Many theories beyond the Standard Model postulate short-range modifications to gravity which produce deviations of Newton's gravitational potential from a strict 1/r dependence. It is common to analyze experiments searching for these modifications using a potential of the formThe best present constraints on α for λ < 100 nm come from neutron scattering and often employ comparisons of different measurements of the coherent neutron scattering amplitudes b. We analyze the internal consistency of existing data from two different types of measurements of low energy neutron scattering amplitudes: neutron interferometry, which involves momentum transfers q 2 = 0, and neutron gravity reflectometry, which involves momentum transfers q 2 = 8mVopt where m is the neutron mass and Vopt is the neutron optical potential of the medium. We show that the fractional difference ∆b |b| averaged over the 7 elements where high precision data exists on the same material from both measurement methods is [2.2 ± 1.4] × 10 −4 . We also show that ∆b |b| for this data is insensitive both to exotic Yukawa interactions and also to the electromagnetic neutron-atom interactions proportional to the neutron-electron scattering length bne and the neutron polarizability scattering amplitude b pol . This result will be useful in any future global analyses of neutron scattering data to determine bne and bound α and λ. We also discuss how various neutron interferometric and scattering techniques with cold and ultracold neutrons can be used to improve the precision of b measurements and make some specific proposals.

We describe a modular apparatus for use in parity-violation measurements in epithermal neutron-nucleus resonances with high instantaneous neutron fluxes at the Manuel Lujan Jr. Neutron Scattering Center at Los Alamos National Laboratory. This apparatus is designed to conduct high-precision measurements of the parity-odd transmission asymmetry of longitudinally polarized neutrons through targets containing nuclei with p-wave neutronnucleus resonances in the 0.1-10 eV energy regime and to accommodate a future search for time reversal violation in polarized neutron transmission through polarized nuclear targets. The apparatus consists of an adjustable neutron and gamma collimation system, a 3 He-4 He ion chamber neutron flux monitor, two identical cryostats for target cooling, an adiabatic eV-neutron spin flipper, a near-unit efficiency 6 Li-7 Li scintillation detector operated in current mode, a flexible CAEN data acquisition system, and a neutron spin filter based on spin-exchange optical pumping of 3 He gas. We describe the features of the apparatus design devoted to the suppression of systematic errors in parity-odd asymmetry measurements. We describe the configuration of the apparatus used to conduct a precision measurement of parity violation at the 0.7 eV p-wave resonance in 139 La which employs two identical 139 La targets, one to polarize the beam on the p-wave resonance using the weak interaction and one to analyze the polarization.

We evaluate the reflectivity of neutron mirrors composed of certain heavy nuclei which possess strong neutron-nucleus resonances in the eV energy range. We show that the reflectivity of such a mirror for some nuclei can in principle be high enough near energies corresponding to compound neutron-nucleus resonances to be of interest for certain scientific applications in non-destructive evaluation of subsurface material composition and in the theory of neutron optics beyond the kinematic limit.