Laying the groundwork for what they said would be a new era of scientific cooperation, leaders of European and American particle physics initiatives signed an agreement at a White House ceremony on Thursday to share the spoils of their research in the coming decades.

Scientists and diplomats said the deal — signed by the Department of Energy, the National Science Foundation and CERN, the European Organization for Nuclear Research — allows the United States to continue to collaborate on the world’s flagship experiment, CERN’s Large Hadron Collider, where the long-sought Higgs boson was discovered three years ago. For the first time, CERN will now be able to collaborate on projects in the United States, a necessity in an age when big scientific experiments are too expensive for any one country or even one continent to foot on its own.

“That’s a big deal, a big change,” James Siegrist, associate director of the Office of Science in the Department of Energy, said in an interview. “Our research programs in the U.S. and Europe are now deeply intertwined by the signing of this agreement.”

John P. Holdren, President Obama’s chief science adviser, called the pact “a model for the kinds of international scientific collaboration that can enable breakthrough insights and innovations.”