Testing the Viability of Muon Accelerators

Muons are elementary particles that have a similar charge as that of an electron but are 200 times heavier than electrons.

As an elementary particle, its properties are described by the Standard Model of Particle Physics, a theoretical model that describes the interaction and nature of all subatomic particles. However, the experimentally observed value of the anomalous magnetic moment of muons has not matched the theoretical values predicted by the Standard Model, which indicates New Physics beyond the Standard Model.

To improve the accuracy of the experimental measurements, researchers in Japan are planning to reduce the beam-related uncertainties in the measurements by using a low-emittance muon beam where thermal muons are generated, accelerated, and then stored as ultracold muons.

Now, in a new study published in Progress of Theoretical and Experimental Physics, researchers from the High Energy Accelerator Research Organization in Japan have tested the viability of the proposed muon accelerator for the first time.

For the test, negative muonium ions, which are muons coupled to two electrons, were initially generated by striking an Aluminum film with positive muons. A radio-frequency quadrupole was then used to accelerate and bunch the muonium ions to 89 kilo electron volts.

The accelerated muonium ions were detected by a micro-channel plate detector which measured the flight time of the accelerated muonium ions.

With the accelerator in operation, the measured flight time was observed to peak around 830 nanoseconds indicating that the radio-frequency quadrupole was successful at accelerating muonium ions to the speed of light.

The findings of this study show that muon accelerators can be realized and used to measure muon anomalous magnetic moment. By miniaturizing the accelerator, it will be possible to apply it to transmission imaging, which is currently realized with cosmic-ray muons.