High resolution search for dark-matter axions

We have performed a high resolution search for galactic halo axions in cold flows using a microwave cavity detector. The analysis procedure and other details of this search are described. No axion signal was found in the mass range $1.98–2.17\mu \mathrm{eV}$. We place upper limits on the density of axions in local discrete flows based on this result.

Figure 1

Schematic diagram of the receiver chain.

Figure 2

Sketch of the ADMX detector.

Figure 3

Power distribution for a large sample of 1-bin data.

Figure 4

Power distribution for a large sample of 8-bin data.

Figure 5

Power distribution for a large sample of 4096-bin data.

Figure 6

An environmental peak as it appears in the MR search (top) and the 64-bin HR search. The unit for the vertical axis is the rms power fluctuation in each case.

Figure 7

HR filter response calibration data (512 bin average). The power has been normalized to the maximum power output.

Figure 8

Sample 4096-bin spectrum before correction for the cavity-amplifier coupling. The line is the fit obtained using the equivalent circuit model.

Figure 9

Illustration of the addition scheme for the 2, 4 and 8-bin searches. The numbers correspond to the data points of the 1-bin search. Numbers within the same box are bins added together to form a single datum in the $n$-bin searches with $n>1$.

Figure 10

97.7% confidence level limits for the HR 2-bin search on the density of any local axion dark matter flow as a function of axion mass, for the DFSZ and KSVZ $a\gamma \gamma$ coupling strengths. Also shown is the previous ADMX limit using the MR channel. The HR limits assume that the flow velocity dispersion is less than $\delta v_2$ given by Eq. (8).