Parity Violation has been studied extensively since its discovery in the 50's. It has now been observed in a wide variety of experiments at many energy scales and is well accounted for in the Standard Model. Yet Parity Violation continues be the the subject of much attention and effort. This is partly because there remain some fascinating loose ends related to its origin and precise structure, but current interest is mostly due to more practical motives as it has become a tool for uncovering clues about possible physics beyond the Standard Model.
At the relatively low energies at which we live and presently do experiments, the effects of physics at large energy scales is heavily suppressed.
In an atomic system, with energies of a few eV, the characteristic size of such an effect due to a new particle with a mass of 1 TeV seems to be hopelessly small compared to the natural size of a typical electromagnetic process.
In heavy atoms there are enhancements due to the size of the nucleus and relativistic electrons that increase this considerably.
This would still be very difficult to measure or interpret in a many body system as complicated as an atom, where it is currently a struggle to understand even just electromagnetic effects to a part in , and would be undetectable in practice if the effects of these new processes didn't also happen to have a fundamentally different character. One possible difference to exploit is parity violation.
The Weak sector of the Standard Model violates parity. In atoms this has been observed as a mixing between S and P opposite parity eigenstates through a exchange between the nucleus and a valence electron. Since Electromagnetism conserves parity, this mixing can be attributed solely to Weak processes and is proportional to a weak charge that can be assigned to the nucleus, with . Similarly, all the most promising extensions to the Standard Model naturally include new interactions that violate parity so they will have effects that appear as corrections to Weak sector parity violating observables. In this case the relative sizes of these new effects are given by the ratio of their masses to the already very high energy Weak scale.
Thus, a measurement of to 1% is sensitive to new physics at mass scales of about 1 TeV. This sort of precision is much more reasonable and once done, the interpretation becomes far more tractable. Here is the real power of studying parity violation. It allows for a differential measurement to sensitively test for possible classes of new physics, since the otherwise much larger QED effects that might mask new parity violating processes are effectively transparent to them.