Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The ...existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (n−n′) oscillation. Consequently, there were many experiments that have searched for n−n′ oscillation, and imposed constraints upon the parameters that describe it. Recently, further analysis on some of these results have identified anomalies which could point to the detection of n−n′ oscillation. All the previous efforts searched for n−n′ oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, n−n′ oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. Precession frequencies are measured, very precisely, by experiments searching for the electric dipole moment. For the first time, we used the data from the latest search for the neutron electric dipole moment to constrain n−n′ oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting 199Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to n−n′ oscillation. We thereby provide a lower limit on the n−n′ oscillation time constant of τnn′/|cos(β)|>5.7s,0.36T′<B′<1.01T′ (95% C.L.), where β is the angle between the applied magnetic field and the ambient mirror magnetic field. This constraint is the best available in the range of 0.36T′<B′<0.40T′.
While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of ...hypothetical neutron (n) to mirror-neutron (n′) transitions, it could not test all claimed signal regions at various mirror magnetic fields. Therefore, a new study of n−n′ oscillations using stored ultracold neutrons (UCNs) is underway at PSI, considerably expanding the reach in parameter space of mirror magnetic fields (B′) and oscillation time constants (τnn′). The new apparatus is designed to test for the anomalous loss of stored ultracold neutrons as a function of an applied magnetic field. The experiment is distinguished from its predecessors by its very large storage vessel (1.47 m3), enhancing its statistical sensitivity. In a test experiment in 2020 we have demonstrated the capabilities of our apparatus. However, the full analysis of our recent data is still pending. Based on already demonstrated performance, we will reach sensitivity to oscillation times τnn′/cos(β) well above a hundred seconds, with β being the angle between B′ and the applied magnetic field B. The scan of B will allow the finding or the comprehensive exclusion of potential signals reported in the analysis of previous experiments and suggested to be consistent with neutron to mirror-neutron oscillations.
The nEDM apparatus at PSI has been used to search for different dark
matter signatures utilizing its high sensitivity to shifts in the
neutron precession frequency and its well-controlled low ...magnetic field
at the
\mu
μ
T
level. Such a shift could be interpreted as a consequence of a
short-range spin-dependent interaction that could possibly be mediated
by axions or axion-like particles, or as an axion-induced oscillating
electric dipole moment of the neutron. Another search, based on
so-called UCN disappearance measurements, targeted previously reported
signals of neutron to mirror-neutron oscillations. These dark matter
searches confirmed and improved previous results, as detailed in this
review.
New aspects for high-intensity neutron beam production Mayer, Simon; Rauch, Helmut; Geltenbort, Peter ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2009, Letnik:
608, Številka:
3
Journal Article
Recenzirano
Neutron scattering is an important tool for the investigation of static and dynamic structures of matter. As it is an intensity limited technique, many attempts have been made to increase the ...effective beam intensity. High neutron intensities or, more precisely, high phase space densities of neutrons can be obtained at low energies only. Such ultra-cold neutrons can be trapped inside material and magnetic bottles. When neutrons of such densities become up-scattered, highly intense, monochromatic and pulsed beams can be produced, whose intensities can overcome limitations imposed by the classical neutron source strength. We report a recent experiment that demonstrated this alternative, to our knowledge, for the first time ever. Perspectives resulting from this development of highly intense neutron beam production will be discussed. A stationary ultra-cold neutron gas produced becomes transformed into a pulsed and monochromatic cold neutron beam.
In many neutron scattering instruments a convergent guide exit is used to increase the flux on the sample. But at the same time, the divergence of the neutrons increases. The resultant flux on the ...sample can increase or decrease depending on its distance to the guide exit and the sample size (relative to the guide size). An optimum can be expected for an intermediate convergence. It was our aim to find this optimum for different distances and samples sizes. Therefore, we have performed MC simulations with the software package VITESS. We combined it with a numerical method to find the optimal values. Different kinds of shapes were tested. The influences of starting values and criteria for the optimal exit were checked. For long wavelengths and great distances between exit and sample, the maximum was obtained by diverging exits and not by converging exits. Funnels with a kind of elliptical shape perform better than linearly converging ones. Significant gains can be reached by adapting exits to a certain wavelength range—at the cost of losses in other ranges.
Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion ...dark-matter field, when propagating on Earth’s trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modulates the spin precession of nuclear spins. Here we report on the null result of a demonstration experiment searching for a frequency modulation of the free spin-precession signal of 199Hg in a magnetic field. Our search covers the axion mass range
10^{-16} \textrm{eV} \lesssim m_a \lesssim 10^{-13} \textrm{eV}
10
−
16
eV
≲
m
a
≲
10
−
13
eV
and achieves a peak sensitivity to the axion-nucleon coupling of
g_{aNN} \approx 3.5 \times 10^{-6} \textrm{GeV}^{-1}
g
a
N
N
≈
3.5
×
10
−
6
GeV
−
1
.
Handling of polarization became very important in simulations of neutron scattering. One of the very comprehensive and open-source neutron simulation package, VITESS, has been intensely involved in ...polarized neutron simulations. Several examples will be shown here. Another similar package NISP also contains polarization tools. McStas has implemented an initial set of routines handling polarization, as our examples will also show.
Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The ...existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (\(n-n'\)) oscillation. Consequently, there were many experiments that have searched for \(n-n'\) oscillation, and imposed constraints upon the parameters that describe it. All the previous efforts searched for \(n-n'\) oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, \(n-n'\) oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. For the first time, we used the data from the latest search for the neutron electric dipole moment Phys. Rev. Lett. 124, 081803 (2020) to constrain \(n-n'\) oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting \(^{199}\)Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to \(n-n'\) oscillation. We thereby provide a lower limit on the \(n-n'\) oscillation time constant of \(\tau_{nn'}/\sqrt{|\cos(\beta)|} > 5.7~\)s, \(0.36~\mu\)T'\(<B'<1.01~\mu\)T' (95\% C.L.), where \(\beta\) is the angle between the applied magnetic field and the ambient mirror magnetic field. This constraint is the best available in the range of \(0.36~\mu\)T'\(<B'<0.40~\mu\)T'.
Primary neutron sources are based on research reactors and spallation sources whose peak fluxes are limited to values below 10
17
cm
−2
s
−1
1
,
2
. In this paper we present a method which can ...complement and improve the performance of existing and upcoming dedicated neutron sources
3
.
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