Physicists Made the Most Precise Measurement Ever of a Single Particle


By trapping a single electron in an isolated chamber cooled to near absolute zero, physicists were able to measure the particle's magnetic moment - a key quantum property - at a precision of 1.3 parts in 10 trillion. 


A new assessment of the electron is the most precise measurement of a particle ever taken, at a precision of 1.3 parts in 10 trillion, and could tell us about new physics happening at the smallest scales. 


The electron’s magnetic moment is a quantum property related to magnetism and is predicted by the standard model, our current understanding of how the basic building blocks of the universe interact. But the standard model is unable to explain certain real-world observations, like dark matter or the absence of antimatter, so researchers are seeking discrepancies between predicted and measured properties of fundamental particles to look for new physics. 


So far, measurements of the electron’s magnetic moment have agreed with the standard model, but only to a certain level of precision. Now, Gerald Gabrielse at Northwestern University in Illinois and his colleagues have measured the property 2.2 times more precisely than ever before, finding it in agreement with the previous best measurement, in 2008. 


To do this, Gabrielse and his team trapped a single electron in a chamber with an ultra-stable magnetic and electric field, isolated from any external forces and cooled to just above absolute zero, and then measured the electron’s response as they changed the magnetic field. 


“This new measurement boasts the most precise measurement of a physical property of a fundamental particle ever, and therefore stands as the gold standard for precision measurements testing physicists’ current best theory of all the universe’s known particles and forces,” says Alex Keshavarzi at the University of Manchester, UK, who wasn’t involved in the research. 


While this new measurement agrees with the standard model, as the old one did, it can’t be used to fully test the theory because its predictions are actually less precise than the measurement. This is because the standard model relies on a number called the fine structure constant, a measure of the strength of electromagnetism between particles. Physicists can’t quite agree on the size of this constant, with two groups finding significantly different values for it. 


With a more precise and accurate fine structure constant, it should be possible to properly compare the new electron magnetic moment value with that predicted by the standard model. If at that point there is a discrepancy between the two, then new physics will be needed to explain it, such as a new structure for the electron, which is currently thought to be point-like and structureless. 

Post a Comment