CMS EXO Workshop 2025 at CERN

The CMS EXO working group gathered at CERN from January 26 to 28 to discuss recent developments in the landscape of searches looking for exotic signatures beyond the Standard Model of Particle Physics (BSM). During this workshop, many promising searches were presented in the dedicated sessions of the three different subgroups looking for non-hadronic signatures, signatures of long-lived particles as well as signatures including jets and missing energy. In these sessions, there were even some excesses to be reported that warrant further investigation. 

The ETP BSM searches group was represented with two lightning talks by PhD candidates. Marcel Gaisdörfer reported progress on the search for semivisible jets using scouting data, a specialized data stream to get around storage limitations while also lowering trigger thresholds. Semivisible jets originate from so-called “dark hadrons” that don’t interact electromagnetically or strongly with but partially decay into Standard Model particles. The remaining stable invisible “dark hadrons” are a prime candidate for dark matter. Johannes Hornung presented an update on the first search for pseudoscalar bosons from Higgs boson decays in the four-kaon final state. Pseudoscalar bosons are introduced by many BSM theories in the form of so-called “Axion-Like Particles” or additional Higgs bosons. While not being dark matter candidates themselves most of the time, a discovery of these particles would tighten the current broad landscape of BSM theories.

With the data-taking of the current LHC Run finishing in mid 2026, the future task was clearly set for the collaborators: Analyze the new data! With all of this new data and innovative new techniques, ETP researchers will be busy for years to come to search for possible hints of new physics in this large dataset delivered by the LHC.