Last updated April 5, 2018 at 12:12 pm
Anti-matter may be one of the most elusive materials, but scientists at CERN have made the most precise measurements of it yet.
Physicists from CERN have made the most precise measurements of antimatter yet, taking another step in the development of uber-sensitive tests of the elusive material.
The existence of antimatter was first predicted in modern theory in 1928, when British physicist Paul Dirac reasoned that every particle has a corresponding antiparticle — exactly the same but with the opposite charge. Antimatter’s existence was confirmed in 1932 with the discovery of the positron (a positively charged electron) , but puzzles still remain.
The Big Bang should have created an equal amount of matter and antimatter, so it has long mystified physicists why today’s Universe consists almost completely of matter. Studying antimatter and understanding its properties are key to untangling this complex question — but unhelpfully, antimatter is difficult to produce and contain. Matter and antimatter annihilate each other when they meet, so to be studied antimatter must be synthesised and then trapped in a vacuum away from normal matter.
Measuring elusive anti-particles
CERN’s ALPHA experiment in Switzerland has been striving for many years to make high-precision measurements of antimatter. They focus on antihydrogen because it’s the simplest form of antimatter, and hydrogen has played an indispensable role in the evolution of the Universe. The experiment aims to discover even a tiny difference between matter and antimatter, which may help explain why matter dominates the cosmos.
In 2017, the team observed antihydrogen using a technique called spectroscopy: a laser was used to excite the atoms to higher energy levels, and as the atom drops back down to ground level energy, the team could detect the specific wavelengths of light that the atoms emitted. Specifically, the researchers observed the transition between the ground state and the excited state 2S.
Now the same team, led by Jeffrey Hangst from Aarhus University in Denmark, has delved even further, studying 15,000 antihydrogen atoms that they carefully trapped using magnetic fields. Over ten weeks, the team collected precise measurements of the resonance frequency of the atomic transition first reported in 2017.
The measurements — which have a precision of two parts in a trillion, a thousand times more accurate than the 2017 experiment — were then compared to hydrogen. Turns out, the resonance frequency for the equivalent transitions in hydrogen and antihydrogen match.
This result is simultaneously exciting and disappointing. On one hand, it means the team haven’t yet found the sought-after difference between antimatter and matter. On the other hand, it confirms that the techniques used to trap and study antimatter are robust and reliable, paving the way for ever-more-precise measurements of antimatter — not just of antihydrogen but of other atoms too.
If these increasingly precise measurements eventually find even a single difference between antimatter and matter, it will affect our fundamental understanding of the universe.
The paper is published in journal Nature.
