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RE: Parity Violation
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For One Tiny Instant, Physicists May Have Broken a Law of Nature

For a brief instant, it appears, scientists at Brook­haven National Laboratory on Long Island recently discovered a law of nature had been broken.
Action still resulted in an equal and opposite reaction, gravity kept the Earth circling the Sun, and conservation of energy remained intact. But for the tiniest fraction of a second at the Relativistic Heavy Ion Collider (RHIC), physicists created a symmetry-breaking bubble of space where parity no longer existed.
Parity was long thought to be a fundamental law of nature. It essentially states that the universe is neither right- nor left-handed - that the laws of physics remain unchanged when expressed in inverted coordinates. In the early 1950s it was found that the so-called weak force, which is responsible for nuclear radioactivity, breaks the parity law. However, the strong force, which holds together subatomic particles, was thought to adhere to the law of parity, at least under normal circumstances.
Now this law appears to have been broken by a team of about a dozen particle physicists, including Jack Sandweiss, Yale's Donner Professor of Physics. Since 2000, Sandweiss has been smashing the nuclei of gold atoms together as part of the STAR experiment at RHIC, a 2.4-mile-circumference particle accelerator, to study the law of parity under the resulting extreme conditions.
The team created something called a quark-gluon plasma - a kind of "soup" that results when energies reach high enough levels to break up protons and neutrons into their constituent quarks and gluons, the fundamental building blocks of matter.
Theorists believe this kind of quark-gluon plasma, which has a temperature of four trillion degrees Celsius, existed just after the Big Bang, when the universe was only a microsecond old. The plasma "bubble" created in the collisions at RHIC lasted for a mere millionth of a billionth of a billionth of a second, yet the team hopes to use it to learn more about how structure in the universe - from black holes to galaxies - may have formed out of the soup.
When the gold nuclei, travelling at 99.999% of the speed of light, smashed together, the plasma that resulted was so energetic that a tiny cube of it with sides measuring about a quarter of the width of a human hair would contain enough energy to power the entire United States for a year.
It was the equally gargantuan magnetic field produced by the plasma - the strongest ever created - that alerted the physicists that one of nature's laws might have been broken.
Sandweiss and the team - which includes Yale physics research scientists Evan Finch, Alexei Chikanian and Richard Majka - found that quarks of a like sign moved together: Up quarks moved along the magnetic field lines, while down quarks travelled against them. That the quarks could tell the difference in directions suggested to the researchers that symmetry had been broken.

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Parity–time symmetry
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Title: Observation of paritytime symmetry in optics
Authors: Christian E. Rüter1, Konstantinos G. Makris2, Ramy El-Ganainy2, Demetrios N. Christodoulides2, Mordechai Segev3 & Detlef Kip1

One of the fundamental axioms of quantum mechanics is associated with the Hermiticity of physical observables. In the case of the Hamiltonian operator, this requirement not only implies real eigenenergies but also guarantees probability conservation. Interestingly, a wide class of non-Hermitian Hamiltonians can still show entirely real spectra. Among these are Hamiltonians respecting paritytime (PT) symmetry. Even though the Hermiticity of quantum observables was never in doubt, such concepts have motivated discussions on several fronts in physics, including quantum field theories, non-Hermitian Anderson models9 and open quantum systems, to mention a few. Although the impact of PT symmetry in these fields is still debated, it has been recently realized that optics can provide a fertile ground where PT-related notions can be implemented and experimentally investigated. In this letter we report the first observation of the behaviour of a PT optical coupled system that judiciously involves a complex index potential. We observe both spontaneous PT symmetry breaking and power oscillations violating leftright symmetry. Our results may pave the way towards a new class of PT-synthetic materials with intriguing and unexpected properties that rely on non-reciprocal light propagation and tailored transverse energy flow.

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Parity Violation
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Title: Observation of a Large Atomic Parity Violation Effect in Ytterbium
Authors: K. Tsigutkin, D. Dounas-Frazer, A. Family, J. E. Stalnaker, V. V. Yashchuk, D. Budker
(Version v3)

Atomic parity violation has been observed in the 6s^2 1S0 - 5d6s 3D1 408-nm forbidden transition of ytterbium. The parity-violating amplitude is found to be two orders of magnitude larger than in caesium, where the most precise experiments to date have been performed. This is in accordance with theoretical predictions and constitutes the largest atomic parity-violating amplitude yet observed. This also opens the way to future measurements of neutron skins and anapole moments by comparing parity-violating amplitudes for various isotopes and hyperfine components of the transition.

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