Cosmic Axion Spin Precession Experiment (CASPEr)
a laboratory table-top search for dark matter
The nature of dark matter is one of the most important open problems in modern physics. While the Weakly Interacting Massive Particle (WIMP) is a well motivated candidate, it is heavily constrained by null results from a variety of experiments, and the Large Hadron Collider has placed stringent constraints on scenarios such as supersymmetry that have provided the theoretical basis for WIMP dark matter. Thus, it is essential to develop techniques to search for a wide class of dark matter candidates, and axion dark matter stands out as being firmly based on theoretical foundations. A discovery of the axion would not only be the discovery of dark matter and a possible resolution of the strong CP problem of the Standard Model, but would also provide insights into the high-energy scales from which the axion arises, near the fundamental scales of particle physics such as the scale of grand unification and the Planck scale.
Remarkably, axion dark matter can have experimental signatures detectable in laboratory-scale low-energy precision experiments. The search strategy that we are exploring is based on spin precession caused by the background axion field, is sensitive to a wide range of axion masses, and has the potential to detect axion-like dark matter with coupling strength many orders of magnitude beyond the current astrophysical and laboratory limits, and all the way down to the Quantum Chromodynamics (QCD) axion.
Some of the laboratory techniques and concepts we use are: cryogenics (temperature down to 4 K), magnetic resonance, radiofrequency circuits, precision magnetic field sensors (eg, SQUIDs), superconducting magnets and magnetic shielding, low-noise analog and digital electronics, and lasers for optical pumping.
Have a look at the video below for a summary of our approach. Also, thanks to BU Today for putting together this article about our experiment.