Nav: Home

Microscopic universe provides insight into life and death of a neutron

May 30, 2018

A neutron "lives" for almost 15 minutes before it decays. The elementary particles remain stable as long as they are in the atomic nuclei. In isolation, however, they decay after just under 15 minutes into other particles - protons, electrons, and antineutrinos. To determine the lifetime of the neutrons, scientists observe either the emergence of these decay products or the disappearance of the neutrons. However, these two varying experiments deliver different results. The deviation is less than nine seconds. This might not appear to be much, but the conflicts between the experimental measurements could answer key questions about a new physics beyond the known particles and processes in the universe.

For the first time, an international team of scientists used supercomputers to calculate a quantity that is crucial for understanding the lifetime of neutrons: the axial coupling constant of the weak interaction, or gA for short. "It determines the force with which the particles are bound together in the atomic nucleus as well as the radioactive decay rate of the neutron," explains Evan Berkowitz from the Nuclear Physics Institute (IKP). "We were able to calculate the coupling constant with unprecedented precision and our method is paving the way towards further improvements that may explain the experimental discrepancy in the lifetime of neutrons."

Space and time on a lattice

For their calculation, the researchers turned to a key feature of the standard model of particle physics: quantum chromodynamics (QCD). This theory describes how quarks and gluons - the building blocks for nuclear particles such as protons and neutrons - interact with each other. These interactions determine the mass of the nuclear particles, the strength of their coupling, and, therefore, the value of the coupling constants.

However, QCD calculations are extremely complex. For their calculations, the researchers therefore used a numerical simulation known as lattice QCD. "In this simulation, space and time are represented by points on a lattice," explains Berkowitz. "Through this construction, a calculation of the relations between the elementary particles is fundamentally possible - but only with the aid of powerful supercomputers." The scientists used the Titan supercomputer at the Oak Ridge National Laboratory in Tennessee for their simulations.

Microscopic universe

The coupling constant, which previously could only be derived from neutron decay experiments, was thus determined directly from the standard model for the first time. To this end, the researchers created a simulation of a microscopic part of the universe measuring just a few neutrons wide - much smaller than the smallest atom. The model universe contains a single neutron in the middle of a "sea" of gluons and pairs of quarks and their antiparticles, antiquarks. In this microcosm, the scientists simulated the decay of a neutron to predict what happens in nature.

Berkowitz explains that this allows two results for gA from completely independent sources - those from the neutron decay experiments and those using the standard model - to be compared with each other for the first time. "Even the smallest deviations between the values could lead to new discoveries related to dark matter, the asymmetry between matter and antimatter, and other fundamental questions concerning the nature of the universe."

A new era

"Through our simulation, we were also able to show that the lattice QCD approach can be applied to basic research on the physics of atomic nuclei," explains Berkowitz. The methods have so far mainly been used for elementary particle physics, i.e. the physics of quarks and gluons , and of short-lived particles found in collider experiments. "These calculations ring in a new era. We can now determine parameters of nuclear physics with greater precision without having to resort to experimental measurement data or phenomenological models."

Forschungszentrum Juelich

Related Physics Articles:

Diamonds coupled using quantum physics
Researchers at TU Wien have succeeded in coupling the specific defects in two such diamonds with one another.
The physics of wealth inequality
A Duke engineering professor has proposed an explanation for why the income disparity in America between the rich and poor continues to grow.
Physics can predict wealth inequality
The 2016 election year highlighted the growing problem of wealth inequality and finding ways to help the people who are falling behind.
Physics: Toward a practical nuclear pendulum
Researchers from Ludwig-Maximilians-Universitaet (LMU) Munich have, for the first time, measured the lifetime of an excited state in the nucleus of an unstable element.
Flowers use physics to attract pollinators
A new review indicates that flowers may be able to manipulate the laws of physics, by playing with light, using mechanical tricks, and harnessing electrostatic forces to attract pollinators.
More Physics News and Physics Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Teaching For Better Humans
More than test scores or good grades — what do kids need to prepare them for the future? This hour, guest host Manoush Zomorodi and TED speakers explore how to help children grow into better humans, in and out of the classroom. Guests include educators Olympia Della Flora and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...