Creation of Matter - a Matter of Energy

4Observing the fundamental processes in nature, particle physics aims at finding an answer to the basic question at the roots of nature: what is matter made of?. Physicists do this by trying to understand how particles interact. In order to give answers, they examine particles to see if they are elementary or composed by other, smaller components. From this procedure the researcher deduct a blueprint of nature. A way to accomplish the task is to collide small particles and examine the debris that are produced in these collisions. Starting with J. J. Thomsons discovery of the electron in 1897[Gri87] a whole zoo of particles has been detected and categorised (see table 2 for some examples. Quarks and leptons are fundamental particles[PRSZ95, p. 149]. Baryons or mesons which are both hadrons are built from quarks (up ($u$), down ($d$), strange ($s$), charm ($c$), bottom ($b$), top ($t$)). For every particle a corresponding anti-particle exists.). How these particles interact with each other is covered by laws of the elementary forces that we find in nature: the strong, the electromagnetic, the weak and the gravitational ones (see table 1 for an overview of forces and their carriers). Three of them are known to be mediated by exchange of particles, so called vector bosons[PRSZ95, p.149]. Each force is coupled to a specific kind of charge and particles can later be classified by which charge affects them. The electromagnetic and the weak force are manifestations of the same electroweak force. Particles that are sensitive to it are called leptons. Particle that are furthermore sensitive to the strong force are called hadrons.

The energies with which the particles in a collider are shot at each other have to be very high for several reasons: first, due to the coupling of energy and mass ($E=mc^2$), energy has to be high enough in order to produce new massive particles. There is a second reason for high energetic particle beams in colliders: The higher the energies are, the closer two particles can be brought together and interaction at very small distances be examined. This has been formulated in the de Broglie law $\lambda = h/p$, where $h$ is Planck's constant, $p$ is the particles momentum and $\lambda$ is the particles wavelength. The higher the momentum (and thus the energy), the shorter the wavelength, hence the smaller the distances that can be probed (see figure 5). The run for these goals gave this branch of physics the name high energy physics.