One of nature's simplest elements is giving scientists a big headache after new research shows that protons and neutrons in helium atoms are not behaving as theory suggests they should. The mismatch between theoretical predictions of how these particles behave and what they're actually doing could point to new physics beyond the Standard Model, the reigning model that describes the zoo of subatomic particles.
In research published in April in the journal Physical Review Letters, physicists zapped a container of helium atoms with electrons to knock the helium nuclei into an excited state, causing the nucleus to temporarily swell up and deflate, like a chest breathing. The team found that the response of the protons and neutrons in the nucleus to the electron beam diverged significantly from what theory predicts — confirming conclusions drawn from experiments done decades ago. The new research proves that this mismatch is real, not an artifact of experimental uncertainty. Instead, it seems scientists simply do not have a firm enough grasp of the low-energy physics that govern interactions between the particles in the nucleus.
