Search

Neutron polarization analysis (NPA) for small-angle neutron scattering (SANS) experiments using a pulsed neutron source was successfully achieved by applying a 3He spin filter as a spin analyzer for the neutrons scattered from the sample. The cell of the 3He spin filter gives a weak small-angle scattering intensity (background) and covers a sufficient solid angle for performing SANS experiments. The relaxation time of the 3He polarization is sufficient for continuous use for approximately 2 days, thus reaching the typical duration required for a complete set of SANS experiments. Although accurate evaluation of the incoherent neutron scattering, which is predominantly attributable to the extremely large incoherent scattering cross section of hydrogen atoms in samples, is difficult using calculations based on the sample elemental composition, the developed NPA approach with consideration of the influence of multiple neutron scattering enabled reliable decomposition of the SANS intensity distribution into the coherent and incoherent scattering components. To date, NPA has not been well established as a standard technique for SANS experiments at pulsed neutron sources such as the Japan Proton Accelerator Research Complex (J-PARC) and the US Spallation Neutron Source. It is anticipated that this work will contribute significantly to the accurate determination of the coherent neutron scattering component for scatterers in various types of organic sample systems in SANS experiments at J-PARC, particularly for systems involving competition between the coherent and incoherent scattering intensity.

A 3He spin filter is a useful device for polarizing a neutron beam. We are developing the 3He spin filters for users of the material and life science facility of the Japan Proton Accelerator Research Complex (J‑PARC). An in situ SEOP system with a 3He polarization evaluation system using nuclear magnetic resonance (NMR) method of adiabatic fast passage and electron paramagnetic resonance (EPR) was developed. We conducted an experiment on the neutron beam line BL10 (NOBORU) of J-PARC to confirm the consistency of 3He polarization, estimated using the neutron transmission, NMR and EPR. The polarization of 3He, evaluated using the different methods, was consistent and the evaluation system operated normally for about 6 h.

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.

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

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.

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 fundamental parity violation is enhanced by 10$^{6}$ times at maximum in several neutron induced compound nuclei. There is a theoretical prediction that fundamental T-violating effects can be also largely enhanced in compound nuclei implying that T-violation can be searched for by making very sensitive measurements. A T-violation search experiment using compound nuclei is planned at J-PARC. Polarized epithermal neutron beam, polarized nuclear target, and high count rate neutron detector are necessary for the experiment, and therefore a development of the neutron polarizer using polarized $^3$He is ongoing at J-PARC in JAEA. Recently, a clean vacuum system to fabricate $^3$He spin filters was constructed, and several $^3$He spin filters were fabricated. The current status of the development of the $^3$He spin filter was reported.

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.

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.

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.

There is a need for a high-counting-rate neutron detector in order to search for CP-violations using compound nucleus resonances. A pixel-type detector based on a Li-glass scintillator, called the LiTA detector, is one candidate for this search. We measured the performance of this detector at MLF, J-PARC, and confirmed that it is usable up to a counting rate of 0.8 Mcps/cm^2. A boron-loaded liquid scintillator is another candidate for the high-counting-rate detector. The 3.7 ns decay time of this scintillator is shorter than that of the Li-glass scintillator. However, this liquid scintillator is sensitive to both neutrons and gamma rays. Pulse-shape analysis to remove the undesired gamma-ray signals was attempted.

Angular distribution of individual $\gamma$-rays, emitted from a neutron-induced compound nuclear state via radiative capture reaction of ${}^{139}$La(n,$\gamma$) has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm L}-N_{\mathrm H})/(N_{\mathrm L}+N_{\mathrm H})$, where $N_{\mathrm L}$ and $N_{\mathrm H}$ are integrals of low and high energy region of a neutron resonance respectively, and we found that $A_{\mathrm{LH}}$ has the angular dependence of $(A\cos\theta_\gamma+B)$, where $\theta_\gamma$ is emitted angle of $\gamma$-rays, with $A= -0.3881\pm0.0236$ and $B=-0.0747\pm0.0105$ in 0.74 eV p-wave resonance. This angular distribution was analyzed within the framework of interference between s- and p-wave amplitudes in the entrance channel to the compound nuclear state, and it is interpreted as the value of the partial p-wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally we used the result to quantify the possible enhancement of the breaking of the time-reversal invariance in the vicinity of the p-wave resonance.

We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, $\phi'_{V_5} = [2.8\pm\,4.6(stat.)\pm\,4.0(sys.)]\times 10^{-5}~\mbox{rad/m}$ is consistent with zero. This result improves the upper bounds on the neutron-matter coupling $g_{A}^{2}$ from such an interaction by about three orders of magnitude for force ranges in the mm-$\mu$m regime., Comment: 10 pages, 3 figures

A possibility of new type experimental searches for new physics beyond the standard model is being introduced in the symmetry tests in neutron-induced compound states according to the successful operation of intense pulsed neutron sources. The basis of experiment design is discussed.

A modulated intensity by zero effort (MIEZE) spectrometer is a type of neutron-resonance spin-echo spectrometer and can be used to analyze the slow dynamics of condensed matter by measuring the intermediate scattering function I(Q,τ). A crucial feature of a MIEZE spectrometer is it leaves completely free the space between the sample and the detector because the sample is placed after the neutron-spin analyzer. Measuring the magnetic dynamics with a conventional neutron-spin-echo spectrometer is difficult, but with a MIEZE spectrometer such a measurement may be done simply by introducing a second analyzer after the sample. Measuring the magnetic dynamics with high precision requires the background to be reduced to a minimum and is a job for which a 3He neutron-spin filter (3He-NSF) is a promising candidate as a second analyzer. However, one difficulty with this approach is the diffusion of 3He gas from the 3He-NSF, which may be measured and interpreted as dynamics. Therefore, we investigate herein whether the dynamics of gas diffusion is detected when using a 3He-NSF as second analyzer in a MIEZE spectrometer. Toward this end, we experimented with the MIEZE spectrometer installed at beamline 06 (BL06) at the Materials and Life Science Experimental Facility at Japan Proton Accelerator Research Complex (J-PARC MLF). The results confirm that the gas-diffusion dynamics of the 3He-NSF are not detected, and that the 3He-NSF, therefore, can be used as a second analyzer in this MIEZE spectrometer.

It is theoretically suggested that the violation of charge conjugation and parity symmetry (CP-violation) could be enhanced in several compound nuclear reactions. According to the CPT theorem the violation of time-reversal symmetry (T-violation) would be enhanced too. The experimental sensitivity to find a T-violating effect in neutron-induced compound nuclear reactions depends on the value of a spin factor κ(J), which is a parameter specific for each nuclide. It can be determined from the angular dependence of γ-ray emission in (n,γ) reactions induced near a p-wave resonance. In this paper, the measurement result and the analysis status of experiments using the target nucleus 117Sn are reported.

The neutron spin rotation (NSR) collaboration used parity-violating spin rotation of transversely polarized neutrons transmitted through a 0.5 m liquid helium target to constrain weak coupling constants between nucleons. While consistent with theoretical expectation, the upper limit set by this measurement on the rotation angle is limited by statistical uncertainties. The NSR collaboration is preparing a new measurement to improve this statistically-limited result by about an order of magnitude. In addition to using the new high-flux NG-C beam at the NIST Center for Neutron Research, the apparatus was upgraded to take advantage of the larger-area and more divergent NG-C beam. Significant improvements are also being made to the cryogenic design. Details of these improvements and readiness of the upgraded apparatus are presented. We also comment on how recent theoretical work combining effective field theory techniques with the 1/Nc expansion of QCD along with previous NN weak measurements can be used to make a prediction for dϕ/dz in 4He. An experiment using the same apparatus with a room-temperature target was carried out at LANSCE to place limits on parity-conserving rotations from possible fifth-force interactions to complement previous studies. We sought this interaction using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The results of this measurement and its impact on the neutron-matter coupling gA2 from such an interaction are presented. The NSR collaboration is also preparing a new measurement that uses an upgraded version of the room-temperature target to be run on the NG-C beamline; and it is expected to constrain gA2 by at least two additional orders of magnitude for λc between 1 cm and 1 μm.

In this study, the germanium detector assembly, installed at the Accurate Neutron-Nuclear Reaction measurement Instruments (ANNRI) in the Material and Life Science Facility (MLF) operated by the Japan Proton Accelerator Research Complex (J-PARC), has been characterized for extension to the measurement of the angular distribution of individual gamma-ray transitions from neutron-induced compound states. We have developed a Monte Carlo simulation code using the GEANT4 toolkit, which can reproduce the pulse-height spectra of gamma-rays from radioactive sources and (n,gamma) reactions. The simulation is applicable to the measurement of gamma-rays in the energy region of 0.5-11.0 MeV.

Kota Kasahara∗, Shin-Hong Kim, Yuji Takeuchi, Ren Senzaki, Kazuki Nagata, Takuya Okudaira, Masahiro Kanamaru, Tatsuya Ichimura, Koya Moriuchi, Kenji Kiuchi, Yasuo Arai1, Masashi Hazumi1, Hirokazu Ikeda2, Shuji Matsuura2, Takehiko Wada2, Satoru Mima3, Hirokazu Ishino4, Takuo Yoshida5, Yukihiro Kato6, Erik Ramberg7, Mark Kozlovsky7, Paul Ruvinov7, Dmitri Segratskov7 University of Tsukuba, Ibaraki 305-8571, Japan 1KEK, Ibaraki 305-0801, Japan 2JAXA ISAS, Kanagawa 252-5210, Japan 3RIKEN, Saitama 351-0198, Japan 4Okayama University, Okayama 700-8530, Japan 5University of Fukui, Fukui 910-8507, Japan 6Kinki University, Osaka 577-8502, Japan 7Fermi National Accelerator Laboratory, Illinois, 60510, US E-mail: kasahara@hep.px.tsukuba.ac.jp

We present a proposal of an experiment for search for cosmic background neutrino decay. Due to the mass difference between neutrino generations, a heavier neutrino can decay into a lighter neutrino with a photon. Standard model predicts the neutrino lifetime is 10 44 year, while the current experimental lower limit of neutrino lifetime is 3 x10 12 year. However Left-Right symmetric model suggests much shorter neutrino lifetime down to 10 17 year in the shortest. If we assume a mass of the heaviest neutrino is 50 meV/c 2 , the expected photon energy at the neutrino rest frame is 25 meV. The energy spectrum of the photon from the cosmic background neutrino decay has a cutoff at this energy and a low energy tail due to a red shift effect as shown in Fig.1. Thus we propose an experiment to search for the photon emission from the decay of cosmic background neutrino by measuring the photon energy spectrum in the far infrared region with a superconducting tunneling junction (STJ) detector. We plan to perform a rocket experiment with the STJ detector in 2016 in the earliest, aiming at improving the neutrino lifetime limit by two order. We also aim at a 10-hour satellite experiment with 5 sensitivity for the neutrino lifetime of 10 17 year in further future [1]. [1] S. H. Kim, K. Takemasa, Y. Takeuchi and S. Matsuura, J. Phys. Soc. Jpn., 81 (2012) 024101S.

Large enhanced P-violations was discovered in several compound nuclei. A mechanism of P- violation can be applied to enhancement of T-violation in compound nucleus. We plan the experi- ment for sensitive T-violation search, however, the mechanism of P-violation(s-p mixing) has not been verified in detail yet and the spin factor κ(J) has not been measured in candidate nuclei for T-violation search. We need to measure angular distributions in the (n,γ) reaction for verification of s-p mixing and determination of κ(J) as a feasibility study for the T-violation search. The (n,γ) reaction of 139La which is one of the candidate nuclei was measured with 4π germanium spectrometer in J-PARC/MLF/ANNRI. A neutron spectrum and a γ-ray spectrum for 139La was obtained.

Large enhanced P violation in a nuclear resonance reaction has been observed by using a polarized neutron beam. Enhanced CP violation is predicted to exist within the same nuclear reaction. We are now preparing to supply a polarized neutron beam for a CP violation search experiment. In the enhancement process of CP violation, we assume that the P violation of the compound nuclear state doesn’t depend on the final state. However this assumption has not been verified yet. We plan to verify the assumption by measuring the $^{139}\rm La$(n,$\gamma$) reaction with a polarized neutron beam at J-PARC MLF BL04. The supplied neutron beam will be polarized by using $^{3}$He spin filter, which will be installed into BL04. We present the states of development for $^{3}$He spin filter and study of the equipment in BL04.