[davrosthedalek]

The US is not even a member of CERN.

[rmcpherson]

True but the U.S. has contributed hundreds of millions to the LHC and still does. https://www.aip.org/fyi/2008/us-contribution-lhc-budget-and-...

[Iwan-Zotow]

Accelerator itself is mostly CERN responsibility, but detectors are usually international collaborations. US contributed a lot to the CMS detector at LHC (as well as Russia, another non-member state).

https://science.energy.gov/~/media/hep/pdf/files/pdfs/uslhcc...

http://cms.web.cern.ch/news/using-russian-navy-shells