Experimental search for neutron–mirror neutron oscillations using storage of ultracold neutrons

The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter. Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n′ with oscillation time much smaller than the neutron lifetime. A dedicated search for vacuum transitions n→n^′$\mathrm{n}\to {\mathrm{n}}^{\prime }$ has to be performed at weak magnetic field, where both states are degenerate. We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions. We obtain a new limit for the oscillation time of n–n′ transitions, τosc(90% C.L.)>414 s${\tau }_{\mathrm{osc}}(90\mathrm{\%}\text{C.L.})>414\text{s}$. The corresponding limit for the mixing energy of the normal and mirror neutron states is δm(90% C.L.)<1.5×¹⁰⁻¹⁸ eV$\delta m(90\mathrm{\%}\text{C.L.})<1.5\times {10}^{\mathrm{-18}}\text{eV}$.     

Trajectory of neutron–neutron–C excited three-body state

The trajectory of the first excited Efimov state is investigated by using a renormalized zero-range three-body model for a system with two bound and one virtual two-body subsystems. The approach is applied to n–n–¹⁸C, where the n–n$n\text{–}n$ virtual energy and the three-body ground state are kept fixed. It is shown that such three-body excited state goes from a bound to a virtual state when the n–¹⁸C binding energy is increased. Results obtained for the n–¹⁹C elastic cross-section at low energies also show dominance of an S-matrix pole corresponding to a bound or virtual Efimov state. It is also presented a brief discussion of these findings in the context of ultracold atom physics with tunable scattering lengths.     

Two-mirror spin–wave neutron interferometer

The characteristics of a spin-wave neutron interferometer comprising two parallel magnetic mirrors located in noncollinear to the magnetizations of the mirrors are investigated. The device can be used to study the properties of the neutron wave packet and measure the time and spatial correlations of material densities in the medium and on the surface. The interferometer’s sensitivity and the observed neutron coherence length are estimated using experimental data. The possible applications of neutron spin-echo spectrometry based on the two-mirror interferometer are discussed.     

Potential of the neutron lloyd’s mirror interferometer for the search for new interactions

We discuss the potential of the neutron Lloyd’s mirror interferometer in a search for new interactions at small scales. We consider three hypothetical interactions that may be tested using the interferometer. The chameleon scalar field proposed to solve the enigma of accelerating expansion of the Universe produces interaction between particles and matter. The axion-like spin-dependent coupling between a neutron and nuclei or/and electrons may result in a P- and T-noninvariant interaction with matter. Hypothetical non-Newtonian gravitational interactions mediates an additional short-range potential between neutrons and bulk matter. These interactions between the neutron and the mirror of a Lloyd-type neutron interferometer cause a phase shift of neutron waves. We estimate the sensitivity and systematic effects of possible experiments.     

More on the dilatonic Einstein–Gauss–Bonnet gravity

Einstein–Gauss–Bonnet gravity coupled to a dynamical dilaton is examined from the viewpoint of Einstein’s equivalence principle. We point out that the usual frame change that applies to the action without curvature correction does not cure the problem of nonminimal couplings by the dynamical nature of a dilaton field. Thus a modification of the Einstein frame is required. It is proposed that the kinetic term of a dilaton should be brought to a canonical form, which completely fixes the additional terms associated with the frame transformation.     

Nano-structured Fabry–Pérot resonators in neutron optics & tunneling of neutron wave-particles

Correlated to the quantum mechanics wave-particle duality, the optical analogy between electromagnetic waves and cold neutrons manifests itself through several interference phenomena particularly the so called Frustrated Total Reflection i.e., the tunneling process in Fabry–Pérot nano-structured cavities. Prominent resonant situations offered by this configuration allow the attainment of numerous fundamental investigations and surface-interface studies as well as to devise new kinds of neutron optics devices. This review contribution reports such possibilities in addition to the recently observed peculiar Goos–Hänchen longitudinal shift of neutron wave-particles which was predicted by Sir Isaac Newton as early as 1730.     

Monte Carlo simulation of thermal neutron flux of americium–beryllium source used in neutron activation analysis

The neutron activation analysis is a method of exclusively elemental analysis. Its implementation of irradiates the sample which can be analyzed by a high neutron flux, this method is widely used in developed countries with nuclear reactors or accelerators of particle. The purpose of this study is to develop a prototype to increase the neutron flux such as americium–beryllium and have the opportunity to produce radioisotopes. Americium–beryllium is a mobile source of neutron activity of 20 curie, and gives a thermal neutron flux of (1.8 ± 0.0007) × 10⁶ n/cm² s when using water as moderator, when using the paraffin, the thermal neutron flux increases to (2.2 ± 0.0008) × 10⁶ n/cm² s, in the case of adding two solid beryllium barriers, the distance between them is 24 cm, parallel and symmetrical about the source, the thermal flux is increased to (2.5 ± 0.0008) × 10⁶ n/cm² s and in the case of multi-source (6 sources), with-out barriers, increases to (1.17 ± 0.0008) × 10⁷ n/cm² s with a rate of increase equal to 4.3 and with the both barriers flux increased to (1.37 ± 0.0008) × 10⁷ n/cm² s.     

Polarization-preserving anisotropic mirror on the basis of metal–dielectric nanocomposite

The model of a polarization-preserving anisotropic mirror is proposed. The mirror is a plane boundary of a metal–dielectric nanocomposite that consists of silver spheroidal nanoparticles dispersed in a transparent matrix. The dependence of reflection spectra on the shape of the nanoparticles is studied. It is shown that in one region of the spectrum, the mirror preserves the sign of polarization in the reflected light.     

The decay of the neutron–rich nucleus 216Bi

The decay of the neutron–rich isotope ²¹⁶Bi, produced by proton–induced spallation at the PS Booster–ISOLDE facility, was investigated by β-γγ, αγ coincidence and spectrum-multiscaling measurements. A new method for reducing isobaric contamination enabled to cover the unknown region “east” of ²⁰⁸Pb for the isobaric chain A=216. The half-life of the β decay of ²¹⁶Bi was found as T_1/2= 135 ± 5 s. Its decay scheme was extended and the possible shell model configurations are proposed. Received: 13 July 1999 / Revised version: 22 September 1999     

Pair-vibrational states in the presence of neutron–proton pairing

Pair vibrations are studied for a Hamiltonian with neutron–neutron, proton–proton and neutron–proton pairing. The spectrum is found to be rich in strongly correlated, low-lying excited states. Changing the ratio of diagonal to off-diagonal pairing matrix elements is found to have a large impact on the excited-state spectrum. The variational configuration interaction (VCI) method, used to calculate the excitation spectrum, is found to be in very good agreement with exact solutions for systems with large degeneracies having equal T=0$T=0$ and T=1$T=1$ pairing strengths.     

Inclusive φ meson production in neutron–carbon interactions at 20–70 GeV

mesons have been reconstructed from their decay to positive and negative kaons, using the data obtained from interaction of neutrons at 20–70 GeV with a carbon target collected by EXCHARM experiment at the Serpukhov accelerator. The analysis relies on the use of reconstructing trajectories and particle identification. From about 45 million events (19600 ± 350) mesons were found. The meson mass is measured to be (1019.4 ± 0.1)MeV/c ²; the meson width is measured to be (4.9 ± 0.3)MeV/c ². The investigation has been performed at the Joint Institute for Nuclear Research at the Laboratory of Super High Energies.     

Cavity-mediated stationary atom–mirror entanglement in the presence of photothermal effects

We study stationary entanglement properties of an optomechanical system containing an atomic ensemble. We focus onto the case of the movable mirror strongly coupled to the cavity field through both radiation pressure and photothermal force. Exploiting a quantum Langevin equation approach we investigate the bipartite entanglement properties of various bipartite subsystems as well as stationary tripartite entanglement of the system. We particularly study robustness of the atom–mirror entanglement against temperature. We show that, even though the photothermal force is a dissipative force, it can significantly improve the cavity mediated atom–mirror entanglement.     

Effects of neutron irradiation on superconducting properties of orthorhombic Y–Ba–Cu oxides

Abstract

We have studied the effects of fast neutron (E>0.1 MeV) irradiation at reactor (～ 360 K) and low (～ 20 K) temperatures on the superconducting properties of polycrystalline orthorhombic YBa₂Cu₃O_7?y . Measurements were made on the superconducting critical temperature T_c , critical current J_c , Meissner effect and magnetic field dependence of J_c . The T_c drops by an irradiation at reactor temperature and J_c increases with increasing fluence. On the other hand with the irradiation at low temperature, T_c rises and J_c increases. Results of observation of Meissner effect and the magnetic field dependence of J_c are consistent with the behavior of T_c and J_c .     

Crust-core properties of neutron stars in the Nambu–Jona-Lasinio model

We adopt the Nambu–Jona-Lasinio(NJL) model to study the crust-core transition properties in neutron stars(NSs). For a given momentum cutoff and symmetry energy of saturation density in the NJL model, decreasing the slope of the symmetry energy gives rise to an increase in the crust-core transition density and transition pressure.Given the slope of the symmetry energy at saturation density, the transition density and corresponding transition pressure increase with increasing symmetry energy. The increasing trend between the fraction of the crustal moment of inertia and the slope of symmetry energy at saturation density indicates that a relatively large momentum cutoff of the NJL model is preferred. For a momentum cutoff of 500 Me V, the fraction of the crustal moment of inertia clearly increases with the slope of symmetry energy at saturation density. Thus, at the required fraction(7%) of the crustal moment of inertia, the NJL model with momentum cutoff of 500 Me V and a large slope of the symmetry energy of saturation density can give the upper limit of the mass of the Vela pulsar to be above 1.40 M_⊙.     

Quantum noise in the mirror–field system: A field theoretic approach

We revisit the quantum noise problem in the mirror–field system by a field-theoretic approach. Here a perfectly reflecting mirror is illuminated by a single-mode coherent state of the massless scalar field. The associated radiation pressure is described by a surface integral of the stress-tensor of the field. The read-out field is measured by a monopole detector, from which the effective distance between the detector and mirror can be obtained. In the slow-motion limit of the mirror, this field-theoretic approach allows to identify various sources of quantum noise that all in all leads to uncertainty of the read-out measurement. In addition to well-known sources from shot noise and radiation pressure fluctuations, a new source of noise is found from field fluctuations modified by the mirror’s displacement. Correlation between different sources of noise can be established in the read-out measurement as the consequence of interference between the incident field and the field reflected off the mirror. In the case of negative correlation, we found that the uncertainty can be lowered than the value predicted by the standard quantum limit. Since the particle-number approach is often used in quantum optics, we compared results obtained by both approaches and examine its validity. We also derive a Langevin equation that describes the stochastic dynamics of the mirror. The underlying fluctuation–dissipation relation is briefly mentioned. Finally we discuss the backreaction induced by the radiation pressure. It will alter the mean displacement of the mirror, but we argue this backreaction can be ignored for a slowly moving mirror.     

Neutrino mixing and masses in a left–right model with mirror fermions

In the framework of a left–right model containing mirror fermions with gauge group SU(3) _C ⊗SU(2) _L ⊗SU(2) _R ⊗U(1) _Y′, we estimate the neutrino masses, which are found to be consistent with their experimental bounds and hierarchy. We evaluate the decay rates of the Lepton Flavor Violation (LFV) processes μ→eγ, τ→μγ and τ→eγ. We obtain upper limits for the flavor-changing branching ratios in agreement with their present experimental bounds. We also estimate the decay rates of heavy Majorana neutrinos in the channels N→W ^± l ^∓, N→Zν _l and N→Hν _l , which are roughly equal for large values of the heavy neutrino mass. Starting from the most general Majorana neutrino mass matrix, the smallness of active neutrino masses turns out from the interplay of the hierarchy of the involved scales and the double application of seesaw mechanism. An appropriate parameterization on the structure of the neutrino mass matrix imposing a symmetric mixing of electron neutrino with muon and tau neutrinos leads to tri-bimaximal mixing matrix for light neutrinos.     

Neutron–antineutron oscillation and baryonic majoron: low scale spontaneous baryon violation

We discuss the possibility that baryon number B is spontaneously broken at low scales, of the order of MeV or even smaller, inducing the neutron–antineutron oscillation at the experimentally accessible level. An associated Goldstone particle–baryonic majoron can have observable effects in neutron to antineutron transitions in nuclei or dense nuclear matter. By extending baryon number to an anomaly-free \(B-L\) symmetry, the baryo-majoron can be identified with the ordinary majoron associated with the spontaneous breaking of lepton number, and it can have interesting implications for neutrinoless \(2\beta \) decay with the majoron emission. We also discuss the hypothesis that baryon number can be spontaneously broken by QCD itself via the six-quark condensates.     

Chemical order in off-stoichiometric Ni–Mn–Ga ferromagnetic shape-memory alloys studied with neutron diffraction

The chemical order of three off-stoichiometry Ni–Mn–Ga compositions has been measured in the austenitic phase using powder and single-crystal neutron diffraction. The compositions studied, 48–52 at.% nickel, having excess manganese and deficient in gallium, are of technical interest due to the observed large room-temperature, magnetic-field-induced strain. It has been determined that compositions with less than 50% nickel have the excess Mn atoms occupying Ni and Ga sites. Compositions enriched in nickel are best fit with Ni atoms in excess of 50% occupying Mn sites while the excess and displaced Mn occupy Ga sites. The saturation magnetic moments calculated from the site occupations determined here and using Ni and Mn moments reported for Ni₂MnGa, agree within 4% with the low-temperature measured moments.     

Direct time domain observation of exciton–polariton oscillation in a semiconductor microcavity

We measured temporal evolution of the coherent emission from a semiconductor microcavity by an ac-balanced homodyne detector with high sensitivity and wide dynamic range. The experimental results can be well explained by the coupled exciton–photon model.