also being compatible with the limits for the MW dwarf spheroidals. More generally, we summarize the results from numerous complementary DM searches in the energy range 10 GeV-300 GeV corresponding to the GC excess and identify a region in parameter space that still remains viable for discovery of the DM particle.