Researchers at the European Organization for Nuclear Research (CERN) in Switzerland have demonstrated that the proton and its antimatter doppelganger, the antiproton, are identical to a new high degree of precision. The motivation behind the research is to solve one of physics’ biggest mysteries: why the matter in our universe can exist. According to theory, the big bang that birthed the cosmos 13.8 billion years ago should have generated equal amounts of matter and antimatter—substances that mutually annihilate upon contact. Yet antimatter only exists in short-lived quantities in the universe today, forged through astrophysical processes and in particle colliders like those at CERN. For some as-yet-unknown reason, matter predominated over antimatter as the big bang unfolded. See also: Antimatter; Big bang theory; Matter (physics); Physics; Universe
Presumed to be at the root of this matter-antimatter asymmetry are minute differences in the particles’ characteristics that go beyond their manifestly opposite charges and other contrasting properties. (For example, the electron is negatively charged, and its antimatter counterpart, the positron, bears a positive charge.) These differences are referred to as CP (charge-parity) violations. Although instances of CP violation have emerged for various sorts of particles, these deviations do not come anywhere close to accounting for matter’s abundance over antimatter in the universe. See also: CP symmetry and its violation
The new results add to this enigma by finding that, at a level of precision 350 times greater than the previous record, antiprotons possess the same value as protons for a property known as the magnetic moment. This fundamental property describes how particles orient themselves when exposed to a magnetic field. To achieve this measurement, an experiment called BASE (Baryon Antibaryon Symmetry Experiment) had to electromagnetically trap antiprotons in airless, nearly pure vacuum chambers to avoid destructive encounters with matter. The experiment employed a novel approach of probing two antiprotons at the same time, integrating separately measurable properties to arrive at an extremely precise reading of their magnetic moment. See also: Electron; Elementary particle; Magnetism; Magneton; Particle trap
In accordance with the laws of physics, protons and antiprotons remain indistinguishable in this regard. But the BASE scientists believe that by making further enhancements to their experiment, they can obtain a two-fold better gauging of the magnetic moment over the next decade, perhaps revealing at last a critical way that protons and antiprotons do, in fact, diverge. Along with continuing efforts to tease out CP violations across the host of particles discovered over the past half-century, and which today comprise the robust Standard Model, researchers hold out hope that we will soon learn the reason for matter’s survival. See also: Standard model