Groundbreaking technique may lead to discovery of 'fifth force'

The research was an international collaboration conducted at the National Institute of Standards and Technology (NIST). Dmitry Pushin, a member of the University of Waterloo’s Institute for Quantum Computing and a faculty member in Waterloo’s Department of Physics and Astronomy, was the only Canadian researcher involved in the study. Pushin was interested in producing high-quality quantum sensors out of perfect crystals.

First measurement of a key neutron property in 20 years

Picture of Dmitry Pushin at the National Institute for Standards and Technology (NIST) Centre for Neutron Research (NCNR) in Maryland, United State.

By aiming subatomic particles known as neutrons at silicon crystals and monitoring the outcome with exquisite sensitivity, researchers were able to obtain three extraordinary results: the first measurement of a key neutron property in 20 years using a unique method; the highest-precision measurements of the effects of heat-related vibrations in a silicon crystal; and limits on the strength of a possible 'fifth force' beyond standard physics theories. 

In collaboration with researchers from Japan, the US and Canada, the latest work resulted in a fourfold improvement in precision measurement of the silicon crystal structure factor. 

Pushin, whose research specialises in neutron physics and interferometry, was instrumental in collecting neutron data and chemically etching samples, which led to examining unexplored forces beyond Standard Model.

“This was a multi-year experiment, and we had great results that are technically exciting and opens the door to future technologies,” said Pushin.

Standard Model is an incomplete explanation of nature

The Standard Model is currently the widely accepted theory of how particles and forces interact at the smallest scales. But it’s an incomplete explanation of how nature works, and scientists suspect there is more to the universe than the theory describes.

The Standard Model describes three fundamental forces in nature: electromagnetic, strong and weak nuclear force. Each force operates through the action of 'carrier particles.' For example, the photon is the force carrier for the electromagnetic force. But the Standard Model has yet to incorporate gravity in its description of nature. Furthermore, some experiments and theories suggest the possible presence of a fifth force.

The researchers are already planning more expansive pendellösung measurements using both silicon and germanium. They expect a possible factor of five reduction in their measurement uncertainties, which could produce the most precise measurement of the neutron charge radius to date and further constrain — or discover — a fifth force. They also plan to perform a cryogenic version of the experiment, which would lend insight into how the crystal atoms behave in their so-called “quantum ground state,” which accounts for the fact that quantum objects are never perfectly still, even at temperatures approaching absolute zero.

The study, Pendellösung Interferometry Probes the Neutron Charge Radius, Lattice Dynamics, and Fifth Forces, was published this week in the journal Science.