Physics researchers in Switzerland say they may have glimpsed the elusive sub-atomic Higgs boson particle, which many scientists believe is one of the fundamental building blocks of the universe. But they stopped short of claiming a discovery, saying experiments at the Large Hadron Collider near Geneva have yielded “exciting,” but inconclusive, evidence the particle exists.

The Higgs boson was first theorized by British physicist Peter Higgs and others more than 40 years ago. Sometimes known as the “God particle,” it could help explain why everything in the universe has mass and weight. It is a significant missing piece of the so-called “Standard Model” of modern physics, a “rule book” for the interaction of particles and forces throughout the cosmos.

Finding the Higgs boson is one of the primary missions of the Large Hadron Collider, a $10-billion particle accelerator operated by the Switzerland-based European Organization for Nuclear Research. Scientists there have been smashing protons together at near-light speeds, hoping to produce clear signs of the mysterious boson.

Scientists say further research might eventually prove the Higgs boson is real. Or it could disprove its existance, challenging some of the basic tenets of modern physics.