Particle physics is beautiful! – the BELLE experiment

Belle detector (Image credit : KEK/Tokio Ohska)

Belle detector (Image credit : KEK/Tokio Ohska)

EPFL is studying particle physics within the framework of the “Belle” experiment, located in Japan. Certain measurements of B-mesons are easier to perform there than at CERN, and enable improvements in the precision of the standard model.

B-mesons – particles composed of quarks – constitute a kind of “open sesame” for basic physics. With their help, physicists are trying to understand the differences between matter and anti-matter. If these had been created in equal quantities at the time of the big bang, they would have annihilated each other. The surplus of matter is a result of the well-known violation of CP symmetry. However, in the standard model this phenomenon doesn’t suffice to explain the existing major predominance of matter. The Belle experiment uses the essential refining of current data to discover other sources of CP violation.

A painstaking task

Although not attaining the level of CERN, the energy of the collisions in the Belle experiment, between electrons and their antiparticles, has been adjusted to produce the maximum number of B-mesons. As a result, it’s now possible to create greater numbers of these heavy products, while retaining the advantage linked to the “cleanness” of the collision, which doesn’t produce the undesirable particles generated in more violent processes. Having a larger quantity of these mesons enables a reduction in the inaccuracies of the measurements, with the goal of better understanding their properties.

Remi Louvot has taken part in this long and fastidious project – it required nearly a month of measurements around the clock and six months of analysis – which is essential in determining whether there is a deviation of B-mesons compared with the standard model. “Theoretically, we can always rely on well-known factors, but it’s also necessary to understand with more precision the actual probabilities of the apparition and disintegration of B-mesons.” In order to notice a new mechanism of the violation of CP symmetry, it is essential that an unforeseen event can clearly stand out in the measurements.

A detailed examination of the relation between the probabilities of disintegrations now better understood, and those still to be examined, should open the way to no less than a better understanding of the mysteries surrounding the existence of the matter of the universe! Though this phase of the work will doubtless be hard work and not so exciting. According to Remi Louvot : “At Belle, we’re short of scientists to study this area, and the Bs-mesons are not well known.” However, the Belle experiments have demonstrated their usefulness, since they validate the theory of CP violation in the standard model, and earned the scientists the Nobel Prize for Physics in 2008.


Author: Nicolas Guérin
Source: EPFL