“There is enormous angst in the field,” said Michael S. Turner, a physicist and cosmologist at the University of Chicago, who attended the Caltech meeting.

After canceling the Superconducting Super Collider, which would have been the world’s most powerful physics machine, in 1993, and shutting down Fermilab’s Tevatron in 2011, the United States no longer has a machine of its own to explore the frontier where new particles and forces in the universe might be discovered. The only collider now operating in the United States is the Relativistic Heavy Ion Collider on Long Island, which shoots gold ions at each other to study the interactions of quarks. It, too, is threatened to be shut down.

Fermilab’s biggest project going forward is a plan to shoot a beam of neutrinos, ghostlike particles, 800 miles through the earth to a detector at the old Homestake gold mine in Lead, S.D., to investigate their shape-shifting properties.

The results could bear on one of the deep-seated and intractable problems in cosmology, namely why the universe is made of matter and not antimatter, but there is not enough money in the project’s budget to put the detector below ground, at the bottom of the mine, where it would be sheltered from cosmic rays and able to observe neutrinos from distant supernova explosions, instead of on the surface.

Americans who want to taste the thrills of the frontiers of high-energy physics have to cast their eyes east to CERN’s collider, which is set to dominate the field for the next 20 years. Or they might look west, to Japan, which is budgeting about $120 billion in stimulus money to help recover from the disaster at the Fukushima nuclear power plant after the earthquake and tsunami in 2011 and wants to use some of it to host the next big machine, the International Linear Collider, which would be 20 miles long and could manufacture Higgs bosons for precision study.