Physics Motivation

The main physics goal of LHC [4] is the discovery of the Higgs boson which is anticipated by the Standard Model. Theory only provides an upper limit for its mass of about $1\,\rm TeV$, while LHC will reach much higher energies. In the last period of LEP, when energies were pushed to the limits, a few possible Higgs candidates were observed suggesting a mass of about $114\,\rm GeV$. Due to the extended energy range of LHC, these particles will be undoubtedly confirmed and characterized if they exist as predicted by the Standard Model. Although 40 million bunch crossings occur per second in each of the four LHC experiments, the Higgs boson is expected to appear only about once every day, yet it is enough to accumulate good statistics.

Another motivation is the Charge-Parity (CP) Violation. At an early stage, the universe was dominated by energy. While expanding and cooling down, gradually matter and anti-matter formed and became dominant. However, it is not quite clear why today's world is entirely made of matter. The CP Violation implies a distinction of the weak force, which is responsible for decay, between matter and anti-matter. This could explain today's domination of matter. First reported in the 1960s, several experiments have measured the CP violation since. However, until now, it is only possible to observe a very small effect in the decay rates of Kaon particles. The results of these experiments differ considerably, and some even suggest no violation at all. LHC will enter a new energy range, allowing to study the CP violation on B-mesons, which will show a much more distinctive effect than Kaons if CP violation exists. The LHCb experiment will be dedicated to this study.

A large field of elementary particle physics is supersymmetry (SUSY). According to this theory, particles are said to have ``superpartners'' (sparticles). Since they have not been observed so far, SUSY must be a broken symmetry, which means that sparticles have masses different than their counterparts. The SUSY masses are expected in the $\rm TeV$ range, which makes them visible to LHC. Theory predicts at least five SUSY Higgs bosons and it can provide an explanation for the dark matter of the universe.

When colliding lead ions instead of protons, the energy density is much higher. Thus, it is expected to rebuild a very early stage of the universe called quark-gluon plasma, which may reveal different physical properties.