Development and characterization of superconducting microwave cavities for dark matter search

This project's goal is to analyze the latest improvements in the development of haloscopes. Haloscopes are microwave resonant cavities, whose function is to detect axions, DM candidates that could also solve the strong CP problem of the standard model of particle physics. These instruments were first proposed in 1985 by P. Sikivie, who made evident that such devices need to be immersed in high B field and to exhibit high Q factors. With copper cavities, quality factors exceeding 1E5 cannot be obtained due to the anomalous skin effect; therefore researchers have turned to superconducting cavities, both coated and bulk. The required sensitivity to probe the most plausible parameter space is reached with microwave cavities whose quality factor is comparable with or exceeding 1E6. Within the QUAX collaboration, experimental efforts are focused on NbTi coated microwave cavities in high B field. Optimization of the cavity design and characterization methods employed will be described. Experimental results obtained with a copper cavity sputtered with NbTi will also be reported.