Physics of Fundamental Symmetries and Interactions {PSI2010 A torsion pendulum based axion search

Despite two decades of experimental e_ort, the elusive axion has yet to be discovered. Nevertheless, it remains a well-motivated solution to the strong CP problem and a promising dark matter candidate. Most searches use the axion-two-photon coupling to probe for axions that are generated in the sun, remnants from the big-bang or created in the laboratory. Using techniques inspired by torsion pendulum based tests of gravity, we have constructed a new torsion pendulum experiment that looks for a macroscopic parity and time-violating force mediated by virtual axions. For an axion mass of 1 meV, we have improved the limit on this force by ten orders of magnitude, and thus, have opened another path to look for very heavy axions.