Testing the Neutrality of Neutrons

The Standard Model describes most of the properties of fundamental particles, however it is far from being perfect. The Standard Model cannot explain why charge is experienced in electron units, nor how certain particles acquire neutral charge and if whether the charge of an atom with equal numbers of protons and electrons is really null. Stanford University researchers believe that they can test and answer to a part of these questions by developing the ultimate neutrality experiment.


If in fact, the electron charge is not the basic charge quanta, the experiment would be able to reveal it. They believe that an alternative "Grand Unified" theory could explain much of how charge is quantized and how the atom actually experiences null charge. "Grand Unified" theory would provide with the basis to link three of the basic forces in the universe, electromagnetism, the strong nuclear force and the weak nuclear force, opposed to the "Theory of Everything" which would include gravity as well.

Stanford University researchers already showed that a magnetic monopole carrying a non-quantized electric charge could exist under time reversal symmetry violation.

"This suggests that we have to rethink our notion of charge quantization and the conditions under which it holds," sayd Asimina Arvanitaki, Stanford University physicist. Electric charge could be measured with an accuracy of 10^-20 to 10^-28e, a hundred million times better that previously thought possible. "This is similar to measuring the distance between the earth and the sun to an accuracy better than the size of a nucleus," said Arvanitaki.

The experimental device is an atom interferometer, able to detect differences between atoms by measuring atom wavelengths. The setup consists of a primary 10 meter cylinder positioned vertically, inside which two other cylinders spaced at a certain distance are placed. Rubidium atoms are being fed into the cylinder through the bottom of the device, and accelerated at a speed of 10 meters per second.

A pulsed laser beam in reflected of the atoms in order to decompose the atom's wavefunctions into two space-time trajectories, which are latter recombined and interfered. Once the beam splitter achieves "large momentum transfer", the difference in momentum can reach differences of 1 meter per second, thus this component will be much higher than the other, extending into the upper inner cylinder, while the other never leaves the lower cylinder.

By applying a positive electric potential on the upper cylinder and a negative electric potential on the lower one, researchers reckon they will be able to determine whether or not the atoms are indeed electrically neutral, as wavefunction components react in relation to the voltage applied to the respective cylinder. In case the atoms are not neutral, once a phase shift is introduced between the two wavefunctions, one should experience an oscillation frequency higher than the other.