The reactor antineutrino anomaly might be explained by the oscillation of reactor antineutrinos toward a sterile neutrino of eV mass. In order to explore this hypothesis, the STEREO experiment ...measures the antineutrino energy spectrum in six different detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this Letter, results from 66 days of reactor turned on and 138 days of reactor turned off are reported. A novel method to extract the antineutrino rates has been developed based on the distribution of the pulse shape discrimination parameter. The test of a new oscillation toward a sterile neutrino is performed by comparing ratios of cells, independent of absolute normalization and of the prediction of the reactor spectrum. The results are found to be compatible with the null oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5% C.L.
5
μm thick CrN–Ag composite layers, containing 22
at.% Ag solid lubricant, were deposited by reactive magnetron co-sputtering on 440C stainless-steel substrates at
T
s
=
300, 400, 500, and 600
°C. ...Vacuum annealing experiments at
T
a
=
425, 525, and 625
°C show that Ag diffuses to the coating surface to form lubricious surface aggregates and that the rate for Ag lubricant transport increases with
T
a
>
T
s, as determined by quantitative electron microscopy surface analyses. However, the Ag remains in the CrN matrix for
T
a
<
T
s. This is attributed to an increasing Ag aggregate size within the composite with increasing
T
s, leading to a decrease in the chemical potential and, in turn, negligible diffusion until
T
a exceeds
T
s. The tribological response during ball-on-disk sliding in ambient air against 6-mm-alumina balls was found to depend strongly on both
T
s and the testing temperature
T
t
=
450, 550, and 650
°C. The key parameter that determines lubricant transport and, in turn, tribological properties is the temperature difference Δ
T
=
T
t
−
T
s. For Δ
T
<
0, the lubricious Ag within the CrN matrix causes a moderate (25–35%) reduction in the friction coefficient from
μ
=
0.41–0.51 for pure CrN to
μ
=
0.31–0.34 for the composite. In contrast, at Δ
T
>
0, the Ag diffuses to the surface, partially transfers to the counterface, and forms a lubricious interface layer, reducing the friction by up to 60% to
μ
=
0.16–0.24. However, continuous wear at Δ
T
>
0 causes Ag depletion which results in an increasing friction and wear, and ultimately mechanical failure of the coating. The lubricant transport rate and, in turn, the lifetime before the Ag is depleted depend both strongly on Δ
T, and can therefore be optimized for a given application.
The modeling of neutrino-nucleus interactions constitutes a challenging source of systematic uncertainty for the extraction of precise values of neutrino oscillation parameters in long-baseline ...accelerator neutrino experiments. To improve such modeling and minimize the corresponding uncertainties, a new generation of detectors is being developed, which aim to measure the complete final state of particles resulting from neutrino interactions. In order to fully benefit from the improved detector capabilities, precise simulations of the nuclear effects on the final-state nucleons are needed. This article presents the study of the in-medium propagation of knocked-out protons, i.e., final-state interactions (FSI), comparing the NuWro and INCL cascade models. The INCL model is used here for the first time to predict exclusive final states in measured neutrino interaction cross sections. This study of INCL in the framework of neutrino interactions features various novelties, including the production of nuclear clusters (e.g., deuterons, α particles) in the final state. The paper includes a complete characterization of the final state after FSI, comparisons to available measurements of single transverse variables, and an assessment of the observability of nuclear clusters.
Ion-exchange is a popular method to strengthen alkali-containing glasses. However, the experimentally observed residual compressive stress profiles often deviate from the theoretical profiles: a ...subsurface compression maximum is often observed, while monotonically decreasing stress with depth is expected. It is suggested here that this discrepancy can be accounted for by considering a surface stress relaxation process that takes place at a faster rate than bulk stress relaxation in the presence of water. This suggestion is based upon experimental data indicating the presence of water impurity in the molten salt used for ion-exchange strengthening of glasses. Recent work characterizing surface stress relaxation in oxide glass fibers as a diffusion controlled process aided by molecular water diffusion was applied to better explain the development of a subsurface compressive maximum within an accelerated timeframe. By combining the new surface stress relaxation diffusion mechanism with the well-established ion-exchange mechanism, a mathematical model predicting a subsurface maximum stress is developed with a good agreement to published data.
•A surface relaxation mechanism is shown to cause subsurface compressive stress peak.•Hastened surface relaxation is due to trace water impurity in the molten salt.•Analytical models developed to predict ion-exchanged glass stress-depth profiles.
The most challenging and impactful uncertainties that future accelerator-based measurements of neutrino oscillations must overcome stem from our limited ability to model few-GeV neutrino-nucleus ...interactions. In particular, it is crucial to better understand the nuclear effects which can alter the final state topology and kinematics of neutrino interactions, inducing possible biases in neutrino energy reconstruction. The upgraded ND280 near detector of the T2K experiment will directly confront neutrino interaction uncertainties using a new suite of detectors with full polar angle acceptance, improved spatial resolutions, neutron detection capabilities and reduced tracking thresholds. In this manuscript we explore the physics sensitivity that can be expected from the upgraded detector, specifically focusing on the additional sensitivity to nuclear effects and how they can be constrained with future measurements of kinematic variables constructed using both outgoing lepton and nucleon kinematics.
Anomalies in past neutrino measurements have led to the discovery that these particles have non-zero mass and oscillate between their three flavours when they propagate. In the 2010s, similar ...anomalies observed in the antineutrino spectra emitted by nuclear reactors have triggered the hypothesis of the existence of a supplementary neutrino state that would be sterile, that is, not interacting by means of the weak interaction1. The STEREO experiment2-6 was designed to investigate this conjecture, which would potentially extend the standard model of particle physics. Here we present an analysis of the full set of data generated by STEREO, confirming observed anomalies while rejecting the hypothesis of a light sterile neutrino. Installed at the Institut Laue-Langevin (ILL) research reactor, STEREO accurately measures the antineutrino energy spectrum associated to the fission of 235U. The segmentation of the detector and its very short distance to the compact core are crucial properties of STEREO for our analysis. The measured antineutrino energy spectrum suggests that anomalies originate from biases in the nuclear experimental data used for the predictions7,8. Our result supports the neutrino content of the standard model and establishes a new reference for the 235U antineutrino energy spectrum. We anticipate that this result will allow progress towards finer tests of the fundamental properties of neutrinos but also to benchmark models and nuclear data of interest for reactor physics9,10 and for observations of astrophysical or geoneutrinos11,12.
CrN–Ag composite coatings, 2 and 5
μm thick and containing 22
at.% Ag solid lubricant, were grown on Si(001) and 440C stainless steel substrates by reactive co-sputtering at T
s
=
500
°C, and were ...covered with 200
nm thick pure CrN diffusion barrier cap layers. Annealing experiments at T
a
=
625
°C, followed by quantitative scanning electron microscopy, energy dispersive x-ray spectroscopy, and Auger depth profile analyses indicate considerable Ag transport to the top surface for a barrier layer deposited at a substrate floating potential of −30
V, but negligible Ag diffusion when deposited with a substrate bias potential of −150
V. This is attributed to ion-irradiation induced densification which makes the cap layer an effective diffusion barrier. High temperature tribological sliding tests of this coating system against alumina balls at T
t
=
550
°C indicate an initial friction coefficient μ
=
0.43
±
0.04 which decreases monotonically to 0.23
±
0.03. This is attributed to the development of wear mediated openings in the barrier layer which allow Ag lubricant to diffuse to the sliding top surface. In contrast, pure CrN exhibits a constant μ
=
0.41
±
0.02 while CrN–Ag composite coatings without cap layer show a low transient μ
=
0.16
±
0.03, attributed to Ag transport to the surface, that however increases to μ
=
0.39
±
0.04 after ~
6000
cycles as the Ag reservoir in the coating is depleted. That is, the dense CrN cap layer reduces the Ag lubricant flow rate and therefore prolongs the time when the coating provides effective lubrication. This results in a cumulative wear rate over 10,000 cycles of 3.1
×
10
−6
mm
3/Nm, which is 3.3
×
lower than without diffusion barrier layer.
Different extensions of the standard model of particle physics, such as braneworld or mirror matter models, predict the existence of a neutron sterile state, possibly as a dark matter candidate. This ...Letter reports a new experimental constraint on the probability p for neutron conversion into a hidden neutron, set by the STEREO experiment at the high flux reactor of the Institut Laue-Langevin. The limit is p<3.1×10^{-11} at 95% C.L. improving the previous limit by a factor of 13. This result demonstrates that short-baseline neutrino experiments can be used as competitive passing-through-walls neutron experiments to search for hidden neutrons.
Pristine silica glass fiber is well known to become mechanically weaker when heat-treated in the presence of water vapor. However, the same fiber was found to become stronger if heat-treated while ...held under a sub-critical tensile stress at a temperature far below the glass transition temperature. The added strength of the stress-treated fiber was nearly equal to the applied tensile stress. This added strength was attributed to the formation of a compressive stress layer on the surface of the glass, created by a surface stress relaxation process that occurred while being held under the tensile stress. The presence of the surface compressive stress was confirmed by observing the bending of the fiber when 1) a tensile-stressed fiber was sliced and 2) a bending-stressed fiber was released from the stress. In the present paper we demonstrate that even though heat-treatment of a silica glass fiber in water vapor weakens the glass, a tensile stress application during the heat-treatment can increase the strength of silica glass fibers. Silica glass fibers with estimated strengths of ~7–8GPa were produced, exceeding that of other fibers previously reported to have a maximum strength of ~5.5GPa at room temperature in air. This new glass strengthening method does not require glass to be of a minimum thickness, as in tempering, or a glass containing alkali ions, as in ion-exchange.
•Silica glass fiber becomes stronger when heated while subjected to a tensile stress.•The fiber subjected to tensile stress acquires a surface residual compressive stress.•The residual stress is produced by surface stress relaxation promoted by water.
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