An Experiment to Search for Axions

C. Hagmann, W. Stoeffl, K. van Bibber
Lawrence Livermore National Laboratory
7000 East Ave, Livermore, CA 94550

E. Daw, D. Kinion, L. Rosenberg

Dept of Physics, Massachusetts Institute of Technology
77 Massachusetts Ave, Cambridge, MA 02139

P. Sikivie, N. Sullivan, D. Tanner

Dept of Physics, University of Florida
Gainesville, FL 94720

D. Moltz

Nuclear Science Division, Lawrence Berkeley Laboratory
1 Cyclotron Rd, Berkeley, CA 94720

F. Nezrick, M. Turner

Fermi National Accelerator Laboratory
Batavia, IL 60510

N. Golubev, L. Kravchuk

Institute for Nuclear Research of the Russian Academy of Sciences
60th October Anniversary Prospekt 7a, Moscow 117312, Russia

What is an axion?

The axion   is a hypothetical elementary particle proposed to explain the absence of an electrical dipole moment for the neutron1, 2. The axion has no electric charge, no spin, and interacts with ordinary matter (electrons, photons, quarks, etc.) only very weakly. Even though the axion -- if it exists -- should have only a tiny mass, axions would have been produced abundantly in the Big Bang, and relic axions are an excellent candidate for the dark matter in the universe.

How do we detect axions?

Our experiment attempts to detect axions trapped in the dark halo of our galaxy. The halo density at our location in the galaxy is about 5*10-25 g/cm3. Models predict that axions may have a mass of about 2*10-38 g, so we expect about 1013 axions per cubic centimeter locally.3, 4

In the presence of a static magnetic field, there is a small probability for axions to decay into microwave photons via the "Primakoff effect."4 Our detector consists of a high-Q tunable microwave cavity inside a large superconducting magnet about 1 meter long with a bore diameter of 60 cm. Any microwave signal from the cavity is amplified by a very low-noise GaAs amplifier. The expected signal is very faint; it corresponds to only a few hundred axion decays per second.

To reduce the noise to the required acceptable level, we cool the cavity to a temperature of 1.5 Kelvin (1.5 degrees Celsius above absolute zero). Unfortunately, the frequency of the axion decay is not known, so we slowly sweep the cavity resonance over the range of possible frequencies.

We plan to run our detector for 3 years starting in mid 1995 to cover the frequency range from 300 MHz to 3 GHz. The "exclusion plot" of masses and coupling strengths that we will be able to detect is shown below.


References:

  1. R. Peccei and H. Quinn, Phys. Rev. Lett. 38 (1977) 1440.
  2. S. Weinberg, Phys. Rev. Lett. 40 (1978) 223; F. Wilczek, Phys. Rev. Lett. 40 (1978) 279.
  3. M. Dine et al., Phys. Lett. 104B (1981) 199; A. Zhitnitskii, Sov. J. Nucl. Phys. 31 (1980) 260.
  4. J. Kim, Phys. Rev. Lett. 43 (1979) 103; M. Shifman et al., Nucl. Phys. B166 (1980) 493.
  5. P. Sikivie, Phys. Rev. Lett. 51 (1983) 1415.
For more information on the axion experiment, contact:
Christian.Hagmann@quickmail.llnl.gov -- Christian Hagmann

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