Axion

In physics Axion refers to a hypothetical elementary that it can be postulated in quantum chromodynamics to resolve the problem of the electrical neutrality of the neutron. This strong CP problem arises from the fact that it may lead to quantum fluctuations of the electric fields of the neutron according to a special vacuum term. This would have ≈ 10-16 e · cm exist an electric dipole moment dn, was instead even with dn ≤ 10-25 e · cm yet none measured.

• 3.3.1 ADMX

Theoretical background

In contrast to the weak interaction are in the strong interaction, the discrete symmetries C ( charge reversal, the replacement of all particles by their antiparticles ), P (parity, space reflection ) and T ( time reversal ) unbroken. One consequence is the vanishing electric dipole moment of the neutron.

In particular, it is the combination CP an unbroken symmetry, although the quantum contains a CP violating component in the effect. This is as strong CP problem (strong CP problem) known. One solution is the Peccei -Quinn -Weinberg - Wilczek theory at the price of a new, light, weakly interacting particle which Frank Wilczek, named after the American detergent Axion.

There is, for a model of strongly interacting KSVZ - axions and on the other, the less strongly interacting DFSZ - axions.

Candidate for dark matter

Are axions, in addition to the neutrinos and the equally postulated WIMPs and MACHOs, considered a potential candidate for solving the problem of dark matter.

Detection experiments

Laboratory experiments

In the laboratory experiments, it is " light through the wall " experiments, in which a laser beam passes through a magnetic field and is subsequently blocked by a wall. On the other side of the wall is a stationary magnetic field perpendicular to the beam of the same strength and at the end of this field to the laser a quantum (photons) of calibrated detector.

The trick is, that is caused by the Axion Primakoff effect with the help of a virtual photon by the magnet in front of the wall formed by the reverse effect is transferred to the other side of the wall back to a quantum of light. The incoming light interacts with the magnetic field fluctuates in a different form, which may spread beyond the wall. Behind the wall again occur fluctuations of the new state back to the original character. Parts of the photons could thus circumvent the wall so that they would be detectable. Proof of photons behind the wall would demonstrate the short-term presence of light in the form of axions. Changes in the fields automatically affect the detected amount of light. This would allow conclusions on the used Axion amount.

Helioskope

Crystalline detectors

Within an electric field, the photon coupling Axion is coherent if the Bragg equation is satisfied. Known experiments are Solax, COSME and DAMA.

Primakoff telescopes

In the Primakoff telescopes is searched by using the Primakoff effect for axions (see CAST experiment at the CERN research center ). Through the Primakoff effect is an Axion in an external magnetic field, eg converted at CAST in the field of an LHC prototype magnet with 9 Tesla strength, into a photon with energies in the keV range. This can then be detected in particle detectors such as a CCD.

Mössbauer telescopes

Here, the Axion is detected by resonant excitation of an atomic nucleus, similar to the excitation by photons in the Mossbauer effect. A first generation of the experiment is under construction.

Haloskope

ADMX

In the U.S. Large - Scale Axion Search ( ADMX ) is a collaboration. Participating institutions are:

• The Lawrence Livermore National Laboratory ( LLNL ),
• The Massachusetts Institute of Technology (MIT),
• The University of Florida ( UF),
• The Lawrence Berkeley National Laboratory ( LBNL ),
• The Fermi National Accelerator Laboratory ( FNAL )
• The University of Chicago and
• The United Institute of Nuclear Research ( Institute for Nuclear Research), Moscow.

The experiment is built at the Lawrence Livermore National Laboratory. For its construction were experiences from the two previous experiments, the University of Florida experiment and the Rochester Fermilab Brookhaven experiment ( RBF) are considered.

The objectives of the experiment are

• To increase the quality of the experiment so far that can be KSVZ - axions evidence from our halo and
• The mass range of 1.3 μeV / c ² < ma < 13 μeV / c ² fully to detect.

The ADMX experiment used a so-called Sikivie detector. Here, an Axion is generated within a static magnetic field via the Primakoff effect. The obtainable wavelength of the photon is determined by the resonance frequency, ie the size of the container limits: the cylinder used is 1 m long and has a diameter of 0.5 m. The by a superconducting solenoid ( electromagnet) provided magnet volume is B02 * V <11 T2m3.