Joe Incandela, leader of one of the two independent teams at the world's biggest atom smasher, told a packed audience of scientists at the European Center for Nuclear Research (CERN) that the data has reached the level of certainty needed for a discovery.
But he has not yet confirmed that the new particle is indeed the tiny and elusive Higgs boson, which is believed to give all matter in the universe size and shape.
Meanwhile, the second team of physicists also claimed they have observed a new particle, probably the elusive Higgs boson.
The announcements were made to huge applause by scientists including Peter Higgs who first suggested the existence of the particle in 1964.
In a statement, CERN said the particle they found at LHC is "consistent with (the) long-sought Higgs boson," but more data was needed to identify the find.
"We have reached a milestone in our understanding of nature," said CERN Director General Rolf Heuer.
"The discovery of a particle consistent with the Higgs boson opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle's properties, and is likely to shed light on other mysteries of our Universe," Heuer said.
Finding the Higgs would validate the Standard Model, a theory which identifies the building blocks for matter and the particles that convey fundamental forces.
Higgs boson is believed to exist in an invisible field created by the Big Bang some 13.7 billion years ago. When some particles encounter the Higgs, they slow down and acquire mass, according to the theory. Others, such as particles of light, encounter no obstacle.