Search

The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric dipole moment (nEDM) measurement with an uncertainty of $10^{-27}\,e\cdot\mathrm{cm}$, which is an order-of-magnitude better than the current nEDM upper limit and enables us to test Supersymmetry. To achieve this precision, we are developing a new high-intensity ultracold neutron (UCN) source using super-thermal UCN production in superfluid helium (He-II) and a nEDM spectrometer. The current development status of them is reported in this article., Comment: Proceedings of the 24th International Spin Symposium (SPIN 2021), 18-22 October 2021, Matsue, Japan

Structure factors describe how incident radiation is scattered from materials such as silicon and germanium and characterize the physical interaction between the material and scattered particles. We use neutron pendell\"{o}sung interferometry to make precision measurements of the (220) and (400) neutron-silicon structure factors, and achieve a factor of four improvement in the (111) structure factor uncertainty. These data provide measurements of the silicon Debye-Waller factor at room temperature and the mean square neutron charge radius $\langle r_n^2 \rangle = -0.1101 \pm 0.0089 \, \mathrm{fm}^2$. Combined with existing measurements of the Debye-Waller factor and charge radius, the measured structure factors also improve constraints on the strength of a Yukawa-modification to gravity by an order of magnitude over the 20 pm to 10 nm length scale range.

The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration aims to search for the neutron electric dipole moment (nEDM) with unprecedented precision. One of the essential elements for the nEDM measurement is a polarization analyzer of ultracold neutrons (UCNs), whose main component is a magnetized thin iron film. Several thin iron films were deposited on aluminum and silicon ubstrates and were characterized by vibrating sample magnetometry and cold-neutron reflectometry. A magnetic field required to saturate the iron film is $\sim$12 kA/m for those on the aluminum substrates and 6.4 kA/m for the silicon substrates. The magnetic potential of the iron films on the Si substrate was estimated to be 2 T by the neutron reflectometry, which is sufficient performance for an UCN polarization analyzer of the nEDM measurement., Proceedings of the 24th International Spin Symposium (SPIN 2021), 18-22 October 2021, Matsue, Japan

An interferometer design that cancels all displacement noises of its test masses and maintains a gravitational-wave (GW) signal by combining multiple detector signals is called a displacement noise-free interferometer (DFI). The idea has been considered previously for a laser interferometer. However, a limitation of a laser DFI is that its sensitive frequency band is too high for astrophysical GW sources, $\sim 10^5\,{\rm Hz}$ even for a kilometer-sized interferometer. To circumvent this limitation, in this paper, we propose a neutron DFI, in which neutrons are used instead of light. Since neutrons have velocities much lower than the speed of light, the sensitive frequency band of a neutron DFI can be lowered down to $\sim 10^{-1}\,{\rm Hz}$. Therefore, a neutron DFI can be utilized for detecting GWs that are inaccessible by an ordinary laser interferometer on the ground., 7 pages, 5 figures. Published version in Physical Review D

Neutron imaging is a nondestructive inspection technique that has a wide range of applications. One of the important aspects of neutron imaging is achieving a micrometer-scale spatial resolution. The development of a high-resolution neutron detector is a challenging task. As one potential solution to this task, we investigate whether neutron detectors based on fine-grained nuclear emulsions are suitable for high-resolution neutron imaging applications. High track density is necessary to improve the quality of neutron imaging. However, the available track analysis methods are difficult to apply under high track density conditions. Simulated images are used to determine the required track density for neutron imaging. A track density of the order of [Formula: see text] tracks per [Formula: see text] is sufficient to utilize neutron detectors for imaging applications. Contrast resolution was also investigated for image datasets with various track densities and neutron transmission rates. Moreover, experiments were performed for the neutron imaging of gadolinium-based gratings with known geometries. The grating structures were successfully resolved. The calculated [Formula: see text] 10%–90% edge response using the grayscale optical images of the grating slit with a periodic structure of 9 [Formula: see text]m was [Formula: see text] [Formula: see text]m.

The improvement of sensitivity to gravitational waves (GWs) at lower frequencies is still challenging on account of displacement noise. One of the solutions is the neutron displacement-noise-free interferometer (DFI). We focus on a simplification of the detector configuration by taking advantage of the ability to adjust the neutron speed depending on the configuration. The new configuration consists of two beamsplitters and two mirrors, which constitute a single Mach-Zehnder interferometer (MZI). It is simpler than the configuration with two MZIs in previous research. All displacement noise of mirrors and beamsplitters can be canceled in the frequency domain. This cancellation can be explained intuitively using a phasor diagram., Comment: 12 pages, 5 figures

Neutron imaging is a non-destructive inspection technique with a wide range of potential applications. One of the key technical interests concerning neutron imaging is to achieve micrometer-scale spatial resolution. However, developing a neutron detector with a high spatial resolution is a challenging task. Recent efforts are focused on achieving this milestone or even submicrometer spatial resolution. Herein, we introduce our technique for neutron imaging using a fine-grained nuclear emulsion and evaluate the spatial resolution. We used the fine-grained nuclear emulsion with a gadolinium-based Siemens star test pattern and a grating with a periodic structure of 9 μm. The deduced value of the spatial resolution is less than 1 μm using the developed technique. To the best of our knowledge, the submicrometer spatial resolution that we achieved using our method is the best among all reported neutron imaging devices.

Fluorescent nuclear track detectors (FNTDs) based on Al${_2}$O${_3}$:C,Mg crystals are luminescent detectors that can be used for dosimetry and detection of charged particles and neutrons. These detectors can be utilised for imaging applications where a reasonably high track density, approximately of the order of 1 $\times$ $10^4$ tracks in an area of 100 $\times$ 100 $\mu$m$^2$, is required. To investigate the reusability of FNTDs for imaging applications, we present an approach to perform optical bleaching under the required track density conditions. The reusability was assessed through seven irradiation-bleaching cycles. For the irradiation, the studied FNTD was exposed to alpha-particles from an $^{241}$Am radioactive source. The optical bleaching was performed by means of ultraviolet laser light with a wavelength of 355 nm. Three dedicated regions on a single FNTD with different accumulated track densities and bleaching conditions were investigated. After every irradiation-bleaching cycle, signal-to-noise ratio was calculated to evaluate FNTD performance. It is concluded that FNTDs can be reused at least seven times for applications where accumulation of a high track density is required.

Neutron energy-dependent angular distributions were observed for individual $\ensuremath{\gamma}$ rays from the 0.74 eV $p$-wave resonance of $^{139}\mathrm{La}+n$ to several lower excited states of $^{140}\mathrm{La}$. The $\ensuremath{\gamma}$-ray signals were analyzed in a two-dimensional histogram of the $\ensuremath{\gamma}$-ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual $\ensuremath{\gamma}$ rays. The angular distribution was also found for a photopeak accompanied with a faint $p$-wave resonance component. Our results can be interpreted as interference between $s$- and $p$-wave amplitudes, which may be used to study discrete symmetries of fundamental interactions.

The construction is described of a monolithic thick-crystal perfect silicon neutron interferometer using an ultra-high-precision grinding technique and a combination of annealing and chemical etching that differs from the construction of prior neutron interferometers. The interferometer is the second to have been annealed after machining and the first to be annealed prior to chemical etching. Monitoring the interference signal at each post-fabrication step provides a measurement of subsurface damage and its alleviation. In this case, the strain caused by subsurface damage manifests itself as a spatially varying angular misalignment between the two relevant volumes of the crystal and is reduced from ∼10−5 rad to ∼10−9 rad by way of annealing and chemical etching.

A neutron decays into a proton, an electron, and an anti-neutrino through the beta-decay process. The decay lifetime ($\sim$880 s) is an important parameter in the weak interaction. For example, the neutron lifetime is a parameter used to determine the |$V_{\rm ud}$| parameter of the CKM quark mixing matrix. The lifetime is also one of the input parameters for the Big Bang Nucleosynthesis, which predicts light element synthesis in the early universe. However, experimental measurements of the neutron lifetime today are significantly different (8.4 s or 4.0$\sigma$) depending on the methods. One is a bottle method measuring surviving neutron in the neutron storage bottle. The other is a beam method measuring neutron beam flux and neutron decay rate in the detector. There is a discussion that the discrepancy comes from unconsidered systematic error or undetectable decay mode, such as dark decay. A new type of beam experiment is performed at the BL05 MLF J-PARC. This experiment measured neutron flux and decay rate simultaneously with a time projection chamber using a pulsed neutron beam. We will present the world situation of neutron lifetime and the latest results at J-PARC., Comment: 8 pages, 6 figures, Proceedings of J-PARC Symposium 2019

A neutron detector using a fine-grained nuclear emulsion has a sub-micron spatial resolution and thus has potential to be applied as high-resolution neutron imaging. In this paper, we present two approaches to applying the emulsion detectors for neutron imaging. One is using a track analysis to derive the reaction points for high resolution. From an image obtained with a 9 &mu, m pitch Gd grating with cold neutrons, periodic peak with a standard deviation of 1.3 &mu, m was observed. The other is an approach without a track analysis for high-density irradiation. An internal structure of a crystal oscillator chip, with a scale of approximately 30 &mu, m, was able to be observed after an image analysis.

The violation of baryon number, B , is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the Universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR program is a proposed two-stage experiment at the European Spallation Source to search for baryon number violation. The program will include high-sensitivity searches for processes that violate baryon number by one or two units: free neutron–antineutron oscillation ( n → n ̄ ) via mixing, neutron–antineutron oscillation via regeneration from a sterile neutron state ( n → [ n ′ , n ̄ ′ ] → n ̄ ), and neutron disappearance (n → n′); the effective Δ B = 0 process of neutron regeneration ( n → [ n ′ , n ̄ ′ ] → n ) is also possible. The program can be used to discover and characterize mixing in the neutron, antineutron and sterile neutron sectors. The experiment addresses topical open questions such as the origins of baryogenesis and the nature of dark matter, and is sensitive to scales of new physics substantially in excess of those available at colliders. A goal of the program is to open a discovery window to neutron conversion probabilities (sensitivities) by up to three orders of magnitude compared with previous searches. The opportunity to make such a leap in sensitivity tests should not be squandered. The experiment pulls together a diverse international team of physicists from the particle (collider and low energy) and nuclear physics communities, while also including specialists in neutronics and magnetics.

The neutron lifetime has been measured by comparing the decay rate with the reaction rate of $^3$He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the $^3$He(n,p)$^3$H reaction using a gas chamber of which working gas contains diluted $^3$He. The measured neutron lifetime was $898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$s., 28 pages, 20 figures, will be submitted to PTEP

We are developing a neutron polarizer with polarized $^3$He gas, referred to as a $^3$He spin filter, based on the Spin Exchange Optical Pumping (SEOP) for polarized neutron scattering experiments at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). A $^3$He gas-filling station was constructed at J-PARC, and several $^3$He cells with long spin relaxation times have been fabricated using the gas-filling station. A laboratory has been prepared in the MLF beam hall for polarizing $^3$He cells, and compact pumping systems with laser powers of 30~W and 110~W, which can be installed onto a neutron beamline, have been developed. A $^3$He polarization of 85% was achieved at a neutron beamline by using the pumping system with the 110~W laser. Recently, the first user experiment utilizing the $^3$He spin filter was conducted, and there have been several more since then. The development and utilization of $^3$He spin filters at MLF of J-PARC are reported., Comment: 9 pages, 15 figures

The $\mathrm{Nd}^{3+}$ doped $\mathrm{LaAlO}_3$ crystal is a good candidate of a polarized $^{139}\mathrm{La}$ target for the search of the P-odd and T-odd interaction in the low-energy neutron absorption of $^{139}\mathrm{La}$. As the first step for realizing the polarized $^{139}\mathrm{La}$ target, we grow the undoped $\mathrm{LaAlO}_3$ crystal and the $\mathrm{La}_{1-x}\mathrm{Nd}_x\mathrm{AlO}_3$ ($x=5 \times 10^{-4}$) crystal by floating-zone method with four halogen lamps. The ESR measurements of $\mathrm{Nd}^{3+}$ in the latter crystal indicated that the linewidth was about 6 gauss, whose value is the same as the crystal in which 50 % $^{139}\mathrm{La}$ polarization was achieved in the previous DNP experiment. As the result, the crystals grown by this method can be applicable to the target study for the T-violation search.

A neutron lifetime measurement conducted at the Japan Proton Accelerator Research Complex (J-PARC) is counting the number of electrons from neutron decays with a time projection chamber (TPC). The $\gamma$ rays produced in the TPC cause irreducible background events. To achieve the precise measurement, the inner walls of the TPC consist of $^6$Li-enriched lithium-fluoride ($^6$LiF) tiles to suppress the amount of $\gamma$ rays. In order to estimate the amount of $\gamma$ rays from the $^{6}{\rm LiF}$ tile, prompt gamma ray analysis (PGA) measurements were performed using germanium detectors. We reconstructed the measured $\gamma$-ray energy spectrum using a Monte Carlo simulation with the stripping method. Comparing the measured spectrum with a simulated one, the number of $\gamma$ rays emitted from the$^{6}{\rm LiF}$ tile was $(2.3^{+0.7}_{-0.3}) \times 10^{-4}$ per incident neutron. This is $1.4^{+0.5}_{-0.2}$ times the value assumed for a mole fraction of the $^{6}{\rm LiF}$ tile. We concluded that the amount of $\gamma$ rays produced from the $^{6}{\rm LiF}$ tile is not more twice the originally assumed value., Comment: 14 pages, 11 figures, will be submitted to JINST

The measurement of the ground state hyperfine structure of muonic helium has the potential to improve the precision of the mass of the negative muon by a factor of 50 or more. The mass of the negative muon is very important because it enables us to test the CPT theorem by comparison with positive muon mass. We aim to measure the hyperfine structure of muonic helium with a precision 1000 times higher than previous experiments [1,2] using the highintensity muon beam at J-PARC and have already obtained results better than the current precision in zero-field measurements in a test experiment in March 2021. To further improve the precision, we plan to measure in a high magnetic field and incorporate a technique that can produce highly polarized muonic helium atom [3]. In this paper, we will report on these developments.

For flow visualization study of quantum turbulence in superfluid $$^4$$ He, He $$_2^*$$ excimers are unique tracers which follow only normal-fluid component flow above 1 K. To generate detectable small He $$_2^*$$ clouds (clusters) required for full-space velocity field measurements, we have adopted a new method based on neutron absorption reaction of $$^3$$ He impurities in $$^4$$ He and conducted proof-of-principle experiments. Generation of the He $$_2^*$$ excimers was detected by laser-induced fluorescence using photomultiplier tubes. The fluorescence was observed to increase proportionally to the neutron flux, suggesting that a sufficient amount of He $$_2^*$$ excimers were generated by neutrons. We also estimated the number of He $$_2^*$$ excimers possibly generated by $$\gamma $$ -rays and found that the relevant contribution was less than 40%. Thus, the majority of the He $$_2^*$$ excimers was confirmed to be generated via n- $$^3$$ He absorption reactions.

A new type of cold/ultracold neutron detector that can realize a spatial resolution of less than 100 nm was developed using nuclear emulsion. The detector consists of a fine-grained nuclear emulsion coating and a 50-nm thick 10B4C layer for the neutron conversion. The detector was exposed to cold and ultracold neutrons (UCNs) at the J-PARC. Detection efficiencies were measured as (0.163 ± 0.015 (stat) ± 0.013 (sys))% and (10.3 ± 1.3 (stat) ± 1.1 (sys))% for cold and ultracold neutrons consistently with the 10 B content in the converter. Positions of individual neutrons can be determined by observing secondary particle tracks recorded in the nuclear emulsion. The spatial resolution of incident neutrons were found to be in the range of 11–99 nm in the angle region of tan θ≤1.9 , where θ is the angle between a recorded track and the normal direction of the converter layer. The achieved spatial resolution corresponds to the improvement of one or two orders of magnitude compared with conventional techniques and it is comparable with the wavelength of UCNs., 素粒子用写真技術を応用した超高分解能新型中性子検出器の開発に成功 --中性子の波紋を撮ってこの世の成り立ちに迫る--. 京都大学プレスリリース. 2018-11-21.

Pendellösung interferometry is one of the technique for accurate determination of the structure factors of crystals. Observation method of Pendellösung fringes by using pulsed cold neutrons and the time-of-flight analysis were established. We measured the nuclear scattering length of silicon by the Pendellösung fringes with pulsed neutrons as (4.125±0.003(stat:)±0:028(syst:)). This indicates the applicability of Pendellösung interferometry at high-intensity pulsed neutron facilities for various precision measurements., ファイル公開：2020-11-11, Corrigendum to “Pendellösung interferometry by using pulsed neutrons” [Nucl. Instrum. Methods Phys. Res. A 908 (2018) 78–81]: https://doi.org/10.1016/j.nima.2018.10.218 (http://hdl.handle.net/2237/29267)

The nuclear spin-lattice relaxation time ($T_1$) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer $T_1$ under lower magnetic field and at higher temperature. The $T_1$ of $^{139}{\rm La}$ and ${}^{27}{\rm Al}$ was measured under magnetic fields of $0.5$-$2.5$ T and at temperatures of $0.1$-$1.5$ K and found widely distributed up to 100 h. The result suggests that the $T_1$ can be as long as $T_1 \sim$ 1 h at $0.1$ K with a magnetic field of $0.1$ T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer $T_1$ are discussed., Comment: 10 pages, 8 figures

A neutron guide system for neutron resonance spin echo spectrometers has been constructed at BL06 of the Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility....

We report the first experimental test of TOF-MIEZE technique using very cold neutrons (VCNs) towards high-resolution quasi-elastic neutron scattering spectroscopy . TOF-MIEZE is a type of neutron resonance spin echo spectroscopy with a combination of the time-of-flight (TOF) method and modulation of intensity by zero effort (MIEZE). A compact MIEZE instrument was constructed at the VCN beam port at the High Flux Reactor at the Institut Laue Langevin. By accumulating individual oscillations of raw data, we observed a TOF-MIEZE signal with an effective frequency of 50 kHz in a wavelength band of 4–6 nm. The signal contrasts were 0.59 ± 0.04 and 0.29 ± 0.03 for wavelengths of 4 nm and 6 nm, respectively. The Fourier time was estimated to be 70 ns with 6 nm VCNs in the experimental set-up.

We developed a neutron detector with submicron spatial resolution by incorporating 6 Li into a fine-grained nuclear emulsion. Upon exposure to thermal neutrons, tracks from neutron capture events were observed. The detector spatial resolution was estimated from their grain density. Detection efficiency was measured using the detector response to cold neutrons.

Precision measurements of slow neutron cross sections with atoms have several scientific applications. In particular, the $n\text{\ensuremath{-}}^{4}\mathrm{He}$ $s$-wave scattering length is important to know both for helping to constrain the nuclear three-body interaction and for the proper interpretation of several ongoing slow neutron experiments searching for other types of neutron-atom interactions. We present new measurements of the ratios of the neutron differential scattering cross sections of the noble gases He, Ar, Kr, and Xe to Ne. All gases used were of natural isotopic abundance. These measurements were performed using a recently developed neutron-scattering apparatus for gas samples located on a pulsed slow neutron beamline which was designed to search for possible exotic neutron-atom interactions and employs both neutron time of flight information and a position-sensitive neutron detector for scattering event reconstruction. We found agreement with the literature values of scattering cross sections inferred from Ar/Ne, Kr/Ne, and Xe/Ne differential cross-section ratios over the $q$ range of 1--7 ${\mathrm{nm}}^{\ensuremath{-}1}$. However, for the case of He/Ne we find that the cross section inferred differs by 11.3% ($7.6\ensuremath{\sigma}$) from previously reported values inferred from neutron phase-shift measurements, but is in reasonable agreement with values from other measurements. The very large discrepancy in the He/Ne ratio calls for a new precision measurement of the $n\text{\ensuremath{-}}^{4}\mathrm{He}$ scattering length using neutron interferometry.

Large sources of parity violation have been observed in compound nuclear reactions. These enhancements are described by the compound nuclear model, which can be used to describe the angular correlation of $\gamma$-rays produced in $(\rm{n},\gamma)$ reactions in medium-heavy nuclei. It has also been suggested that these same reactions could lead to a similar enhancement in time reversal violating processes. Therefore, we are interested in verifying the compound nuclear model by studying the $(\rm{n},\gamma)$ reaction using polarized neutrons. In this paper, we discuss the installation and characterization of a neutron polarizer used in the $(\rm{n},\gamma)$ measurement with transversely polarized neutrons.

The neutron is suitable for precision measurements to search for new physics. Extremely-high intense pulsed neutron provided by J-PARC enable us to perform new type of precision measurements. We are performing various experiments with low energy neutrons at J-PARC. In this paper, we describe our experimental search for time reversal symmetry violation in nuclear reactions. The enhancement of the T-violation is predicted in the neutron capture reaction for some nuclei. Our recent results of 139La(n, gamma) reaction suggested that the enhancement is large enough to search T-violation with high sensitivity, which can be reach to that of neutron EDM and which has different systematics. In J-PARC, we are also performing the precision measurement of neutron lifetime and medium-range unknown force search by using pulsed neutrons. We are continuing researches and developments, for example, search for neutron electric dipole moment by using neutron diffraction with non-centrosymmetric crystal and a chameleon field search with neutron interferometer.

In a neutron lifetime measurement at the Japan Proton Accelerator Complex, the neutron lifetime is calculated from the neutron decay rate and the incident neutron flux. The flux is obtained by counting the protons emitted from the neutron absorption reaction of ${}^{3}{\rm He}$ gas, which is diluted in a mixture of working gas in a detector. Hence, it is crucial to determine the amount of ${}^{3}{\rm He}$ in the mixture. In order to improve the accuracy of the number density of the ${}^{3}{\rm He}$ nuclei, we have suggested using the ${}^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ reaction as a reference because this reaction involves similar kinetic energy to the $^3$He(n,p)$^3$H reaction and a smaller reaction cross section to introduce reasonable large partial pressure. The uncertainty of the recommended value of the cross section, however, is not satisfied with our requirement. In this paper we report the most accurate experimental value of the cross section of the $^{14}$N(n,p)$^{14}$C reaction at a neutron velocity of 2200 m s$^{-1}$, measured relative to the $^3$He(n,p)$^3$H reaction. The result was 1.868 $\pm$ 0.003 (stat.) $\pm$ 0.006 (sys.) b. Additionally, the cross section of the $^{17}$O(n,$\alpha$)$^{14}$C reaction at the neutron velocity is also redetermined as 249 $\pm$ 6 mb.

We performed a polarized neutron transmission asymmetry measurement utilizing the 139La(n,γ)140La reaction. This measurement involved the use of a recently developed 3He spin filter mounted on the J-PARC MLF beam line number 4 (BL04). The resulting value of the longitudinal asymmetry AL = (11.7 ± 1.1)% was found to be in good agreement with existing values in the literature suggesting that the method by which we polarize the neutron beam is not a significant source of uncertainty. This preliminary work represents a first step toward future measurements of the angular correlation in (n̅,Υ) reactions necessary in the search for enhanced T-Violation in compound nuclei.

High precision measurements of the ground state hyperfine structure (HFS) of muonium is a stringent tool for testing bound-state quantum electrodynamics (QED) theory, determining fundamental constants of the muon magnetic moment and mass, and searches for new physics. Muonium is the most suitable system to test QED because both theoretical and experimental values can be precisely determined. Previous measurements were performed decades ago at LAMPF with uncertainties mostly dominated by statistical errors. At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is planning complementary measurements of muonium HFS both at zero and high magnetic field. The new high-intensity muon beam that will soon be available at H-Line will provide an opportunity to improve the precision of these measurements by one order of magnitude. An overview of the different aspects of these new muonium HFS measurements, the current status of the preparation for high-field measurements, and the latest results at zero field are presented.

Parity violating effects enhanced by up to 106 times compared to proton-proton scattering have been observed in several neutron capture induced compound nuclei. This enhancement is explained as an interference between an s-wave and a p-wave amplitude (s-p mixing). Theory predicts that this mechanism can also enhance T-violating effects. For estimation of this enhancement in a promising candidate nucleus, we measured the angular distribution of γ-rays in the (n,γ) reaction induced in a 139La target. Experiments were performed at J-PARC, using a germanium detector array at an intense neutron beam. Analysis of the observed angular dependence around the 0.74 eV p-wave resonance allowed us to determine the ratio of the partial p-wave neutron width to the total neutron width in the entrance channel of the compound nucleus. We also report our development of a 3He spin filter needed as an epithermal-neutron polarizer for the T-violation search.

The decay lifetime of free neutrons (∼880 s) is an important parameter of the weak interaction and for Big Bang Nucleosynthesis. However, results of measurements currently show discrepancies depending on the method used. As most experiments nowadays employ ultra cold neutrons, we have developed a new cold-beam experiment which we perform at the Japan Proton Accelerator Research Complex. As a special feature, a polarized neutron beam is bunched by a spin flip chopper. A time projection chamber operated with He and CO2gas, including a well-controlled amount of3He, is used for detection of the beta-decays and simultaneous determination of the beam intensity. Using the data between 2014 and 2016, we evaluated our first, preliminary result of the neutron lifetime as 896 ± 10(stat.)−10+14(sys.) s. We plan several upgrades to achieve our precision goal of 1 s.

It is known that parity violation can be enhanced in compound nuclei due to mixing of s- and p-waves, and it is suggested that time reversal invariance (T) violation is enhanced by the same mechanism. We are planing a T-violation search using compound nuclei produced in neutron capture reactions. Although 81Br is one of the candidate target nuclei, its sensitivity to T-violation has not yet been determined. For an estimate of the latter, a measurement of the angular distribution of γ-rays emitted in the 81Br(n,γ) reaction was carried out in November 2017, of which we report first results.

This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron-antineutron oscillations, and suggests avenues for future improvement in the experimental sensitivity., Comment: Submitted to Physics Reports

The International Conference on Neutron Optics (NOP2017) was held in Nara, Japan at the Nara Kasugano International Forum from July 5 to 8, 2017, as a satellite conference prior to the Internationa...