Researchers hope that muons will spill the beans on the Standard Model of particle physics by studying muonium. The most intense beam of muons in the world is used to make muonium. The research is in a journal.
The muon is a heavy cousin of the electron. It could be its rogue relation. The muon has been bamboozling scientists since its discovery triggered the words "who ordered that".
The muon's most famous mistake is to wobble too much in a magnetic field. The muon caused trouble when it was used to measure the radius of the proton, as it gave rise to a wildly different value than the previous measurement.
The muon's surprising behavior makes it a likely candidate to reveal new physics beyond the standard model.
The muon has an exotic atom known as muonium. Hydrogen is similar to muonium but simpler. The positive muon of muonium does not have a substructure. It gives a very clean model system from which to sort these problems out by obtaining extremely precise values of fundamental constants.
Because we can measure muonium's properties so precisely, we can try to detect deviations from the standard model. "If we see this, we can then infer which of the theories that go beyond the Standard Model are viable or not," says Paolo Crivelli, the leader of the study supported by a European Research Council Consolidator grant.
This can only be achieved in one place in the world.
It is important to have an intense beam of muonium particles in order to make these measurements very precise. It is not easy to make lots of muonium. There is a place in the world where positive muons can be found at low energy.
Slow muons are needed to make muonium efficient. They are going at 25% of the speed of light when they are first produced. We need to slow them down so we don't lose them. We have mastered this art. The world's most intense source of low energy muons is located here. Thomas Prokscha is the head of the Low Energy Muons group at PSI.
Slow muons pass through a thin foil target to form muonium. The team is waiting to probe their properties using microwaves and lasers.
Change in energy levels is the key.
Researchers are able to study muonium's energy levels in detail. The teams were able to measure for the first time a transition between certain energy sub levels. The transition can be modeled very cleanly. The Lamb shift is an important quantity that can be measured using the ability to now measure it.
The Lamb shift is a small change in hydrogen energy levels compared to where they should be. The shift was explained by the advent of quantum physics. In hydrogen, protons possess substructure. The Lamb shift could be used to test the theory.
There's more to come. The muon is not as heavy as the protons. The effects of the nuclear mass are enhanced by this. It is possible to detect these values in hydrogen and use them to test theories about the muon g-2 anomalies.
The scales are being put on the muon.
The team have a bigger goal in mind, and that is to weigh the muon. They will measure a different transition in muonium and it will be one thousand times better than before.
Efforts to reduce uncertainty even further for muon g-2 will be supported by an ultra- high precision value of the muon mass. As experimental precision improves, we need an improved value of the muon mass as an input for the calculations.
A new value of the Rydberg constant could be created by the measurement. It's possible that this could explain the discrepancies between the measurement and the puzzle.
TheIMPACT project is poised to fly with muonium.
The main limitation for such experiments is that they can't produce enough muonium to reduce statistical errors.
"With the high intensity muon beams planned for the IMPACT project, we could potentially go a factor of one hundred higher in precision, and this would be very interesting for the standard model," says Prokscha.
There is a measurement of the transition frequency from 2S1/2 to 2P1/2. The DOI is 10.1038/s41467.
Journal information: Nature Communications
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