Session 2WB: Frontiers in Neutron Physics II

Neutron conversions to antineutrons and sterile neutrons

Searches for free neutrons converting to antineutrons and/or sterile neutrons play a distinctive role in the program of baryon number violation searches. These searches test a global symmetry of the Standard Model that must be violated to generate the observed matter-antimatter asymmetry in the universe and offer a unique portal to a dark sector. There is increasing interest in searches for ``mirror'' and other dark neutrons as a possible component of dark matter or as a solution to the so-called "neutron lifetime anomaly". A diverse, ongoing suite of experimental studies and new experimental efforts have been proposed to probe these phenomena. Small-scale searches for neutron oscillations also provide a chance for technical development which will inform future high-sensitivity searches for free neutron-antineutron oscillation searches, which could illuminate the process by which our universe evolved to contain only matter. Next generation neutron sources such as the European Spallation Source and kilo-ton-scale detectors such as the Deep Underground Neutrino Experiment, as well as other new concepts and technological advances, create a timely opportunity to enhance the sensitivity of such a search compared to previous limits by three orders of magnitude or more. Here, we will review current efforts worldwide to search for these rare processes and the bright outlook for this burgeoning field.   

Search for new short range forces with cold and ultracold neutrons

Various models for new physics, motivated e.g. by the attempt explain the energy content of the universe, predict the existence of new interactions with a range of nanometers to millimeters. The free neutron is a suitable probe for such interactions, being insensitive to background from a much stronger electrostatic interaction. In my talk, I will present various recent and future measurements that have used the neutron as a probe. I will include neutron interferometry, gravity resonance spectroscopy, and neutron scattering.   

Fundamental physics and materials science enabled by multi-scale and multi-modal neutron imaging

In this talk we'll discuss how the properties of the neutron provide a diverse set of interactions with matter and fields, yielding unique image contrasts. Since neutron interact primarily via the strong nuclear force and are net electrically neutral, neutrons readily penetrate through centimeters of many common metals, lead being especially transparent in stark contrast to X-rays. We exploit the different views offered by neutrons and X-rays to capture simultaneous tomography data sets which allows for facile discrimination of material phases within heterogeneous materials, such as concrete, shale, and batteries [1]. The intrinsic spin of the neutron allows one to image bulk magnetic fields; exploiting v x E, one can even image the electric field distribution due to the finite spin rotation [2]. Grating interferometry further expands the possibilities. Using a long baseline interferometer enabled by the 3-grating far-field geometry, one has the potential to make a competitive measurement of the Newtonian gravitational constant [3]. Meanwhile, the 2-grating field geometry allows one to measure, in each pixel or voxel, the pair-correlation function of a system, resulting in data sets that span the nm to cm [4]. References: [1] J.M. LaManna et al, RSI 88, 113702 (2017); DOI: 10.1063/1.4989642 [2] Y.Y. Jau et al, arXiv:2006.03728 [3] D. Sarenac et al, PRL 120, 113201 (2018); DOI: 10.1103/PhysRevLett.120.113201 [4] A.J. Brooks et al, Materials and Design 140 (2018) 420--430; DOI: 10.1016/j.matdes.2017.12.001