Physicists Trap Ultracold Neutrons in a Bottle to See How Long They Live

An worldwide group of researchers lately measured the lifetime of a neutron exterior of an atomic nucleus with extraordinary precision. By their measurements, the neutron survived for 14.629 minutes, or 877.75 seconds, give or take a 3rd of a second.

Neutrons usually are not alive. But the particles—integral elements of the nuclei of atoms—do decay, into positively charged protons and different particles. Neutrons exterior of atoms are referred to as free neutrons, and the timing of their decay is an important factor to know for physicists making an attempt to grasp what number of neutrons had been obtainable to kind the primary atomic nuclei within the extraordinarily early universe; totally different numbers of neutrons then would lead to very totally different quantities of the weather we discover within the universe at this time, the weather that gave rise to life.

Scientists have identified for years {that a} lonely neutron will die in a couple of quarter-hour, courting again to the original measurement of a free neutron’s decay in 1951. But the brand new measurement—the results of years of experimentation within the UNCtau equipment on the Los Alamos Neutron Science Center—is probably the most exact but of its form. The group’s outcomes had been published final week in Physical Review Letters.

The paper is “a very impressive result,” mentioned Shannon Hoogerheide, a physicist with the National Institute of Standards and Technology who wasn’t concerned within the new analysis. “The UCNtau team has done a great job of carefully addressing a range of systematic uncertainties in their experiment, and the independent, blinded analyses lend confidence to the result. The result is an important step toward improving tests of the Standard Model.”

The discovering “provides an independent assessment to help settle the neutron lifetime puzzle,” mentioned Brad Filippone, a physicist on the California Institute of Technology and a co-author of the paper, in an institute press release. “When combined with other precision measurements, this result could provide the much-searched-for evidence for the discovery of new physics.”

This isn’t the final phrase in the case of how lengthy a free neutron lives. Hardly. There are literally two long-standing strategies for measuring a neutron’s lifespan. One, the beam technique, seems to be at a beam of neutrons and counts the variety of protons that seem because the neutrons decay. The different, the bottle technique, traps free neutrons in a giant, chilly, magnetized bowl (or bottle) and counts the variety of neutrons that stay.

“The bottle experiment measures the survivors, the beam experiment measures the dead,” Geoff Greene, a physicist on the University of Tennessee and Oak Ridge National Laboratory who was unaffiliated with the latest analysis, told the Department of Energy final 12 months. “The bottle experiment sounds easy but actually is very hard. On the other hand, the beam experiment sounds hard and is hard.”

The beam technique reliably produces outcomes which are about 9 seconds longer than the bottle technique; the discrepancy is giant sufficient that the error bars of the 2 strategies don’t overlap. Physicists don’t know whether or not this mismatch is an indication of latest physics that nobody but understands.

Because the bottle technique measures surviving neutrons, it by definition ignores no matter occurs to the neutrons after they decay. Beam experiments, however, are particularly measuring the decay merchandise (on this case, protons). If new physics had been at play, it might imply the neutrons would decay by another means (what physicists name “channels”) in addition to beta decay, Greene advised Gizmodo in a telephone name, yielding particles in addition to protons that stay hypothetical: axions, darkish matter, WIMPS—take your decide.

“What’s tantalizing about this and has driven people nuts for the last 15 years,” Greene defined, “is that it would predict that bottle lifetime would be lower, because there’s another channel, than the beam lifetime.”

If the reply for the discrepancy had been certainly new physics, beam and bottle experimentalists would solely know after proving many times that their respective experiments had been freed from uncertainty and that there wasn’t some bigger systematic error at play.

We’re a great distance off from such realizations; most physicists aren’t the sort to cry wolf, and if any did assume that this lifespan discrepancy was proof that neutrons might decay by another means, they’d have to ensure it was constantly provable in each different experiment that includes nuclear beta decay.

“If you’re not paranoid, you shouldn’t be doing this kind of work,” Greene mentioned.

For now, physicists preserve plugging away on the error bars on the beam and bottle strategies, making an attempt to determine what the outcomes are telling them. Once the fats is trimmed, the scientists would possibly be capable to decide what else may very well be inflicting the nine-second disparity. The new experiment is probably the most exact measurement but taken with bottle technique, for a few causes.

“Our technique is distinguished from other ‘bottle’ measurements by both being a magnetic neutron trap, and by detecting the neutrons within that trap,” mentioned Daniel Salvat, a physicist at Indiana University Bloomington and a co-author of the brand new research, in an electronic mail. “This result uses a completely new and separate dataset from our previous result, and these data were blinded, so that we couldn’t be swayed towards our previous, less precise result.”

The group’s remaining calculation for the neutron decay was an unweighted common of three separate blinded analyses. “The blinding is an excellent technique,” Greene mentioned, noting that blinding doesn’t assist if there may be some systematic impact like a gap within the bottle, which might permit the group to lose neutrons by one other technique in addition to decay.

“But these are very careful people who work very hard at this. I’ve been observing their work for 20 years and I don’t see an obvious error in what they’ve done,” shelp Greene, who’s a beam scientist, including that “I don’t see an obvious error in what we’ve done.”

Beam experiments have yielded fairly constant outcomes as they’ve gotten extra exact, Greene mentioned. Previous bottle technique measurements of such chilly neutrons yielded slightly longer lifespans, and the magnetogravitational lure utilized by the latest group makes their worth for the neutron’s lifespan somewhat shorter.

It’s considerably counterintuitive that ultracold neutrons are getting used to assist us perceive how lengthy neutrons lasted on the terribly sizzling onset of the universe. In the start, gentle parts fashioned from a primordial soup of superheated particles. This course of, referred to as Big Bang nucleosynthesis, would’ve occurred on totally different timescales, relying on how lengthy free neutrons caught round.

“In the first microseconds of the universe, it was so hot that there were no protons, neutrons, or nuclei, but rather a ‘quark soup,’” Salvat mentioned. “Shortly thereafter, the quarks condensed into the droplets that we know as protons and neutrons.”

“After a few seconds, the universe started cooling off enough that the protons and neutrons could stick together, forming the light elements hydrogen, helium, and lithium,” he defined. “If the lifetime of the neutron were very short, all the neutrons would quickly become protons, and we’d only end up with hydrogen in the early universe. That’s not what we observe—the neutrons last more like 15 minutes.”

Besides the tempo of the early universe’s growth, the lifetime of neutrons has implications for physicists probing dark matter, solar fusion, and the Standard Model of physics. But with a view to grasp all of these issues, first researchers want to determine why these neutrons appear to be decaying at totally different occasions.