ApplicationTitle:Search for dark-matter axions with the Axion Dark Matter eXperiment

David B. Tanner (Principal Investigator) Neil S. Sullivan(Co-Investigator) University of Florida, Gainesville, FL

Abstract:

Most of the matter in the Universe is composed of some unknown substance, called “dark matter,” that interacts with ordinary matter via the gravitational force, but in no other way observed so far. One candidate dark-matter particle is the axion, a particle originally postulated to explain why the strong force is symmetric under the combination of charge conjugation (C) and parity (P). If the axion mass is of order 2–40 µeV, it could form the dark-matter halo of our galaxy. Halo axions may be detected by their conversion into photons in a tunable high-quality-factor microwave cavity permeated by a strong external magnetic ?eld. The corresponding resonant frequencies are in the microwave part of the electromagnetic spectrum: 0.5–10 GHz. The Axion Dark Matter eXperiment, ADMX, uses near quantum-limited superconductivity-based amplifiers, with both cavity and amplifier operated at ultralow temperatures (around 0.1 degree above absolute zero) to reduce background and technical noise. The Generation-2 ADMX detector is the first experiment fully sensitive to high-priority models of axions as dark matter. The Florida ADMX group will participate in supporting operations of the dilution refrigerator used to cool the experiment, in operations of the detector, and in analysis of ADMX data. The group also will operate a pilot experiment that uses an LC resonant circuit to search for very light axions, with masses around 0.08–0.2 µeV (corresponding to photon frequencies of 20–50 MHz. A final task is to carry out research aimed at reduction of risks associated with the deployment of a four-cavity array that is tunable over 1.4–2.1 GHz for use by ADMX to search the 5–9 µeV mass range, as well as the development of cavities for still higher frequencies.