Results are presented from the first underground data run of ZEPLIN-II, a 31
kg two-phase xenon detector developed to observe nuclear recoils from hypothetical weakly interacting massive dark matter ...particles. Discrimination between nuclear recoils and background electron recoils is afforded by recording both the scintillation and ionisation signals generated within the liquid xenon, with the ratio of these signals being different for the two classes of event. This ratio is calibrated for different incident species using an AmBe neutron source and
60Co γ-ray sources. From our first 31 live days of running ZEPLIN-II, the total exposure following the application of fiducial and stability cuts was 225
kg
×
days. A background population of radon progeny events was observed in this run, arising from radon emission in the gas purification getters, due to radon daughter ion decays on the surfaces of the walls of the chamber. An acceptance window, defined by the neutron calibration data, of 50% nuclear recoil acceptance between 5
keV
ee and 20
keV
ee, had an observed count of 29 events, with a summed expectation of 28.6
±
4.3 γ-ray and radon progeny induced background events. These figures provide a 90% c.l. upper limit to the number of nuclear recoils of 10.4 events in this acceptance window, which converts to a WIMP–nucleon spin-independent cross-section with a minimum of 6.6
×
10
−7
pb following the inclusion of an energy-dependent, calibrated, efficiency. A second run is currently underway in which the radon progeny will be eliminated, thereby removing the background population, with a projected sensitivity of 2
×
10
−7
pb for similar exposures as the first run.
A new vacuum-insulated tandem accelerator capable of producing a 5-mA proton beam with energy up to 2MeV was used to produce a mono-energetic beam of 9.17-MeV gamma rays from the resonant production ...reaction, 13C(p,γ)14N, at 1.76MeV. A graphite target enriched with 13C capable of withstanding the proton beam power was designed and fabricated. The 9.17-MeV gamma rays were subsequently resonantly absorbed in 14N via the inverse reaction, 14N(γ,p)13C. The data acquisition system to measure the resonance absorption in nitrogen includes a BGO detector and a goniometer and collimator assembly that rotate around the axis produced by the intersection of the proton beam and the production target. The accuracy of rotation of the detector around the target is approximately 0.1°. The results of the resonance gamma ray absorption measurements are presented to demonstrate the feasibility of the method to sensitively and selectively detect high concentrations of nitrogen, comparable to those found in most explosives.
We present results from a search for solar axions with the COSINE-100 experiment. We find no evidence of solar axion events from a data-set of 6,303.9 kg · days exposure and set a 90% confidence ...level upper limit on the axion-electron coupling, gae, of 1.70 ×10−11 for an axion mass less than 1 keV/c2. This limit excludes QCD axions heavier than 0.59 eV/c2 in the DFSZ model and 168.1 eV/c2 in the KSVZ model.
We studied the kink-antikink collision process for the "double sine-Gordon" (DSG) equation in 1+1 dimensions at different values of the potential parameter R>0. For small values of R we discuss the ...problem of resonance frequencies. We give qualitative explanation of the frequency shift in comparison with the frequency of the discrete level in the potential well of isolated kink. We show that in this region of the parameter R the effective long-range interaction between kink and antikink takes place.
High-entropy Alloys (HEAs) are considered prospective materials demonstrating the new approach of alloy design creating new compositions for harsh conditions. However, searching for alloy chemical ...composition providing the best material properties is a costly process. Additive manufacturing (AM) can be an effective technique for adjusting the alloy composition by using several initial materials. The powder bed fusion (PBF) AM process allows the printing of solid parts using powder blends. In the present study, the CrFeCoNi(Al,Ti) HEAs were printed by the PBF technique using the blends of three powders. The structural and phase investigations revealed the chemical inhomogeneity in the materials that led to the new phase formations affecting the mechanical characteristics. The high-temperature annealing at 1200 °C can be considered a post-treatment process for the printed alloys as a homogenization process while the annealing at a lower temperature of 800 °C initiates the decomposition of the initially formed f.c.c. phase.
A computer-aided two-photon scanning microscope Semin, S. V.; Kudryavtsev, A. V.; Mishina, E. D.
Instruments and experimental techniques (New York),
2012/1, Letnik:
55, Številka:
1
Journal Article
Recenzirano
A computer-aided digital microscope for studying microstructures at wavelengths of the second optical harmonic and two-photon luminescence is designed. In contrast to commercial instruments, the ...microscope is intended to study the image dependence on the angle of incidence, azimuth, and angle of the radiation receipt, as well as the polarization characteristics in organic and inorganic structures. As examples, results of studying nonlinearly optical properties of peptide tubes and microstructures based on zinc oxide are given.
We perform a complete calculation of charge symmetry breaking effects for the reaction pn→dπ0 at leading order in chiral perturbation theory. A new leading-order operator is included. From our ...analysis we extract δmNstr, the strong contribution to the neutron–proton mass difference. The value obtained, δmNstr=(1.5±0.8 (exp.)±0.5 (th.)) MeV, is consistent with the result based on the Cottingham sum rule. This agreement provides a non-trivial test of our current understanding of the chiral structure of QCD.
We present the results from combining machine learning with the profile likelihood fit procedure, using data from the Large Underground Xenon (LUX) dark matter experiment. This approach demonstrates ...reduction in computation time by a factor of 30 when compared with the previous approach, without loss of performance on real data. We establish its flexibility to capture non-linear correlations between variables (such as smearing in light and charge signals due to position variation) by achieving equal performance using pulse areas with and without position-corrections applied. Its efficiency and scalability furthermore enables searching for dark matter using additional variables without significant computational burden. We demonstrate this by including a light signal pulse shape variable alongside more traditional inputs such as light and charge signal strengths. Furthermore, this technique can be exploited by future dark matter experiments to make use of additional information, reduce computational resources needed for signal searches and simulations, and make inclusion of physical nuisance parameters in fits tractable.
PDF
