Elephant in the room for the Nobel Prize in Physics!

On Tuesday it was announced that Makoto Kobayashi and Toshihide Maskawa have been awarded the Nobel Prize in Physics for 2008. The award is "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature." They share the prize with Yoichiro Nambu for his work on spontaneous symmetry breaking, a process vital to the derivation of the Higgs mechanism which gives particles mass in the standard model and which, as has been well publicised, is major part of the physics to be investigated with the LHC.

The work of Kobayashi and Maskawa concerns a slightly more obscure asymmetry in nature, so called CP violation. Essentially CP asymmetry reveals a subtle difference between the weak nuclear decays of some particles and their corresponding anti-particles and forms a cornerstone in the investigation of why the universe is made of matter and not anti-matter. It was first observed experimentally in the 1960s and at the time posed a theoretical conundrum. Kobayashi and Maskawa showed in the early 1970s that this effect could be incorporated into the standard model if there are at least 3 generations of quarks. This effectively predicted the yet to be discovered top and bottom quarks. Their work built on the flavour mixing formalism developed by the Italian Nicola Cabibbo and resulted in the so called CKM (Cabibbo-Kobayashi-Maskawa) matrix.


The ultimate test of the CKM matrix came this decade with the operation of the B Factories; BELLE in Japan and BaBar in the USA. These experiments produce pairs of B mesons (particle and anti-particle) and study their decays looking for the effects of CP violation predicted by Kobayashi and Maskawa. In 2001 both collaborations reported the first experimental observations of CP violation from B meson decays, completely in agreement with the CKM matrix formalism. They have since made scores of similar measurements all consistent with the model. Imperial College has been heavily involved with the BaBar experiment (named after the eponymous cartoon elephant who is also the experiment mascot) for the duration of it's running, which was completed earlier this year. We continue to work as part of the collaboration who are now analysing the final data set. Currently the Imperial group are looking at the effects of radiative penguin decays which can further constrain the elements of the CKM matrix.

It is the success of the CKM mechanism under intense experimental scrutiny which has made Kobayashi and Maskawa deserving winners of the 2008 Nobel Prize in physics.