The Fundamental Forces
Positrons and Other
Mesons and the
Beginning of Particle
Classification of Particles
Strange Particles and
Finding Patterns in the
The Standard Model
g the Smallest System to
Understand the Largest
ANSWERS TO QUESTIONS
Strong Force—Mediated by gluons.
Electromagnetic Force—Mediated by photons.
Weak Force—Mediated by W
, and Z
Gravitational Force—Mediated by gravitons.
In the quark model, all hadrons are composed of smaller units called
quarks. Quarks have a fractional electric charge and a baryon
. There are 6 types of quarks: up, down, strange,
charmed, top, and bottom. Further, all
contain 3 quarks, and
contain one quark and one anti-quark.
to be fundamental particles.
Hadrons are massive particles with structure and size. There are two classes of hadron: mesons and
baryons. Hadrons are composed of quarks. Hadrons interact via the strong force.
Leptons are light particles with no structure or size. It is believed that leptons are fundamental
particles. Leptons interact via the weak force.
Baryons are heavy hadrons with spin
, are composed of three quarks, and have long
lifetimes. Mesons are light hadrons with spin 0 or 1, are composed of a quark and an antiquark, and
have short lifetimes.
Resonances are hadrons. They decay into strongly interacting particles such as protons, neutrons,
and pions, all of which are hadrons.
The baryon number of a proton or neutron is one. Since baryon number is conserved, the baryon
number of the kaon must be zero.
Yes, protons interact via the weak interaction; but the strong interaction predominates.
Decays by the weak interaction typically take 10
s or longer to occur. This is slow in particle
The decays of the muon, tau, charged pion, kaons, neutron, lambda, charged sigmas, xis, and omega
occur by the weak interaction. All have lifetimes longer than 10
s. Several produce neutrinos;
none produce photons. Several violate strangeness conservation.