Session 1WCB: Neutron Fundamental Physics II

Neutron Fundamental Physics Workshop: TBD

TBD   

Search for new interaction in the sub-micron range with small-angle neutron scattering

Unknown gravitylike interactions, i.e. new interactions coupling to mass, with sub-millimeter ranges are recently attracting considerable interests, since it is suggested by the large-extra-dimension (LED) models which provide a possible solution for so-called hierarchy problem in the elementally particle physics[1]. So far, such new interactions have been searched with Cavendish-type experiments using torsion pendulum and so on. The sensitivities of those experiments, however, become smaller below a few micrometers due to serious background caused by inter-molecular forces whose strength is proportional to the electric polarizabilities of the test objects. The small-angle neutron scattering (SANS) is considered useful for probing new gravity-like interactions in sub-micron range thanks to an extremely small electric polarizability of the neutron. Previously, SANS experiments with noble gas targets were performed[2,3]. The coupling constant suggested by the theories is, however, far below the sensitivities of those experiments. To improve the experimental sensitivity, we are promoting the SANS experiment using the targets made of nanoparticles[4] in the series of the experiments 2019A0225, 2019B0339, 2020B0416, 2022A0253, and 2022B0333 at Materials and Life-science experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). In the case of neutron scattering with nanoparticle target, since the coherent scattering intensity is enhanced by a factor of ~10⁶ which corresponds to the number of atoms contained in a particle, a drastic improvement of the sensitivity to new interactions is expected. The key to the present method is the suppression of the background caused by the nuclear coherent scattering which is also enhanced. Therefore, we are developing the nanoparticles made of the elements or isotopes with opposite signs of coherent scattering length. This paper will report the present status of the target development and the SANS experiment.   

Beam-based Neutron Lifetime Measurements at NIST: BL2 and BL3

Neutron beta decay is the simplest example of nuclear beta decay and is crucial in our understanding of weak processes. The neutron lifetime, when combined with other neutron decay parameters, provides a test of the unitarity of the CKM matrix in the Standard Model; is an important input in Big Bang Nucleosynthesis models; and plays a role in other areas including solar physics and the detection of reactor antineutrinos. Competitive tests of unitarity in the CKM matrix require determination of the neutron lifetime to better than 0.3 s. While the most precise neutron lifetime experiments have reached uncertainties of less than 1 s, the current 10 s discrepancy between bottle and beam-based determinations presents a challenge.

In this talk I will discuss our efforts to address this discrepancy via the ongoing BL2 beam-based neutron lifetime experiment at NIST. I will also provide an update on the next-generation beam lifetime experiment, BL3, currently under construction. The goal of BL3 is to achieve < 0.3 s uncertainty utilizing the beam method.   

Applications of quantum random walk and dynamical diffraction for particle and nuclear physics

Even though the Standard Model of particle physics over the years demonstrated a large success in experimental predictions, we are in the constant search for its limitation and extensions. One example of such extension would be the existence of a fifth force. The recent experiment based on neutron interferometry, specifically Pendellösung interferometry, that is usually explained by Dynamical Diffraction (DD) theory of neutron scattering placed the most stringent bound on the strength of a such fifth force. Unfortunately, this DD theory is often hard to use in non-ideal cases where interferometers might have surface roughness or crystal imperfections and impurities. Using the quantum information model of dynamical diffraction, we consider a neutron cavity composed of two perfect crystal silicon blades capable of containing the neutron wavefunction. We show that the internal confinement of the neutrons through Bragg diffraction can be modelled by a quantum random walk. Furthermore, we introduce a toolbox for modelling crystal imperfections such as surface roughness and defects. Good agreement is found between the simulation and the experimental implementation, where leakage beams are present, modelling of which is impractical with the conventional theory of dynamical diffraction. Analysis of the standing neutron waves is presented in regards to the crystal geometry and parameters; and the conditions required for well-defined bounces are derived. The presented results enable new approaches to studying the setups utilizing neutron confinement, such as the experiments to measure neutron magnetic and electric dipole moments.