Fundamental Particles and Interations

This page is an extract from CPEP

The "Standard Model" of particle physics describes the fundamental interactions (forces) between elementary particles. It includes the theory of strong interactions (quantum chromodynamics or QCD) and the unified theory of weak and electromagnetic interactions (electroweak). Gravity is not included in the theory though it is shown in the table below for completeness.

Table of fundamental forces. 52k gif
In the 'Standard Model' the mediators of the forces are called BOSONS.

Chart of BOSONS. 64k gif

The fundamental constituents of matter are named FERMIONS. All matter is built from these particles.

Chart of FERMIONS. 78k gif

Top quark discovered (Fermilab news release)

The electron, up-quark and down-quark form the fundamental constituents atoms.

Structure within the Atom. 116k gif

Quarks combined in pairs (bosonic hadrons) or triplets (fermionic hadrons) form a variety of particles (the Hadrons). The common proton and neutron belong to this family. More exotic particles are also formed:

bosonic HADRONS 32k gif fermionic HADRONS 29k gif

The energy unit of particle physics is the electron volt (eV), the energy gained by one electron in crossing a potential difference of one volt. Masses are given in GeV/c2. (Remember E = mc2 ), where 1 GeV = 109 eV = 1.60 * 10-10 joule. The mass of the proton is 0.938 GeV/c2 = 1.67*10-27 kg

Neutron Decay. 27k gif

Figure (left) : A neutron decays to a proton, an electron, and an antineutrino via a virtual (mediating) W boson. This is neutron beta decay.

eta_c to piplus K0 Kminus. 33k gif Figure (right) : The c and cbar quarks in an eta_c meson annihilate into virtual gluons. Quark pair production in the gluon cloud sometimes gives a pi+, K0, and K- as the final state.

eplus eminus to Dplus Dminus. 29k gif

Figure (left) : An electron and positron (antielectron) colliding at high energy can annihilate to produce D+ and D- mesons via a virtual Z boson or a virtual photon.