Multiple astronomical observations have established that about 85% of the matter in the universe is not made of known particles. Deciphering the nature of this so-called Dark Matter is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. One of the most exciting quests in particle physics is the search for new particles beyond the Standard Model of particle physics. Extensions of the standard model predict not only new particles with masses above the electroweak scale (about 100 billion electron-volts, eV), but also so-called WISPs (Weakly Interacting Sub-eV Particles). The most famous WISP candidate is the axion, which has been introduced to explain the smallness of Charge-Parity (CP) violation in Quantum ChromoDynamics and which turns out to also be a prime candidate for a constituent of the dark matter in the universe. Similarly, axion-like particles, light spin 1 particles called "hidden sector photons," seem to occur naturally in realistic embeddings of the standard model into string theory. It is therefore an important and fundamental question whether any of these weakly-interacting light particles exists.
The Any Light Particle Search (ALPS) experiment will give students and postdoctoral scientists the opportunity to develop scientific skills from a diverse set of disciplines spanning lasers and optics, electronics and feedback control systems, vacuum and cryogenics, computational methods and data analysis algorithm development. The required technologies are spin-offs of technologies that were developed for ground- and space-based gravitational-wave detectors. The work supported by this award will build on these investments and continue the development of techniques and devices which have commercial applications in the laser and optics industries.
The ALPS experiment is a "shining light through a wall" study. In such an experiment, laser light traveling through a strong magnetic field may (in part) be converted to axions or axion-like particles. These particles are so weakly interacting that they can pass unimpeded through an opaque wall and then convert (in part) back to photons in a second "regeneration" region of a strong magnetic field where they are detected. The most sensitive laboratory setup thus far is the first stage of ALPS I concluded in 2010. With major upgrades in magnetic length, laser power and the detection system, the proposed ALPS II experiment aims at improving the sensitivity by a few orders of magnitude for the different WISPs. This award will enable US participation in the ALPS experiment by bringing the group's expertise in seismic isolation and suspension systems.