CERN researchers discover rare particle decay
A joint quest from the CMS and LHCb experiments of CERN has led to the discovery of one of the rarest particle decays in nature: the decay of a Bs
0 meson into two muons. The work, in which researchers from FOM institute Nikhef were also involved, was published on 13 May in Nature.
The Bs 0 meson is an unstable particle that consists of a so-called beauty antiquark and a strange quark. These particles destroy each other in the decay and in doing this they produce two muon particles.
In addition to this decay, the physicists have also found a hint of the comparable, but even rarer decay of the Bd 0 meson into two muons. The Bd 0 meson is similar to a Bs 0 particle but is composed of a beauty antiquark and a down quark.
Quantum mechanics
Due to their rarity both of these processes provide us with a deep insight into the virtual world of quantum mechanics. In this world new, unknown particles can spontaneously arise for a brief moment. However, during this short virtual existence these particles can subtly influence B mesons. As a result of this, the rare decays measured can possibly take place more or less often than physicists expect from calculations using the Standard Model – the standard theory that physicists use to describe particles and forces.
"The observed decay process of a Bs 0 particle into two muons is so rare that the chance of winning the lottery is 20 times greater", says Siim Tolk, a PhD student who has worked on this research at CERN. "The extent to which it occurs does, however, agree well with the expectation from the Standard Model. The observed hint of the even rarer process, the decay of a Bd 0 meson into two muons occurs slightly earlier than expected. However this does not mean that the current model is incorrect. We will need to carry out accurate measurements to make an assessment of that."
"The improvement of these measurements is one of the main objectives of the forthcoming LHC run and is vital for making a final pronouncement about the existence of new particles such as the so-called Z-prime boson, which was recently speculated about", says Antonio Pellegrino, senior researcher at Nikhef and closely involved in this measurement.
Contact information
Marcel Merk, +31 20 592 5107
Antonio Pellegrino, +31 20 592 5002
Reference
Observation of the rare Bs->mu+mu decay from the combined analysis of CMS and LHCb data, Nature, 13 May 2015. DOI: 10.1038/nature14474