In a vast, dark hall, they're searching for a single person who makes almost no sound. That's how physicists hunt for sterile neutrinos — ghostly particles that pass through matter, leaving barely a trace.
Inside the accelerator, particles collide, and for a fleeting moment a B meson is born — a heavy particle that lives for less than a billionth of a second. Usually, it decays into a shower of debris, but sometimes it transforms into just two particles: a muon and a neutrino. This rare path is like a lottery where the winning ticket appears once in every two million draws.
A proton can't be seen as a simple ball. If you hit it with a photon, it can absorb energy and jump into an excited state, like a bell that starts ringing at a certain frequency after being struck. These states are called nucleon resonances, and they live very briefly before decaying into other particles.
A strange visitor came to light in a fleeting flash. A beam of photons struck a deuterium nucleus (heavy hydrogen), and in the cascade of produced particles, detectors noticed something unusual. At a certain combination of masses and momenta, the signal sharply intensified, as if a new particle had appeared for a brief moment.