Nikhef is member of the LHCb experiment, one of the detectors at CERN’s Large Hadron Collider (LHC) in Geneva. Here, together with international colleagues, Nikhef scientists try to find answers to the many questions surrounding topics such as matter and anti-matter.
The LHC is a particle accelerator: it produces collisions between protons at extremely high energies, in order to study various known and unknown forms of matter among the fragments. These consist of quarks and leptons; the elementary building blocks of our Universe, and of their anti-matter partners.
Although collision experiments yield both matter particles and their anti-matter particles, the relative abundance of anti-matter in our Universe is found to be much less. How is it possible that the anti-matter particles have disappeared?
The LHCb experiment (where ‘b’ stands for ‘bottom’) studies this mystery by performing precision measurements on the decay of the so-called bottom-quark, or b-quark. The detector has been realized by a collaboration of 700 scientists from 50 different universities and research institutes in 15 countries.
The prevailing theory about the origin of our Universe is that of the Big Bang. 13.7 billion years ago, our Universe started from an immeasurably small and hot point: a singularity.
Shorty after the Big Bang there were equal amounts of matter and anti-matter. If a particle meets its anti-particle, they annihilate each other, resulting in a flash of energy. How is it possible that our Universe exists only of matter? Was there, just after the Big Bang, a mechanism preventing the matter and anti-matter from annihilating each other? Do other laws of nature apply to matter than to anti-matter? The solution probably lies in the latter: a slight asymmetry between particles and their anti-particles.
LHCb is designed to precisely identify the decay products of unstable particles and to accurately register their tracks. It studies the tiny differences between matter and anti-matter by using so-called bottom quarks and anti-bottom quarks. These particles are truly exotic, as they don’t exist in our Universe anymore, and can only be produced using a very powerful particle accelerator such as the LHC.
Does the b-quark always decay in the same way as the anti-b-quark does? Do the so-called forbidden b-quark processes occur anyway? Using the LHCb experiment, scientists try to unravel the mystery surrounding matter and anti-matter. The final goal is to understand what happened in the first nanosecond (1 billionth part of a second) of the Big Bang.
Nikhef played an important part by designing and building the VErtex LOcator (VELO) and the Outer Tracker (OT). These parts form the backbone of the LHCb detector; they measure the traces and vertices of the bottom decay products. Nikhef also developed that software that reconstructs the traces left behind by charged particles. In this way, decay events of unstable b particles can be detected online. A groundbreaking result, published in Nature, was the discovery of the forbidden decay of a b-particle to two muon particles.
Over the next years, Nikhef scientists will further analyze the research data in close collaboration with their international colleagues.