Scientists Uncover New Physics in the Search for Dark Matter

No, dark matter is still a mystery to science. But while looking for it, scientists from MSU contributed to the discovery of new physics.

Around three years ago, Wolfgang "Wolfi" Mittig and Yassid Ayyad started looking for dark matter, also known as the missing mass of the universe, in the center of an atom.

The scientists did not find dark matter throughout their search, but they did find something that had never been seen before and defied explanation. At least provide a justification that could be accepted by all.

Mittig, a Hannah Distinguished Professor in the Department of Physics and Astronomy at Michigan State University and a faculty member at the Facility for Rare Isotope Beams, or FRIB, described the investigation as "something akin to a detective story."

He claimed, "We began by seeking for dark matter and we didn't find it. Instead, we discovered other phenomena that have been difficult to explain by theory.

The team got back to work, running more experiments and gathering more data, in order to make their discovery make sense. At the National Superconducting Cyclotron Laboratory, or NSCL, of Michigan State University, Mittig, Ayyad, and their associates supported their claim.

While working at NSCL, the researchers found a new path to their unexpected goal, which they published about in the journal Physical Review Letters. They also revealed fascinating physics at play in the world of subatomic particles' ultra-small quantum particles.                                                                                       

In particular, the researchers demonstrated that even when an atom's nucleus, or center, is overloaded with neutrons, it can still find a way to a more stable shape by spitting out a proton.

One of the most well-known and least understood phenomena in the universe is dark matter. The existence of greater mass than we can detect from the motions of galaxies and stars has long been recognized by scientists.

For gravity to confine celestial objects to their trajectories, six times as much unseen mass as conventional matter that we can see, measure, and classify is needed. Although scientists are confident that dark matter exists, they have not yet identified it or developed a direct detection method.

Ayyad, a nuclear physics researcher at the Galician Institute of High Energy Physics, or IGFAE, at the University of Santiago de Compostela in Spain, stated that "finding dark matter is one of the major goals of physics."

In an effort to shed light on what precisely dark matter is, scientists have run around 100 experiments, Mittig said.

After 20, 30, or 40 years of investigation, "none of them has succeeded," he declared.

Ayyad, a former detector systems physicist at NSCL, said: "But there was a thought, a very speculative idea, that you could observe dark matter with a very special type of nucleus."

This notion was based on what is referred to as a "dark decline." It proposed that some unstable, naturally disintegrating nuclei might release dark matter when they broke apart.

Knowing the odds were against them, Ayyad, Mittig, and his colleagues created an experiment that could search for a dark deterioration. The risk, however, wasn't as great as it would have seemed because investigating unusual decays also helps scientists learn more about the laws and structures governing the nuclear and quantum worlds.

There was a considerable probability that the researchers would find anything novel. What exactly would that be was the question.

Many people could see a nucleus as a lumpy ball consisting of protons and neutrons, according to Ayyad. However, some nuclei can adopt unusual forms, such as halo nuclei.

A typical example of a halo nuclei is beryllium-11. It is an isotope of the beryllium element, which has a nucleus composed of four protons and seven neutrons. It maintains a tightly packed center cluster of 10 of those 11 nuclear particles. However, one neutron floats far from the core, loosely connected to the remainder of the nucleus, similar to how the moon circles the Earth, according to Ayyad.

Additionally unstable is beryllium-11. It decays by a process known as beta disintegrate after a lifetime of approximately 13.8 seconds. A proton is created when one of its neutrons releases an electron. This changes the nucleus into boron-11, a stable isotope of boron with five protons and six neutrons.

However, in accordance with that speculative idea, if the neutron that decays is the one in the halo, beryllium-11 might take a completely different path and experience a dark decay.

At TRIUMF, Canada's national particle accelerator facility, the researchers began an experiment in 2019 to search for that speculative decay. A decay with an unexpectedly high probability was also discovered, but it wasn't a dark decay.

Despite not following the expected decay path to boron, it appeared as though the beryllium-11's loosely bound neutron was ejecting an electron in accordance with standard beta decay.

The scientists proposed that if a state in boron-11 existed as a gateway to another decay, to beryllium-10 and a proton, the high probability of the decay might be explained. That meant that the nucleus had once more changed to beryllium for those keeping score. Instead of seven neutrons, it now only had six.

According to Ayyad, "the halo nucleus is the only reason this occurs." It's an extremely unusual form of radioactivity. Actually, it was the first instance of a neutron-rich nucleus directly exhibiting proton radioactivity.

The team's 2019 report, however, was met with a fair dose of both since science invites examination and skepticism. The majority of theoretical models didn't seem to fit with the "doorway" condition of boron-11. Without a firm theory to explain what the team observed, several experts interpreted the team's data in different ways and proposed alternative hypotheses.

Even though the discussions were and are helpful, Mittig and Ayyad realized they would need to produce more proof to back up their findings and hypotheses. They would need to create fresh experiments.

In their 2019 experiment, the team used TRIUMF to produce a beam of beryllium-11 nuclei, which they then guided into a detection room where they detected various potential decay pathways. That included the process that produced beryllium-10, beta decay to proton emission.

The team's plan for the new tests, which were conducted in August 2021, was to effectively perform the time-reversed reaction. To start, the scientists would use beryllium-10 nuclei and then add a proton.

Beryllium-10, which has a half-life of 1.4 million years, was produced by collaborators in Switzerland and provided to NSCL so that it could employ new reaccelerator technology to make radioactive beams. The method allowed scientists to perform a highly accurate measurement by evaporating the beryllium and injecting it into an accelerator.

The same excited state that the researchers thought they had discovered three years earlier was entered when beryllium-10 absorbed a proton of the proper energy. Even worse, it would spit the proton back out, leaving a trace that the procedure had taken place.

The good news wasn't limited to that. Unbeknownst to the investigators, another method of investigating the 2019 outcome had been developed by a separate team of scientists at Florida State University. Ayyad was inspired by what he witnessed when he happened to attend a virtual conference when the Florida State team presented its preliminary results.

He said, "I grabbed a screenshot of the Zoom meeting and forwarded it to Wolfi right away. Then we got in touch with the Florida State team and devised a plan for mutual support.

Both scientific publications are now included in the same issue of Physical Review Letters thanks to communication between the two teams as they created their studies. And the community is already talking about the fresh outcomes.

The project is receiving a lot of interest. In a few weeks, Wolfi will travel to Spain to discuss this, Ayyad stated.

The work of the researchers may offer a fresh case study for so-called open quantum systems, which contributes to some of the enthusiasm. Although the word seems daunting, the idea is similar to the proverb that says "nothing exists in a vacuum."

Atoms, molecules, and a vast array of other exceedingly small elements of nature can now be understood via the lens of quantum physics. Almost all areas of physical research, such as energy, chemistry, and materials science, have advanced as a result of this understanding.                                                           

However, a large portion of that architecture was created with simplified scenarios in mind. The ultra-small system of interest would be in some way cut off from the vast amount of input the environment provides. Physicists are straying from idealized settings and exploring the complexity of reality by investigating open quantum systems.

Open quantum systems are literally everywhere, but it can be difficult to identify one that is tractable enough to provide useful information, particularly when it comes to nuclear issues. In their loosely bound nuclei, Mittig and Ayyad sensed potential, and they were aware that NSCL and now FRIB could aid in its development.

The work of Mittig and Ayyad, the first published demonstration of the stand-alone reaccelerator technology, was hosted by NSCL, a National Science Foundation user facility that has long served the scientific community. The work can be continued in the future at FRIB, a US Department of Energy Office of Science user facility that formally opened on May 2, 2022.

Open quantum systems are a common occurrence, but they represent a novel concept in nuclear physics, according to Ayyad. And FRIB is home to the majority of theorists who are working on this.

But we are still in the early stages of this detective novel. To fully understand what they are witnessing, researchers still need more information and proof to conclude the case. That indicates that Ayyad and Mittig are still conducting their best investigation.

Mittig declared, "We're moving forward and conducting new trials. The overarching message of this is how crucial it is to conduct effective experiments and conduct thorough analyses.

The National Science Foundation provided funding for NSCL, a national user facility that supported the goals of the Physics Division's Nuclear Physics program.

By MICHIGAN STATE UNIVERSITY