Speaker
Description
Neutron beams can be used to perform high precision probes for a wide variety of new forces or interactions not a part of the standard model of particle physics. The neutron's lack of a net charge, its penetrating power into material targets and the availability of intense beams at neutron scattering facilities provide a number of advantages for neutron beam experiments. In particular, they provide the most stringent probes for new spin-independent and spin-dependent interactions over several different distance scales, and new experiments are being proposed which can provide unique sensitivity to CP-violating and B-violating interactions. A brief overview of some of these on-going and proposed experiments is provided, before focusing on a specific example: pendellosung measurements with thermal and cold neutron beams.
Pendellosung is the result of dynamical diffraction, involving the reflected and transmitted beams in a perfect crystal when the neutron beam is tuned to a Bragg condition. In this case, the eigenstates of the neutron beam are admixtures of reflected and transmitted beams, and the neutron state undergoes oscillations. These oscillations can be detected by monitoring the intensity of beams transmitted through the crystal, and are exquisitely sensitive to the atomic potential in the unit cell of the crystal. Recent experiments using perfect Si crystals were conducted at the National Institute of Standards and Technology (through an international collaboration between U.S. and Japanese groups) which provided the highest precision measurements for structure factors for 3 Bragg conditions <111>, <220>, and <400>. These measurements provided what are currently the strongest constraints on Yukawa-like extensions of gravity as well as a new determination of the "charge-radius" of the neutron. We outline the progress since that time using pulsed neutron beams at the SNS and prospects for improvements in the near future using pendellosung on Si and other crystalline materials.
