Physicists set new limits on hypothetical new particles called the extra “Z-boson”

May 1st, 2009 - 3:20 pm ICT by ANI  

Large Hadron Collider Washington, May 1 (ANI): A group of physicists at the University of Nevada, Reno, US, are reporting a refined analysis of experiments on violation of mirror symmetry in atoms that sets new constraints on a hypothesized particle, the extra Z-boson.

“It is remarkable that the low-cost atomic precision experiments and theory are capable of constraining new physics at the level competitive to colliders,” said Andrei Derevianko, an associate professor in the College of Science’s Department of Physics.

Derevianko has been able to define new limits without needing something like a 6 billion dollars Large Hadron Collider (LHC), an enormous particle accelerator in Europe that is not yet fully operational.

“This is like David and Goliath, we are just a small group of people able to better interpret the data on violation of mirror symmetry in atoms. Our work indicates less of a possibility for extra Z-bosons, potential carriers of the fifth force of nature. It is possible the LHC will be able either to move the mass limit higher or discover these particles,” he said.

Derevianko and his colleagues have determined the coupling strength by combining previous measurements made by Dr. Carl Wieman, a Nobel laureate in physics, with high-precision calculations in a cesium atom.

The original work by Wieman on violation of mirror symmetry in atoms used a table-top apparatus at the University of Colorado in Boulder, Colorado.

The Boulder team monitored a “twinge” of weak force in atoms, which are otherwise governed by the electromagnetic force.

The Standard Model of elementary particles, developed in the early 1970s, holds that heavy particles, called Z-bosons, carry this weak force.

In contrast to the electromagnetic force, the weak force violates mirror symmetry: an atom and its mirror image behave differently.

This is known to physicists as “parity violation.”

The Boulder group’s experiment opened the door to new inquiry, according to Derevianko.

“It pointed out a discrepancy, and hinted at a possibility for new physics, in particular, extra Z-bosons,” he said.

In contrast to previous, less accurate interpretations of the Boulder experiment, Derevianko’s group has found a perfect agreement with the prediction of the Standard Model. This agreement holds important implications for particle physics.

“Atomic parity violation places powerful constraints on new physics beyond the Standard Model of elementary particles. With this new-found precision, we are doing a better job of ‘listening’ to the atoms,” Derevianko said.

By refining and improving the computations, Derevianko said there is potential for a better understanding of hypothetical particles (extra Z-bosons), which could be carriers of a so-far elusive fifth force of nature. (ANI)

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