Senin, 29 Juli 2013

Still No Sign Of Violation Of Lorentz Symmetry

The more they test it, the more precise they measure the validity of the foundations of Relativity. This time, the measurement comes from a new technique of measuring the the transition energy between two electron energy states of dysprosium.

The team chose dysprosium because it has a pair of closely-spaced energy states that involve orbitals where electrons travel at very different speeds. Because of this speed difference, a change in the electron’s kinetic energy due to a change in the atom’s orientation would affect the two states very differently. The researchers illuminated a beam of dysprosium atoms with two laser beams to excite them to state B (via another state) and then drove the transition to A with a precisely calibrated microwave beam. To measure the transition energy, they found the microwave frequency most effective at driving the transition. The team repeated the experiment many times over a period from 2010 to 2012.

The orbitals of the atoms were oriented to some extent by the polarization of the exciting laser beams. So if the electrons’ kinetic energy depended on their direction of motion, the team would have seen a daily oscillation in the transition energy from the earth’s rotation. Similarly, if there were any effect from the earth’s position in the sun’s gravitational field (violating local position invariance), there would have been an annual oscillation.

There are many different ways to violate Lorentz invariance, so researchers in the field have developed a standard set of parameters to characterize different types of violations. Hohensee and his colleagues measured eight of the nine parameters that describe any dependence of the electron’s maximum attainable speed on the speed and direction of the lab’s reference frame. They significantly improved limits from previous experiments for four of them, one by a factor of 10. Their new limits on local position invariance for electrons are 160 times more precise than previous ones.

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