The violation of baryon number, B , is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the Universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR program is a proposed two-stage experiment at the European Spallation Source to search for baryon number violation. The program will include high-sensitivity searches for processes that violate baryon number by one or two units: free neutron–antineutron oscillation ( n → n ̄ ) via mixing, neutron–antineutron oscillation via regeneration from a sterile neutron state ( n → [ n ′ , n ̄ ′ ] → n ̄ ), and neutron disappearance (n → n′); the effective Δ B = 0 process of neutron regeneration ( n → [ n ′ , n ̄ ′ ] → n ) is also possible. The program can be used to discover and characterize mixing in the neutron, antineutron and sterile neutron sectors. The experiment addresses topical open questions such as the origins of baryogenesis and the nature of dark matter, and is sensitive to scales of new physics substantially in excess of those available at colliders. A goal of the program is to open a discovery window to neutron conversion probabilities (sensitivities) by up to three orders of magnitude compared with previous searches. The opportunity to make such a leap in sensitivity tests should not be squandered. The experiment pulls together a diverse international team of physicists from the particle (collider and low energy) and nuclear physics communities, while also including specialists in neutronics and magnetics.

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechanism for superconductivity. For iron pnictide superconductors, the s ± -pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies (E 2 ) below T c . On the other hand, the s ++ -pairing symmetry expects a broad spin excitation enhancement at an energy above 2 below T c . Although the resonance has been observed in iron pnictide superconductors at an energy below 2 consistent with the s ± -pairing symmetry, the mode has also been interpreted as arising from the s ++ -pairing symmetry with E 2 due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at E = 7 meV in SC NaFe 0.935 Co 0.045 As (T c = 18 K). On warming towards T c , the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitation spectra within the s ± and s ++ -pairing symmetries, we conclude that the ground-state resonance in NaFe 0.935 Co 0.045 As is only consistent with the s ± pairing, and is inconsistent with the s ++ -pairing symmetry.

Current mainstream spectroscopic scintillators for the detection of high-energy radiation are based on inorganic crystals and ceramics, which are difficult to scale up. Efforts have been made to synthesize plastic nanocomposite scintillators, though the resulting light yield is rather low, leading to low photopeak intensity and poor energy resolution. Here, a scintillating liquid containing HfO 2 nanoparticles for increasing sensitivity to high-energy photons is demonstrated, with the addition of 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as a primary dye and 1,4-bis(5phenyloxazol-2-yl) benzene (POPOP) as a secondary dye. Naphthalene is used as a cosolvent for toluene to dissolve these functional components. The liquid scintillator retains a high transparency in the emission wavelength range, achieving a transmittance of up to 80% at nanoparticle loadings as high as 50 wt %. The use of the naphthalene cosolvent increases the light yield by 40%. The 137 Cs γ photopeak is measured from the liquid scintillator containing 20 wt % HfO 2 nanoparticles, with a deconvoluted photopeak energy resolution of 4.8%, which is better than that obtained from the conventional NaI(Tl) crystal scintillator.

Pulse shape discrimination (PSD)‐capable plastic scintillator is in demand for the detection of high‐energy neutrons in the presence of gamma radiation background. Conventional PSD plastics are based on delayed fluorescent dye via triplet–triplet annihilation of a fluorescent dye additive, which is inefficient to harvest the energy of triplet excitons. In recent years, thermally activated delayed fluorescence (TADF) emitters have gained substantial success in organic light‐emitting diodes due to their efficient utilization of the energy of triplet excitons and thereby achieving theoretical unity internal quantum efficiencies. Herein, a highly efficient TADF dye 9‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)‐2‐methylphenyl)‐3,6‐dioctyl‐9H‐carbazole is reported for the PSD application. This TADF dye may be loaded up to 30 wt% in polyvinyltoluene matrix and still retains high optical transparency. High scintillation light yield and PSD figures of merit are obtained from the TADF plastic. With the introduction of a secondary dye to further increase the utilization efficiency of the excitation energy, the light yield is increased to 6948 photons MeV−1. The measured alpha/gamma PSD figure of merit is 1.12 at the energy threshold of 100 keVee and neutron/gamma PSD figure of merit is 1.32 at the threshold of 1000 keVee.

The in-plane longitudinal and Hall resistivities, ρxx and ρxy, of superconducting NaFe1-xCoxAs (NFCA) single crystals with x = 0.022 and 0.0205 in the mixed state and the normal state were measured to study the electrical transport properties in nearly optimum-doping iron-based superconductors. The resistivities under magnetic fields show thermally activated behavior and a power law magnetic field dependence of activation energy has been obtained. Due to the weak flux pinning, there is no sign reversal of Hall resistivities observed for NFCA with either x = 0.022 or 0.0205. The correlation between longitudinal and Hall resistivities shows that the scaling behavior of |ρxy| ∝ (ρxx)(β) with the exponent β ≈ 2.0 is in agreement with theoretical predictions for weak-pinning superconductors. Anisotropic upper critical fields and coherence lengths with an anisotropy ratio of γ ≈ 1.63 have been deduced. Furthermore, the normal-state transport properties show that the anomalies of the linear-T resistivity, the T(2)-dependent cotangent of the Hall angle, the linear-T-like Hall number, and the magnetoresistance, which can be scaled by the modified Kohler rule, are analogous to those observed on optimally doped high-Tc superconducting cuprates and other pnictides. The longitudinal resistivity can be understood within a widely accepted scenario of the spin density-wave quantum critical point, while the transverse resistivity requires some further explanation. It is suggested that all the transport anomalies should be simultaneously taken into account when developing theory.