# Standard Model of Matter: Bosons

This topic is part of the HSC Physics course of the section Deep Inside the Atom.

### HSC Physics Syllabus

• investigate the Standard Model of matter, including:

– quarks, and the quark composition hadrons
– leptons
– fundamental forces (ACSPH141, ACSPH142)
• analyse the evidence that suggests:
– that protons and neutrons are not fundamental particles
– the existence of subatomic particles other than protons, neutrons and electrons

### What are Bosons?

Bosons are fundamental particles that mediate the forces and interactions between quarks and leptons. Bosons and their fundamental forces differ in their relative strength and range over which they act.

### Gluons

Gluons are bosons that interact with quarks and hence hadrons as they consist of quarks. Gluons mediate the strong force or the strong nuclear force present in the nucleus of atoms.

Gluons were discovered in particle accelerators when high energy electron-positron annihilation produced a meson and a gluon.

### Photons

Photons are bosons that mediate the electromagnetic force. Photons act over an infinite range.

### W and Z Bosons

W bosons (W = weak) mediate the weak force (weak interactions). The weak force mediates the absorption and emission of neutrinos and antineutrinos such as those in radioactive decay and nuclear fusion.

Wbosons mediate beta-plus decay where an up quark in a proton is converted into a down quark, causing the proton to become a neutron. This process also produces a positron and electron neutrino.

W- bosons mediate beta-minus decay where a down quark in a neutron is converted into an up quark, causing the neutron to become a proton. This process also produces an electron and electron antineutrino.

Zo bosons (Z = zero electric charge) also mediate the weak force but they mediate the transfer of momentum between neutrinos and other matter. For example, high energy annihilation between electron and positron produces a Z boson which quickly decays to form a muon neutrino and muon antineutrino.

Unlike photons, W and Z bosons have mass.

The discoveries of W and Z bosons were made possible using particle accelerators.

### Higgs Boson

Higgs bosons are a group of force-mediating fundamental particles that are scalar in nature. This means they have no direction, no charge, no spin but have mass.

The existence of Higgs boson was predicted before its discovery in a particle accelerator (Large Hadron Collider) in 2013. The Higgs field (provided by the Higgs boson) accounts for the mass of W and Z bosons.

Previous section: Standard Model of Matter: Quarks and Leptons

Next section: Limitations of the Standard Model of Matter