Quark and gluon interactions

Particles produced in high energy proton-proton collisions at the CERN Large Hadron Collider are simulated. A proton is composed of three quarks and numerous gluons - the mediator of the strong interaction - which keep the quarks together. When two high energy protons collide, it is the constituents of the protons the quarks and gluons that interact.


The interaction occurs inside the two overlapping protons. The animations focus on the production of particles like top quarks and particles like the Z and the Higgs bosons. The production and also the decay of these massive particles occur inside the colliding protons before they have had time to separate. The proton remains often give rise to additional jets of particles (not shown in the Higgs, top and Z particle production animations).


1. Jets of particles

One of the most common interactions is the exchange of a gluon between a quark in one of the protons and a quark in the other proton. An exchange of a high energy gluon often gives rise to several jets of particles.
File: Particle jets


2. The Higgs particle

The Higgs particle is expected to be produced in collisions when a gluon from each of the protons merges in a high energy collision a gluon fusion. We know that the mass of the Higgs particle is large and therefore the two interacting gluons need to have high energy to be able to produce the Higgs particle. The Higgs particle will be produced very rarely, requiring a large number of particle collisions before one has a good chance to find it. The Higgs particle decays instantaneously, and can decay in several ways.
A particle with a mass around 126 GeV, compatible with being the Higgs particle, has recently been discovered by the ATLAS and CMS experiments at CERN.
File: Higgs → ZZ
File: Higgs → photons


3. The top quark

A pair of top quarks a top quark and an antitop quark - is expected to be produced in collisions when a gluon from each of the protons merges in a high energy collision a gluon fusion. The very massive top quarks will instantly start a sequence of decays into less and less massive quarks giving rise to a large number of quarks and leptons, like the electron and the muon. The b, c, s and u quarks that make up the complex decay sequence will combine with other quarks to form bound particle states, which can travel visible distances in the detector before they decay.
File: Top_quarks

4. The Z particle

The massive Z particle, having a mass close to hundred proton masses, is produced when a quark and an antiquark annihilate and will instantly decay into a quark and an antiquark or a lepton and an antilepton. The colliding high energy quark exists in the proton, but the antiquark has to be produced by one of the gluons in the proton converting to an antiquark and a quark. The quark-antiquark annihilation is the most likely reaction to produce a Z particle.
File: Z_particle