Decades-Long Quest Reveals Details of the Proton’s Inner Antimatter

Physicists have glimpsed an imbalance in the types of antimatter that swim in the sea of quarks and gluons that make up the proton. A shoestring experiment 20 years in the making, called SeaQuest, has found that there are more down antiquarks than up antiquarks in the proton sea: on average, 1.4 down antiquarks for every up antiquark. The asymmetry could help to decide which of the competing theoretical models of the proton will come out on top.