Physicists are always searching for new theories to improve our understanding of the universe and resolve big unanswered questions.
When researchers compared the two numbers, they found a tiny but significant difference, indicating a mismatch between theory and experiment.
Antimatter vs supercomputers It was not possible to compute this contribution in the same way as the others, so we needed a different approach.
However, now we had a new tension: between our simulation and the electron–positron results which had withstood 20 years of scrutiny.
Physicists around the globe have studied this question extensively, and one exciting suggestion is a hypothetical particle called a “dark photon”.
In order to better understand the universe and address important unresolved issues, physicists are constantly looking for new theories.
However, there’s an issue. When you don’t know what undiscovered forces or particles look like, how do you go about finding them?
Think about dark matter. We see evidence of this enigmatic cosmic phenomenon all over the universe, but what could it be composed of? New physics will be required to explain it.
We may now have a better understanding of this new physics and possibly even some hints regarding dark matter thanks to a new experimental result that was published today and the accompanying theoretical calculations.
Get to know the muon.
For the past two decades, a small discrepancy in the muon’s magnetism has been one of the most encouraging indications of new physics. Similar to an electron, but much heavier, is the muon.
When cosmic rays—high-energy particles from space—strike the Earth’s atmosphere, muons are created. Every second, about fifty of these muons travel through your body.
Muons are useful for determining what is inside large structures because they travel through solid objects much more effectively than x-rays. For instance, they have been used to safely enter the Fukushima nuclear reactor after it melted down, investigate magma chambers inside volcanoes to forecast volcanic eruptions, and search for hidden chambers in Egyptian and Mexican pyramids.
A small rift in physics?
In 2006, scientists at the United States’ Brookhaven National Laboratory made an extremely accurate measurement of the muon’s magnetism strength.
About six parts in ten billion was the accuracy of their measurement. This corresponds to ten grams being the mass of a loaded freight train. A theoretical calculation that was equally impressive was compared to this.
A small but significant difference between the two numbers was discovered by researchers, suggesting that theory and experiment were not aligned. Had they at last discovered the novel physics they were seeking?
A better test.
To improve the accuracy of both findings, the international scientific community began a 20-year program to find a conclusive answer.
After being loaded onto a barge, the massive electromagnet from the initial experiment was transported to Chicago via the Mississippi River and the US east coast. It was set up for a totally redesigned experiment at Fermilab.
Researchers declared that experiment was completed just this morning. At 1.5 parts in ten billion, their final result for the muon’s magnetism strength is 4 times more accurate.
and more accurate computations.
Theorists also had to make broad advancements to stay up. In order to make an accurate theoretical prediction, they established the Muon g-2 Theory Initiative, an international team comprising over 100 scientists.
They calculated the more than 10,000 factors that contribute to the muon’s magnetism. They even included the Higgs boson, a particle that was only identified in 2012.
The strong nuclear force, one of the four fundamental forces of the universe, was the final point of contention. It was particularly difficult to determine the strong nuclear force’s largest contribution to the outcome.
Supercomputers and antimatter.
We needed a different method because this contribution could not be calculated in the same way as the others.
The Theory Initiative shifted its focus to collisions between electrons and positrons, which are their antimatter counterparts, in 2020. The missing values we required were obtained from measurements of these electron-positron collisions.
When combined with all the other components, the result was a significant departure from the most recent experimental measurement. The disagreement nearly amounted to announcing the discovery of new physics.
At the same time, I was looking into an alternative strategy. I conducted a supercomputer simulation of this powerful contribution with my colleagues in the Budapest-Marseille-Wuppertal collaboration.
The conflict between theory and experiment was resolved by our findings. Nevertheless, a new conflict arose between our simulation and the electron-positron results that had withstood examination for two decades. What made those results from 20 years ago incorrect?
New physics hints vanish.
Since then, numerous other groups have validated portions of our result, and two other groups have produced complete simulations that concur with ours. Our precision has nearly doubled thanks to a newly redesigned simulation that we have released as a preprint that has not yet undergone peer review or been published in a scientific journal.
These novel simulations were run “blind” to make sure no preconceptions influenced them. Because the simulation data was multiplied by an unidentified number prior to analysis, we were unable to determine what a “good” or “bad” outcome would be.
After that, we had an exciting and nerve-racking meeting. The results of years of work were all revealed at once, and the blinding factor was exposed. Our most recent result, in spite of everything, agrees even more with the experimental measurement of the muon’s magnetism.
But others show up.
In its official prediction, the Muon g-2 Theory Initiative has shifted from using electron-positron data to using simulation results, and the indication of new physics appears to have vanished.
Except … why do the electron–positron data contradict? This question has been thoroughly investigated by physicists worldwide, and one intriguing proposal is a hypothetical particle known as a “dark photon.”.
If the dark photon exists, it could explain not only the discrepancy between the electron-positron experiments and the most recent muon results, but also the relationship between dark matter and ordinary matter.
