Dr Shriram Jois (RHUL)

The axion was hypothesized to explain the invariance of strong interactions under the transformations P and CP. The theory predicts that a large number of relic axions could have been produced in the big bang. If discovered, it could account for the majority of the dark matter in the Milky Way galaxy. This hypothetical particle is being searched in a microwave cavity in the ADMX collaboration. The experiment includes a high Q microwave cavity inside the bore of an 8-T solenoid magnet. The whole setup is cooled down to cryogenic temperatures. The application of a strong magnetic field provides an alternate path for axions to decay into photons in a process called Sikivie conversion. Because the mass of the axion is unknown, the cavity is slowly tuned. The Run 1B of the ADMX run covered a frequency range of 680 – 800 MHz.

The data from the experiment are recorded in two channels: a medium resolution and a high-resolution channel. While the medium resolution channel searches for virialized axion flow, the high-resolution channel searches for unvirialized axion flow. Due to motions of the Earth in the Milky Way galaxy relative to the axion flow, the signal is expected to undergo a diurnal and annual frequency modulation. This frequency modulation is expected to be around 10 mHz per 100 sec scan at a cavity frequency of 1 GHz. The high-resolution data are sensitive to such modulations and therefore must be considered in the analysis. The analysis includes various cuts to identify and remove the synthetic axion injections, identify and remove the non-persistent triggers and investigate the frequency modulation of the axion signal. In this talk, I present the results of the high-resolution data analysis of Run 1B of the ADMX run.

A microwave cavity on a test bench