Vanishing Neutrons
Why neutrons becoming antimatter is fascinating, and how we can see it for ourselves.
Why do we exist? When we look out round the universe we can see stars and galaxies in every direction. Why is this all here? this can be explained via a phenomenon known as CP violation
To explain this, we need a mechanism that violates Baryon number—a rule in particle physics that says matter and antimatter must balance. While most searches focus on protons decaying, there is a more exotic alternative: what if a neutron could spontaneously turn into an antineutron ()?
The Magnetic Dampening
If this transition happens, it is incredibly rare. Theoretical models suggest a free neutron would need over seconds to flip. But here is the catch: we don't live in a vacuum. We live on Earth, surrounded by a magnetic field.
Because neutrons and antineutrons have opposite magnetic moments, an external magnetic field forces their energy levels to split. This Zeeman splitting () completely disrupts the delicate quantum superposition required for the particle to oscillate.
The Mathematical Collapse
Because the interaction mass () is infinitesimally small, any environmental energy split () crushes the probability amplitude to near zero.
Our Monte Carlo simulations using Geant4 confirm this mathematically. If a beam of cold neutrons flies down a 50-meter tube, even a localised magnetic "hot spot" of 10 nanotesla is enough to quench the signal entirely.
This is exactly why experiments like HIBEAM at the European Spallation Source require multi-layer Mu-metal shielding. We aren't just fighting background noise; we are fighting the environment's tendency to force the universe to "choose" a state. By creating the most magnetically pristine vacuum on Earth, we might just catch matter looking in the mirror.