Particle experiments challenge physical paradigms

Preliminary results from two experiments suggest that there may be something wrong with the fundamental way physicists believe the universe works, a prospect that has caused confusion and excitement in the field of particle physics.

The tiny particles called muons did not behave as expected in two separate long-term experiments in the United States and Europe. The puzzling results – if proven correct – reveal major problems in the norms that physicists use to describe and understand the workings of the universe at the subatomic level.

“We thought we could swim all the time in a sea of ​​background particles that just weren’t immediately discovered,” said scientist Chris Polly, co-director of experiments at the Fermilab lab, at a news conference. “There may be monsters that we hadn’t imagined yet that emerge from the void and interact with our muons, and this gives us a window to see them.”

The articles of association are laid down in the so-called Standard Model that was developed some 50 years ago. Experiments over the decades have claimed time and again that their descriptions of the particles and forces that make up and control the universe were quite accurate. Up to now.

“New particles, new physics may be just outside our research,” said particle physicist Alexey Petrov of Wayne State University. “It’s tempting”.

The U.S. Department of Energy’s Fermilab on Wednesday announced the results of 8.2 billion races along a track outside Chicago that, while not piquing most people’s interest, have thrilled fans. Physics: The magnetic fields of the muons do not seem to be what the Standard Model says they should be. This follows new results published last month by the Large Hadron Collider of the European Center for Nuclear Research (CERN), which found a surprising proportion of the particles after high-speed collisions.

If confirmed, the US results would be the largest find in the strange world of subatomic particles in nearly 10 years since the discovery of the Higgs boson – often referred to as a ‘God particle’ – said Aida El-Khadra of the University of Illinois. , working on theoretical physics in the Fermilab experiment.

The purpose of the experiments, explains theoretical physicist David Kaplan, of Johns Hopkins University, is to separate particles and find out if “something strange is going on,” both with the particles and the apparent empty space between them. .

“The secrets are not only in the business. They are in something that seems to fill all space and time. These are quantum fields, ”noted Kaplan. “We put energy in a vacuum and see what works.”

The two sets of results relate to the strange, ephemeral particle called a muon. The muon is the heavier cousin of the electron orbiting the center of an atom. However, the muon is not part of the atom, it is unstable and normally only exists for two microseconds. After it was discovered in cosmic rays in 1936, it caused so much confusion among scientists that a famous physicist asked, “Who ordered that?”

“From the start, it has made physicists scratch their heads,” said Graziano Venanzoni, an experimental physicist at an Italian national laboratory. Venanzoni is one of the main scientists of the American Fermilab experiment, called Muon g-2.

In the experiment, muons are released along a magnetized track that maintains the particles long enough for researchers to observe them up close. Preliminary results suggest that the magnetic “rotation” of the muons deviates 0.1% from what the Standard Model predicts. The figure may not sound like much, but to particle physicists, it’s huge, more than enough to call into question the current understanding of the phenomenon.

It will take the researchers another year or two to complete the analysis of the results of all laps around the 14-meter course. If the results stay the same, it counts as a great discovery, Venanzoni said.

On the other hand, physicists have conducted proton collisions at the world’s largest particle accelerator at CERN to see what happens next. One of many separate particle collision experiments measures what happens when particles called “beauty quarks” or “background” collide with each other.

The Standard Model predicts that these beauty quark collisions should result in an equal number of electrons and muons. It’s like flipping a coin 1,000 times and getting the same number of heads or coins, said Chris Parkes, head of the beauty quark experiment at the Large Hadron Collider.

But that did not happen.

The researchers examined data from several years and thousands of collisions and found a 15% difference, with significantly more electrons than muons, said Sheldon Stone, a researcher on the experiment at Syracuse University.

No experiment has yet been declared an official discovery, because the results are unlikely to be a statistical oddity. Running the experiments more often – scheduled in both cases – could meet the incredibly strict statistical requirements for physics to consider them a discovery in a year or two, the researchers said.

If the results hold, they could radically change “all calculations” in the world of particle physics, Kaplan said.

“This is not a margin of error. This is something wrong, “he added. That something can be explained by a new particle or force.

Or these results could be errors. In 2011, a strange finding that a particle called neutrino appeared to be traveling faster than light threatened the Standard Model, but it turned out that this was due to an electrical connection problem in the experiment.

“We reviewed all of our cable connections and did what we could to verify our data,” said Stone. “We have the certainty, but you never know.”