A new measure of the free life of neutrons reaches a world record precision

Incorporated in all aspects of daily life, neutron is a fundamental particle of nature. Now, a research collaboration led by LOS Alamos National Laboratory has improved the precision of free life measures to neutron life. The results of the team highlight the success of the design of the UCNTAU experience and preview the efficiency of new techniques and approaches that the team incorporates into the next generation of the experience.

“The precise lifespan of free neutrons is at the center of physics issues still disputed,” said Steven Clayton, physicist for Los Alamos. “Understanding the life of neutrons can be used to test the nature of the weak force, one of the fundamental forces of the universe, and can also help seek physics beyond the standard model.

“Our results here validate the experimental approach to the UCNTAU and open the way to design improvements that will further improve our understanding of involved physics.”

The new analysis of the team, published in Physical review CIntegrates three more years of data collection from the experience of the ultra -color neutron installation in the Los Alamos Neutron Science Center, with an accuracy reinforced by improvements in the systematic design of experience. The results update the understanding of the life of the neutron at 877.83 seconds, with an uncertainty reduced to less than 0.3 seconds.

The design of the bathtub offers coherent results

The Experimental apparatus of the UCNTAU – UCN means “ultracold neutrons” and the Tau is the symbol of a lifespan of particles – revolts like a magneto -gravitation trap, resembling a bathtub whose concave surface is covered with magnets and open to the tip. A variation of a “bottle” trap, the UCNTAU experience contrasts with the “beam” approach used by certain life experiences for neutrons.

The approaches resulted in various measures of the life of neutrons, with the “puzzle of the life of neutrons” dividing the physical community around the possibility that a defect in one or the other of the experimental approaches can explain the gap.

The UCNTAU bathtub is filled with ultracold neutrons cryogenically so that they can be counted when they interact with a detector lowered in the bathtub. To avoid the loss of neutrons, the magnets on the interior surfaces prevent neutrons from fleeing through the surface and the gravity prevents neutrons from spreading on the walls of high bathtubs.

Neutrons are counted when a zinc-sulfur detector covered with Bor-10 descends into the bathtub; The neutrons are absorbed by the boron-10 coating on the zinc-sulfur detector and excess energy causes the Bore-10 nucleus rupture, with a fragment of ping on zinc-sulfide and a production of detectable and countable light.

To refine the precision, the UCNTAU team has updated the device each year because it has taken data, in particular the improvement in the surveillance of the number of neutrons which are initially loaded in the trap and the precision of counting the surviving neutrons in the trap after being detained for a certain time. The consistency of recent data with the previous results of the team validates the design of the experience. On average the results of the five years of total racing, the team arrived at the new measure of 877.83 seconds. This figure includes an error estimate of less than 0.3 seconds.

“The results represent the most precise measure of the life of neutrons to date,” said Clayton. “Our objectives were to better understand and quantify systematic uncertainties in experience and improve statistical accuracy for life. With this level of precision, we have taken the current design as far as possible.”

UCNTAU + represents the next generation of experiences

For its next data series, the research team has turned their attention to the considerable increase in the capacity of the experimental apparatus – an iteration of the experience that the team calls “UCNTAU +”. The team changes the trap filling method to increase the density of ultracold neutrons by a factor between 5 and 10 while improving the detector system to reduce the greatest systematic uncertainty of a factor of 10 – to a global uncertainty target of 0.1 seconds.

The team guarantees counting accuracy by developing a new UCN detector with a scintiller based on a perovskite material which can be made to provide a similar light output but without the long fluorescence path found with the current scintillator.

In the center of the effort to provide more neutrons density is a newly installed “elevator” which loads the neutrons in the bathtub, swinging forward and down in the trap. Made from copper and teflon, useful for reflecting neutrons to avoid leaks through metal, the elevator can provide a greater neutrons load in the trap. The trap was designed and manufactured in collaboration with the University of Illinois Champaign-Urbana.

“The elevator itself was difficult to conceive and execute because it must form a seal by backing, and we needed gaps to be reasonable,” said Singh, a postdoctoral researcher of Los Alamos in the UCNTAU team. “The transport of the elevator was done before but not on this scale, and not with this geometry, where the elevator must move other than directly. The implementation of this technique was an exciting challenge.”

The team hopes to bring UCNTAU + online this summer to start taking data.