Unless you’re involved in the study of particle physics or a similar field, there’s a good chance you might never have heard of a muon.
Similar to electrons, but around 200 times heavier, muons interact only weakly with matter, allowing them to be used like X-rays but for large and dense structures like geological features, bridges, and dams.
The muon's larger mass also makes them sensitive and useful for understanding fundamental physics. However, one of the challenges for scientists has always been that despite their apparent benefits to science – and even society more broadly – muons only have a half-life of around one microsecond.
Now researchers at the University of Plymouth have suggested a means of overcoming that, using intense laser pulses to reduce the rate of decay and at least double the muon’s lifetime.
They believe their theory will eventually benefit those working in fields that employ muons, such as geology, material science and particle physics.
However, it could also help work to develop the next generation of scientific facilities that will ultimately succeed the Large Hadron Collider, with muons – rather than electrons – being suggested as a more sensitive particle species.
The theory, outlined in the journal Physical Review Letters, was developed by Associate Professor of Theoretical Physics Dr Ben King and Postdoctoral Research Fellow Dr Di Liu, both from the University’s School of Engineering, Computing and Mathematics.
Dr King, who teaches across the University’s Mathematics, Theoretical Physics and Data Science courses, said: “I've always believed high power lasers have great potential to study fundamental physics. Although it was long thought to be effectively impossible to modify the natural instability of muons, we decided to revisit the question in the light of developments in experiment and theory. Ultimately, we were able to find a new route to influencing the muon's lifetime that circumvented the established difficulties.”
Muons are created through particle collisions that occur within scientific facilities and when high energy particles from space (cosmic rays) collide with molecules in Earth's upper atmosphere. It has also been recently demonstrated that shining a laser on a thin target can generate various exotic particle types, one of them being muons.
However, no sooner are muons formed than they begin to decay so – supported through funding from the Leverhulme Trust – Dr King and Dr Liu undertook a theory-based project asking whether the decay properties of a muon can be changed using a laser.
Their theory uses a principle of quantum mechanics, known as the quantum interference. It works on the basis that different routes to a particular outcome – in this case, the decay of a muon – act like waves and when added together can reinforce each other or cancel each other out.
This wave-like behaviour is predicted to be visible in experiments in the position that the muon decay products are measured.
Dr King added: “This is a process that can be investigated with technology we have at our disposal today. We are working with others in the field to overcome any remaining hurdles before experiments can be performed, such as excluding background processes and ensuring a good overlap of the muons with the laser. However, our method suggests a general way to influence the decay of charged particles, even when one might naively expect the required electromagnetic strength to be much higher than anything we could ever hope to achieve in the lab.”
Physical Review Letters
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Vacuum Muon Decay and Interaction with Laser Pulses
17-Dec-2025