LHC Physics

From quarks to yet unknown particles, CERN continues to explore new frontiers in physics. Thanks to some of the most complex instruments ever made in a laboratory, Nature can reveal its inner secrets to the scientists.

Mass is the amount of material in an object. Newton showed us that weight is proportional to mass, and Einstein showed that energy is related to mass through the famous equation E = mc2. When it comes to elementary particles, physicists are dealing with a very fundamental question: where does the mass come from? 
Why do particles with no known structure have mass?

The answer may lie in the so-called Higgs mechanism. According to this theory, a medium - called the Higgs field - spreads through all the Universe at all times. Particles acquire their mass by interacting with this field, such that those that interact strongly are heavier than those having a weaker interaction. The Higgs boson is the manifestation of the field in the form of a particle. The LHC collision energy is enough to produce such a particle – if it exists.
Antimatter is routinely created in laboratories like CERN and in Nature when cosmic rays hit the atmosphere. Although matter and antimatter must have been produced in the same amounts at the time of the Big Bang, only matter seems to have survived in our Universe today.
  Where has all the Big Bang antimatter gone?

The explanation could be differences in the behaviour of matter and antimatter. Tiny experimental differences – the so-called CP violation effects – have already been observed but cannot, by themselves, explain the disappearance of antimatter. The LHC has some of the most advanced instruments to look for more differences between matter and antimatter.
It might seem that gravity should be the best known of the four fundamental forces. After all, we have our feet on the ground because of gravity! However, while physicists have found the particles associated with the other forces of Nature in their experiments, the particle of gravity, the graviton, has yet to be discovered. 
Could hidden dimensions disclose the graviton?

The Universe could have extra dimensions beyond the four dimensions we experience - three spatial dimensions plus time as the fourth. Hidden dimensions could be curled up to be so tiny that we are not aware of them. Some theories predict that high-energy particle collisions could create gravitons escaping into the extra dimensions. The LHC experiments could provide evidence for extra dimensions and allow the study of higher-dimensional gravitons.

Astronomical observations tell us that 96% of the Universe is unknown. About 70% is a new type of energy, the so-called dark energy, and 26% is dark matter. In contrast with ordinary matter, dark matter does not emit radiation and therefore cannot be detected directly by today’s instruments.

What is dark matter in the Universe made of?

Very massive particles, as yet undiscovered, could provide the explanation. One possibility is the neutralino, the lightest of the ‘supersymmetric’ particles that have been predicted in order to solve several puzzles of the Standard Model - the theory that embodies our current understanding of Nature. Thanks to the high energy available at the LHC, experiments could find supersymmetric particles and find evidence for the neutralino.


Quarks are the innermost known constituents of matter. Found in protons and neutrons, which, in turn, make up the atomic nucleus, they are confined within the particles they compose. At everyday temperatures they are never found free, thus making it very difficult for physicists to study them.
What are the inner properties of quarks?

In the high-energy collisions between beams of lead nuclei at the LHC, the temperature will exceed 1 billion times that of the centre of the Sun. In these conditions, the quarks are set free and matter exists as a sort of extremely hot, dense soup, called quark-gluon plasma. Physicists at the LHC are studying this state of matter that existed a few moments after the Big Bang, thus probing the basic properties of quarks. Experiments colliding protons at the highest LHC energies will be looking to see whether quarks themselves contain more fundamental constituents.

by CERN Bulletin