Any Light Particle Searches (ALPS)

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, large-scale detector commissioning and operation, dark-matter physics and cosmology. The required technologies are spin-offs of technologies which were developed for ground and space-based gravitational-wave detectors. The work supported by this award would build on these investments and would allow continued development of high performance optical techniques and devices which have commercial applications in the laser and optics industries.

The ALPS experiment under development at DESY in Germany is a 'light-shining-through-walls' search, where photons are projected to be converted into weakly interacting light particles which pass unimpeded through an opaque wall and convert (in part) back to photons behind the wall. The most famous of these particles are axions which require a strong magnetic field to convert to photons. Other particles which fall within the ALPS portfolio include hidden-sector photons which couple linearly to the electromagnetic field and do not require a static magnetic field. The planned ALPS@DESY experiments are the leading background-independent searches for axions and hidden sector photons. The improved sensitivity of ALPS would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar searches. The experiment only depends on the fundamental photon-axion interaction and not on solar models nor on assumptions about dark matter.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.