Studying antimatter and its properties does more than just provide cool ideas to science fiction writers, it could also help explain why the universe is made almost exclusively of matter and not the other way around. So far, however, we have come home empty-handed.
Now, scientists have measured the magnetic moment of the antiproton and discovered that it’s extremely close to the magnetic dipole of the proton, with six times more precision than ever before. The result, published in Nature Communications, is an incredible breakthrough in accuracy, but will disappoint those who were hoping for cracks in the Standard Model of particle physics.
“We see a deep contradiction between the Standard Model of particle physics, under which the proton and antiproton are identical mirror images of one another, and the fact that on cosmological scales, there is an enormous gap between the amount of matter and antimatter in the universe,” co-author Stefan Ulmer, from RIKEN in Japan, said in a statement.
The Standard Model clearly shows a symmetry between matter and antimatter, called CPT. CPT stands for Charge, Parity and Time Reversal and it’s an exact symmetry of nature at the most fundamental level. As matter and antimatter must have a difference somewhere, physicists are hoping to catch antiprotons breaking the CPT symmetry.
“Our experiment has shown, based on a measurement six times more precise than any done before, that the Standard Model holds up, and that there seems in fact to be no difference in the proton/antiproton magnetic moments at the achieved measurement uncertainty," continued Ulmer. "We did not find any evidence for CPT violation."
The team has achieved a precision of 0.8 parts per million by using antiprotons generated at CERN and putting them in a Penning Trap, an extremely powerful magnetic machine. The antiprotons were cooled to almost absolute zero and then their magnetic moment (the quantity of torque experienced once in the magnetic field) was measured.
While the proton and antiproton values are in very good agreement, the team will continue to pursue this avenue to test if the violation is simply hidden below what we can currently see. They plan to use a double Penning Trap, which should make the measurement 1,000 times more precise. They were able to do it for protons already, and although antiprotons are a lot more challenging, they believe that it can be done and will push our knowledge of antimatter forward.