More about neutron–mirror neutron oscillation

It was pointed out recently that oscillation of the neutron n into a mirror neutron n′, a sterile twin of the neutron with exactly the same mass, could be a very fast process with baryon number violation, even faster than the neutron decay itself. This process is sensitive to magnetic fields and it could be observed by comparing the neutron loss rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of the n−n′ oscillation in the case when a mirror magnetic field B′ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field B, depending on its strength and on its orientation with respect to B′. The recent experimental data, under this hypothesis, still allow for an n−n′ oscillation time of order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation of the magnetic field. If these hints will be confirmed in future experiments, this would point to the presence of a mirror magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of other origin that makes a difference between the neutron and mirror neutron states.     

Neutron-mirror-neutron oscillations: how fast might they be?

We discuss the phenomenological implications of the neutron (n) oscillation into the mirror neutron (n'), a hypothetical particle exactly degenerate in mass with the neutron but sterile to normal matter. We show that the present experimental data allow a maximal n-n' oscillation in vacuum with a characteristic time tau much shorter than the neutron lifetime, in fact as small as 1 sec. This phenomenon may manifest in neutron disappearance and regeneration experiments perfectly accessible to present experimental capabilities and may also have interesting astrophysical consequences, in particular, for the propagation of ultra high energy cosmic rays.     

Magnetic anomaly in UCN trapping: signal for neutron oscillations to parallel world?

Present experiments do not exclude that the neutron n oscillates, with an appreciable probability, into its invisible degenerate twin from a parallel world, the so-called mirror neutron n′. These oscillations were searched experimentally by monitoring the neutron losses in ultra-cold neutron traps, where they can be revealed by the magnetic field dependence of n–n′ transition probability. In this work we reanalyze the experimental data acquired by the group of A.P. Serebrov at Institute Laue–Langevin, and find a dependence at more than 5σ away from the null hypothesis. This anomaly can be interpreted as oscillation of neutrons to mirror neutrons with a timescale of few seconds, in the presence of a mirror magnetic field order 0.1 G at the Earth. This result, if confirmed by future experiments, will have deepest consequences for fundamental particle physics, astrophysics and cosmology.     

Monte Carlo方法计算快中子在样品中多次散射和通量衰减修正因子

本文叙述计算快中子在样品中自吸收通量衰减因子以及(n,γ)和(n,n')反应多次散射修正因子的Monte Carlo方法数学处理过程。     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypemuclear physics.In order to know the influences introduced by a single Lambda hyperon,we study the binding energy difference of mirror hypemuclear pair with mass A = 16,18,28,40,and 42 using a time-odd triaxial relativistic mean field theory.Effects as the spin-orbit interaction,the time-odd component of vector fields,the core polarization,the proton-neutron mass difference,and the center-of-mass energy correction are self-consistently considered.Compared to the reported results of ordinary nuclei,the binding energy difference of mirror hypernuclei shows trivial change.With core polarization modified by an impurity hyperon,the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

Balance of neutrons during their transport through magnetic noncollinear and noncoplanar layered systems

The violation of the detailed balance principle (DBP) for polarized neutrons during their mirror reflection and transport through a two-layered noncollinear magnetic structure in a magnetic field (noncoplanar system), and without it (noncollinear system), is revealed. Moreover, the existence of left-right non-polarized neutron transmission asymmetry for a noncoplanar layered system is uncovered.     

Evidence for heating of neutron stars by magnetic-field decay

We show the existence of a strong trend between neutron star (NS) surface temperature and the dipolar component of the magnetic field extending through three orders of field magnitude, a range that includes magnetars, radio-quiet isolated neutron stars, and many ordinary radio pulsars. We suggest that this trend can be explained by the decay of currents in the crust over a time scale of approximately 10(6) yr. We estimate the minimum temperature that a NS with a given magnetic field can reach in this interpretation.     

Temperature‐Anisotropy Driven Mirror Waves in Space Plasma

In this paper an analysis of the excitation conditions of mirror waves is done, which propagate parallel to an external magnetic field. There are found analytical expressions for the dispersion relations of the waves in case of different plasma conditions. These relations may be used in future to develop the nonlinear theory of mirror waves. In comparison with former analytical works, in the study the influence of the magnetic field and finite temperatures of the ions parallel to the magnetic field are taken into account. Application is done for the earth's magnetosheath.     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypernuclear physics. In order to know the influences introduced by a single Lambda hyperon, we study the binding energy difference of mirror hypernuclear pair with mass A=16, 18, 28, 40, and 42 using a time-odd triaxial relativistic mean field theory. Effects as the spin-orbit interaction, the time-odd component of vector fields, the core polarization, the proton-neutron mass difference, and the center-of-mass energy correction are self-consistently considered. Compared to the reported results of ordinary nuclei, the binding energy difference of mirror hypernuclei shows trivial change. With core polarization modified by an impurity hyperon, the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

Magnetic structures and neutron polarimetry

In a thermal neutron scattering experiment, Spherical Neutron Polarimetry (SNP) requires that the incident and the final neutron polarization vectors be measured independently. The method exploits the maximum information one can get from magnetic neutron scattering. Recently, it has been used quite successfully in the study of antiferromagnetic structures and their domain populations. The challenging measurement is now straightforward with our neutron polarimeter CRYOPAD as long as the sample chamber does not contain any magnetic field. Polarimetry on magnetized samples remains the domain of the classical Uniax ial Polarization Analysis (UPA) which measures only the longitudinal component of polarization in an applied field.     

Experimente mit dem neutronenspinecho mit langwelligen neutronen aus einem polarisierenden neutronenleiter

We describe an inexpensive method to obtain a highly polarized neutron beam of slow neutrons (λ = 1 – 15 Å) [1]. The high necessary field to saturate the applied soft magnetic material in the surface acting as a polarizing mirror indicates a behaviour of the magnetization in the surface different from that in the bulk material [2]. We also describe the realization of an apparatus proposed by F. Mezei [3], the behaviour of the polarized neutrons in this apparatus, and its use to get a spin echo with a neutron spectrum containing 3 – 9 Å wavelength neutrons. This spin echo is not destroyed by transmission through a nickel sheet, only the number of precessions is increased which appear in a displacement of the echo. This displacement can be used to measure the saturation magnetization of this sheet.     

On the neutronization radius of magnetic neutron stars: The field and temperature dependences of the chemical potential and minimum number density of a degenerate magnetized electron gas

The temperature and field dependences of the chemical potential and the field dependence of the Fermi energy for a degenerate relativistic electron gas in a magnetic field have been analyzed by numerical and analytical methods. An analytical expression has been derived for the dependence of the minimum electron number density and the corresponding neutronization radius on the magnetic field strength in a collapsing star upon its subsequent transformation into a neutron one. We believe that a similar relation also holds for the equilibrium neutron star radius. Our results refine the conclusions reached previously [1] in the case of a nonzero temperature and the influence of the star??s proton component on the neutronization process as well as confirm and generalize them in terms of a significant (by an order of magnitude or severalfold) decrease in the equilibrium radius of a neutron star in a superstrong (10¹⁴?C10¹⁷ G) magnetic field compared to the case where there is no such field. We point out that there may exist a separate class of stellar objects??very small magnetar neutron stars that we propose to name ??minimagnetars??. We hypothesize that they can be the final evolutionary stage of stars before their collapse into a black hole.     

Neutrinoless neutron decay feasibility

Within nonrelativistic quantum mechanics, it is shown that there is a virtual level in the energy spectrum of the electron moving in the neutron magnetic field considered as a spherical permanent magnet field. This means that the electron capture by the neutron is possible which, in turn, makes it possible to predict the neutrinoless neutron decay in which the captured electron plays the role of missing neutrino. Either produced electron can again undergo neutron capture, thus triggering a chain reaction, i.e., a certain cascade process. Such a chain reaction can be observed if it breaks. It is difficult to distinguish this break from the ordinary neutron beta decay, since the spatial and temporal resolution of modern detectors does not allow detection of cascade electrons.     

Magnetization distribution in magnetic films studied with Larmor-encoding

Additional information about the magnetization distribution in magnetic films is obtained with a 3D-polarimetry set-up. A pilot experiment was performed with the neutron polarization aligned perpendicular to the surface of a Fe-film in a magnetic field parallel to its surface. The Larmor-precession in the magnetic field between two current sheets was used to adjust the neutron polarization perpendicular to the sample surface. This new polarization-magnetization configuration was probed with a Fe-film in specular and off-specular scattering. The off-specular scattering is created by the magnetic domain structure of the Fe-film in remanence. The results of specular and off-specular scattering are reproduced by calculations for the configuration of the incoming neutron polarization parallel to the sample surface and the magnetic field and for the configuration of the incoming neutron polarization perpendicular to the sample surface and the magnetic field.     

强磁场中修正URCA过程的中微子产能率

基于n-p-e模型并考虑修正URCA过程中的质子分支,研究了强磁场对中子星核心区域修正URCA过程中微子产能率的影响.结果表明,强磁场使修正URCA过程的中微子产能率产生明显振荡;与中子分支相比,强磁场对质子分支中微子产能率的影响偏弱,但是它将提高总的中微子产能率.所得结论将有助于进一步研究中子星的冷却机理. 关键词： 中子星 强磁场 修正的URCA过程     

Interaction of neutrons with layered magnetic media in oscillating magnetic field

New experimental possibilities of investigating layered magnetic structures in oscillating magnetic fields are discussed. Spin-flip and nonspin-flip neutron reflection and transmission probabilities show a frequency dependency near the magnetic neutron resonance condition. This allows to increase the precision of the static magnetic depth profile measurements of the magnetized matter. Moreover, this opens new possibilities of measuring the induction of the oscillating field inside the matter and determining the magnetic susceptibility of the oscillating magnetic field. Refraction of neutrons as they pass through a magnetic prism in the presence of an oscillating magnetic field is also investigated. A non-polarized neutron beam splits into eight spatially separated neutron beams, whose intensity and polarization depend on the strength and frequency of the oscillating field. Also, it is shown that the oscillating magnetic permeability of an angstrom-thick layer can be measured with a neutron wave resonator.     

Microscopic calculation of the magnetic field of neutron stars

Based on the Dirac equation describing an electron moving in a uniform and cylindrically symmetric magnetic field which may be the result of the self-consistent mean field of the electrons themselves in a neutron star, we have obtained the eigen solutions and the orbital magnetic moments of electrons in which each eigen orbital can be calculated. From the eigen energy spectrum we find that the lowest energy level is the highly degenerate orbitals with the quantum numbers pZ=0, n=0, and m≥0. At the ground state, the electrons fill the lowest eigen states to form many Landau magnetic cells and each cell is a circular disk with the radius λfree and the thickness λe, where λfree is the electron mean free path determined by Coulomb cross section and electron density and λe is the electron Compton wavelength. The magnetic moment of each cell and the number of cells in the neutron star are calculated, from which the total magnetic moment and magnetic field of the neutron star can be calculated. The results are compared with the observational data and the agreement is reasonable.     

Experimental evidence of high-beta plasma confinement in an axially symmetric gas dynamic trap

In the axially symmetric magnetic mirror device gas dynamic trap (GDT), on-axis transverse beta (ratio of the transverse plasma pressure to magnetic field pressure) exceeding 0.4 in the fast ion turning points has been first achieved. The plasma has been heated by injection of neutral beams, which at the same time produced anisotropic fast ions. Neither enhanced losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. This observation confirms predicted magnetohydrodynamic stability of plasma in the axially symmetric mirror devices with average min-B, like the GDT is. The measured beta value is rather close to that expected in different versions of the GDT based 14 MeV neutron source for fusion materials testing.     

Order parameter of holmium in a magnetic field

The order parameter of the second order magnetic phase transition in Ho at 131 K has been measured in a magnetic field by neutron diffraction. It was expected that the applied field would change the number of components (n) of the order parameter from four to two. Such a change would be visible in the order parameter exponent β. However, in a field of 40 kOe, β is found to be 0.38 ± 0.02, in agreement with the zero field measurement and with an n = 4 model and in contradiction to an n = 2 model.     

Small-angle neutron scattering of nanocrystalline terbium with random paramagnetic susceptibility

We report magnetic small-angle neutron scattering (SANS) data for the nanocrystalline rare earth metal Terbium in its paramagnetic state. Whereas critical scattering dominates at large momentum transfer, q, the (magnetic-) field response of the scattering at small q arises from the spatial nonuniformity of the paramagnetic susceptibility tensor. The finding of an interrelation between SANS and the susceptibility suggests a way for characterizing the nonuniform magnetic interactions in hard magnets by neutron scattering.