In search of the axion particle with RF cavities in cast experiment at CERN

Abstract

Axion is a pseudo scalar boson that is predicted to solve the strong CP problem and therefore cast light upon curious CP invariance of the strong nuclear interactions. It is also a promising candidate to be the building block of the dark matter. CAST was invented more than 20 years ago as an axion helioscope, searching for high energy solar axions and it has exceeded the expectations throughout its operation. In a published article in 2017, CAST has declared a new research program to explore galactic halo (dark matter) axions. CAST-CAPP detector searches for dark matter axions using four microwave cav ities that operate in 4.7-5.4 GHz band corresponding to ∼19-22 µeV axion mass. It has started operation in 2019, after several years of design, installations and tests. CAST-CAPP is unique in a sense that it utilizes multiple portable rectangular cavities that can be phase-matched in order to amplify the axion signal. In 2 data taking runs, preliminary results indicate that CAST-CAPP has pushed the limits of axion search by exploring new regions in the parameter space.