Shulou(Shulou.com)05/31 Report--

Physical experiments conducted by the National Institute of Standards and Technology (NIST) have enhanced scientists' understanding of how free neutrons decay into other particles. This work provides the first measurement of the energy spectrum of photons or light particles, which are released in an extensive measurement process called neutron decay. The details of this decay are important because, for example, they help explain the amount of hydrogen and other light atoms observed after the Big Bang.

The results, published in the physical Review KuaiBao (Physical Review Letters), confirm physicists' comprehensive understanding of how particles and forces work together in the universe-an understanding known as the standard model. This work has inspired a new theoretical activity in quantum electrodynamics (QED), a modern theory of how matter interacts with light. The team's approach can also help find new physics outside the standard model.

It is well known that neutrons are one of the three particles that form atoms. Of all atoms, except hydrogen, the most common, neutrons and protons form nuclei together. However, "free" neutrons that are not bound to the nucleus decay in an average of about 15 minutes. Most commonly, neutrons decay into antimatter forms of protons, electrons, photons and neutrinos, an elusive particle with little interaction with matter.

Photons from decay are what the team wants to explore. These photons have a range of possible energies predicted by QED, and QED has been running as a theory for decades. But no one has really studied this aspect of quantitative easing with high precision.

"We didn't expect to see anything unusual," said Jeff Nico, a NIST physicist, but we wanted to test QED's predictions very accurately in an unprecedented way.

Nico, who represents nine research institutions, and his colleagues took measurements at the NIST Neutron Research Center (NCNR). It produces a beam of strong and slow-moving neutrons whose photon emission can be used to accurately measure the neutron lifetime at the same setting in the early stage.

The team measured two aspects of neutron decay: the photon's energy spectrum and its branching ratio, which provides information about the frequency at which photon decay accompanies higher than a certain energy. As a result of this work, their bifurcations are more than twice as accurate as the previous values, and the energy spectrum is measured for the first time.

"everything we found is consistent with the major QED calculations," Nico said. "We match the energy spectrum theory very well and reduce the uncertainty of the branching ratio."

Nico believes that these results provide specific information that theoretical physicists use to further develop QED, thus providing a more detailed description of neutron decay.

Nico says the results can be used as a necessary check of the standard model and verify that the team's experimental method is a way to go beyond it. With better detectors, this method can be used to search for so-called "right-handed" neutrinos, which are not detected in nature and have potential time reversal symmetry violations. this could explain why there is more matter than antimatter in the universe.

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