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A hadron is a composite subatomic particle.Every hadron must fall into one of the two fundamental classes of particle, bosons and fermions. In particle physics, a hadron (/ ˈ h æ d r ɒ n / ⓘ; from Ancient Greek ἁδρός (hadrós) 'stout, thick') is a composite subatomic particle made of two or more quarks held together by the strong interaction.
Composite particles (such as hadrons, nuclei, and atoms) can be bosons or fermions depending on their constituents. Since bosons have integer spin and fermions odd half-integer spin, any composite particle made up of an even number of fermions is a boson. Composite bosons include: All mesons of every type
Composite particles (such as hadrons, nuclei, and atoms) can be bosons or fermions depending on their constituents. More precisely, because of the relation between spin and statistics, a particle containing an odd number of fermions is itself a fermion. It will have half-integer spin. Examples include the following:
The W bosons are known for their mediation in nuclear decay: The W − converts a neutron into a proton then decays into an electron and electron-antineutrino pair. The Z 0 does not convert particle flavor or charges, but rather changes momentum; it is the only mechanism for elastically scattering neutrinos.
The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction. Quarks cannot exist on their own but form hadrons. Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons.
Bosons are one of the two fundamental particles having integral spinclasses of particles, the other being fermions. Bosons are characterized by Bose–Einstein statistics and all have integer spins. Bosons may be either elementary, like photons and gluons, or composite, like mesons. According to the Standard Model, the elementary bosons are:
The other members of the hadron family are the baryons—subatomic particles composed of three quarks. The main difference between mesons and baryons is that mesons have integer spin (thus are bosons) while baryons are fermions (half-integer spin). Because mesons are bosons, the Pauli exclusion principle does not apply to them.
Because quarks have a spin 1 / 2 , the difference in quark number between mesons and baryons results in conventional two-quark mesons being bosons, whereas baryons are fermions. Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa.