The electron has been weighed with unprecedented precision, researchers report February 19 in Nature. Its new and improved mass, 17 times as precise as the previous best estimate, is 0.000548579909067 atomic mass units. (An atomic mass unit is one-twelfth the mass of a carbon-12 atom, or 1.66 trillionths of a trillionth of a gram.) German researchers calculated the mass by analyzing a lone electron bound to a bare carbon nucleus.
Adding a few decimal places of confidence may seem trivial, but physicists need precise measurements of known particles to have a chance of discovering a new particle or force that interacts with them.
