Based on the laws of physics, symmetry is a fundamental feature of the cosmos. And yet, when we observe the universe, we see phenomena that defy symmetry – their mechanisms beyond our current models of physics.
A peculiar theory that attempts to fix one of the broken symmetries of the universe calls for the presence of mirror matter. Mirror particles interact with themselves like ordinary particles, but they only very weakly interact with regular particles. Their alleged properties mean they fit well as a candidate for dark matter, which only weakly interacts with the ordinary matter that makes up us, planets, and stars.
But how can we test if this mirror matter exists? Well, New Scientist has written an article on two fantastic experiments: one in Switzerland led by Professor Klaus Kirch and one led by Dr Leah Broussard that will soon take place at Oak Ridge National Laboratory. They are both investigating the existence of mirror neutrons.
Neutrons are one of the particles at the center of atoms. If a neutron is not in an atom but moving freely, it will decay into a proton and an electron (the beta decay). But depending on how this decay is measured, researchers get two different values for the average life of a free neutron. It is either 14 minutes and 39 seconds or 14 minutes and 48 seconds. These estimates are based on the bottle experiment, where a weak magnetic field is used to herd neutrons into a bottle trap, and the neutron beam experiment, where they are instead shot at a detector.
The 9-second difference is attributed, by some, to the mirror neutron. The reasoning is this: the bottle trap counts how many neutrons are left. In the neutron beam, researchers instead count the number of protons that come out. If neutrons are able to transform into a mirror version between emission and detection, then suddenly the proton count will be skewed, leading to the difference. This ability to oscillate into a mirror version might be even more likely in the presence of electromagnetic fields.
Kirch’s experiment looked at exactly that. In a neutron trap, they had varying magnetic fields to see if they could observe changes in the number of particles. The data has been collected and is now being analyzed. Broussard’s experiment will test this oscillation. A neutron beam will be shot at a target that neutrons cannot possibly penetrate. If the neutrons oscillate, some might be able to cross the barrier and be detected on the other side.
Broussard’s interest in neutrons goes beyond the possibility of them being an excellent testing ground for the mirror matter hypothesis. Neutrons might help test the limits of the current model of physics and find out why matter is so much more abundant than antimatter.
“Because we have the Standard Model of particle physics, we can predict very precisely what we expect to happen,” Broussard said in a recent article about her research. “We have a great test of how well we understand the laws of nature. The neutron is the simplest type of [particle] that can undergo radioactive beta decay. That makes it a great system to use to understand this process with excellent sensitivity.”
New insights on mirror matter and/or dark matter might just be a short time away.