Click here to download our latest paper as a .pdf file.

Phase 1 Results

This the first power spectrum taken with the phase 1 configuration of ADMX when cold. It shows the power in the cavity over a small frequency range. Most of the shape is due to the bandpass filter. The peak in the center is a test signal injected into the cavity.

Other Results

These recent results indicate where we've looked for Axions and not found them. Since they're plots of Dark Matter Density versus Axion mass, the way to interpret the this plot is:

"We are 90% confident that the density of KSVZ Axions with masses between 1.9 and 2.5 GeV must be less than 0.5 GeV/cm^3. Since the expected density of Dark Matter near the solar system is around 0.5 GeV/cm^3, we are 90% confident that dark matter is not made of Axions with masses between 1.9 and 2.5 GeV. Other Axion masses are still possible."

L.D. Duffy, P. Sikivie, D.B. Tanner,
S.J. Asztalos, C. Hagmann, D. Kinion,
L.J. Rosenberg, K. van Bibber, D.B. Yu, R.F. Bradley
Phys. Rev. D 74, 012006 (2006).

You can download this article here.

However, this statement comes with a few caveats. That is, we're 90% confident of this, with the assumptions that:

• all Dark Matter is made of Axions
• the density of Dark Matter at earth actually is the same as the expected density near the solar system
• There aren't two different populations of Axions with very different velocities, meaning that we should look for two separated bumps at half height instead of one bump at full height

If some of these assumptions are wrong, it may change parts of our claim. For example, if the earth is in a particularly low density patch of dark matter, or if only half of dark matter is axions, we can still claim: "We are 90% confident that the density of KSVZ Axions with masses between 1.9 and 2.5 GeV must be less than 0.5 GeV/cm^3.", but we can no longer claim "we are 90% confident that dark matter is not made of Axions with masses between 1.9 and 2.5 GeV."

The high resolution plot has a similar interpretation, except the numbers are a little different, and there is an extra assumption that the axions are quite cold.

Phys. Rev. D 69, 011101(R) (01 Jan 2004)

In the end, we'd like to be able to claim either:

"We are 90% confident that the density of axions with mass X micro-eV is Y GeV/cm^3, and therefore it seems that Z% of dark matter is made out of Axions"

-OR-

"We are 90% confident that the density of KSVZ or DFSZ axions of nearly any thermal distribution is below 0.045 GeV/cm^3 for all theoretically allowed axions masses (from about 1 micro-eV to 1 milli-eV). Because the expected dark matter density near earth is around 0.5 GeV/cm^3, we are confident that even if Axions exist, they do make up a significant amount of dark matter (less than 1%), and another explanation for Dark Matter must be sought"

At this point, we can stop doing our experiment and move on to either learning more properties of the axion, or looking for some other explanation of dark matter.