Inside the Hunt for a Ghost Particle

Even for a particle physicist, Janet Conrad thinks small. Early in her career, when her peers were fanning out in search of the top quark, now known to be the heaviest elementary particle, she broke ranks to seek out the neutrino, the lightest.

In part, she did this to avoid working as part of a large collaboration, demonstrating an independent streak shared by the particles she studies. Neutrinos eschew the strong and electromagnetic forces, maintaining only the most tenuous of ties to the rest of the universe through the weak force and gravity. This aloofness makes neutrinos hard to study, but it also allows them to serve as potential indicators of forces or particles entirely new to physics, according to Conrad, a professor at the Massachusetts Institute of Technology. “If there’s a force out there we haven’t seen, it must be because it is very, very weak—very quiet. So looking at a place where things are only whispering is a good idea.”