Research Highlights

Performing high precision tests of the Standard Model with a low-cost experimental tabletop setup

In a recent publication in the Physical Review Letters, the group of Prof. Peter Rakitzis proposes a novel experimental test of the Standard Model, in the field of atomic parity non-conservation (PNC). Such atomic PNC experiments measure parity mixing of states from the exchange of neutral Z bosons between atomic electrons and quarks in the nucleus. Precise measurement of this mixing is sensitive to new physics at high energies. For example, the 0.35% precision measurement in Cs constrains the lower bound of extra Z’ bosons to 1.4TeV/c2. Improving such measurements to below 0.1% is very challenging but it can probe new physics at energies beyond the capabilities of the Large Hadron Collider at CERN. Furthermore, isotope and nuclear-spin-dependent atomic parity violation effects yield the nuclear anapole moment and provide information on the neutron distribution in the nucleus. To date, measurements of the nuclear anapole moment in Cs and Tl disagree with each other and with theoretical predictions, leaving an unresolved problem, requiring further experimental and theoretical work. Ongoing PNC experiments are performed on atomic systems with a large chain of isotopes (Yb, Fr, Ra+) and in one-valence electron systems where atomic structure calculations are expected to be performed with better than 1% precision (Fr, Ra+). However, these experiments are very difficult, having been ongoing for 15 years, and for radioactive Fr and Ra+ performed at particle colliders.

The group of Prof. Rakitzis is developing a novel PNC experiment in metastable Xe and Hg performed in a tabletop setup consisting of a high finesse optical cavity and a sealed Xe or Hg discharge lamp, with no moving parts or vacuum equipment. Xe and Hg together have 15 commercially available stable isotopes, and 4 with nuclear spin. They demonstrate new and robust signal reversal procedures associated with the well-known optical rotation technique. Their goal is to investigate whether these relatively simple and inexpensive experiments can be performed more quickly, and if so, allow atomic PNC experiments to be more accessible.

Reference: "Cavity-Enhanced Parity-Nonconserving Optical Rotation in Metastable Xe and Hg", by L. Bougas, G. E. Katsoprinakis, W. von Klitzing, J. Sapirstein, and T. P. Rakitzis, Phys. Rev. Lett. 108, 210801 (2012).

[Top] Proposed experimental setup, consisting of a high-finesse bowtie cavity with counter-propagating laser beams, containing a Xe or Hg discharge lamp, and followed by balanced polarimeters to measure the cavity-enhanced PNC polarization rotation of the laser beams.

[Bottom] Theoretical calculation of the expected experimental cavity- enhanced optical rotation signal, showing the characteristic antisymmetric PNC lineshape. The magnitude of the signal is proportional to the weak charge Qw.


June 2012


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