accelerator
A machine used to accelerate particles (for example,
electrons or
protons) to high speeds, and thus high energy (compared to their
rest mass energy). Then particles are usually driven to collide with other
particles. In this way Scientists can study the reactions which take
place, and therefore obtain information on
particles and
forces.
[close
the glossary]
annihilation
Process in which a particle meets
its corresponding antiparticle, and then the two particles destroy each
other. The total energy of the initial couple changes into the
rest mass of other particles and antiparticles and their kinetic
energy.
[close
the glossary]
antiparticle
It has the same mass as the particle, but opposite electric
charge and other
properties. Every particle has a corresponding antiparticle. Example: the
antiproton, antineutron and antielectron (or
positron) are the antiparticle of the proton, neutron and electron
respectively. When a particle meets its antiparticle the two particles
annihilate.
[close
the glossary]
antiproton
The
antiparticle of the proton. It has the same
mass as the proton, but
opposite electric charge.
[close
the glossary]
atom
The
smallest part of a simple substance (or element), which maintains
unaltered the properties of the simple substance. It is usually imagined
like a miniature solar system with a positive nucleus surrounded by
electrons.
[close
the glossary]
carrier particle
In particle
processes, the forces are described as due to the exchange of fundamental
particles, called "force carriers"; each type of force is associated with
a different type of carrier particle. The carrier particles are what, on
a microscopic level, transmit (or, as we say, "mediate") an interaction.
Example: the photon is the carrier particle of the electromagnetic
interaction.
[close
the glossary]
charge (electric charge)
Property of a
particle which determines its participation in the electromagnetic
interaction.
[close
the glossary]
C.E.R.N. (European
Council for Nuclear Research)
The Center, one of the most advanced for nuclear research, is located
near Geneva, Switzerland.
[close
the glossary]
collider
An accelerator in which beams of particles (such as protons and
antiprotons or electrons and positrons), travelling in opposite
directions, are driven to collide frontally together.
[close
the glossary]
conduction electron
Electron
that can move inside a conductor. When an electric field is applied to the
conductor, the electron movement gives rise to the phenomenon of
electric conduction (passage of current through a metal). In the
story: an electron is struck by a
photon, thus absorbs energy and
leaves the metal (Photoelectric effect).
[close
the glossary]
decay
Every
process in which a
particle disappears and another particle takes its place.
The sum of the masses of the produced particles is lower than the mass of
the initial particle. Examples: a neutron, isolated and at rest, decays
after about 15 minutes into a proton, an
electron and an electronic
antineutrino. Instead, the negative muon (mu-) decays, in two
millionths of a second, into an electron, a muonic neutrino and an
electronic antineutrino.
[close
the glossary]
electric field
The field associated with the electric force. It is united with the
magnetic field in the electromagnetic field.
[close
the glossary]
electromagnetic field
The field associated with the
electromagnetic force. This unites the electric
and magnetic field.
[close
the glossary]
electromagnetic interaction
A fundamental interaction of Nature. It unites the electric and magnetic
interactions. The interaction originates from the
electric charges and is mediated by the
photons. The electromagnetic
interaction binds
electrons and
nucleus to make an
atom. The force, which
binds atoms to make the molecules, is a "residual" electromagnetic force
shielded by the atomic electrons.
[close
the glossary]
electron
A fundamental particle, negatively charged. It is a last constituent
of matter and a stable particle. Note: in the story the
terms "young", "old", "girl-electron",
"woman-electron" and so on, attributed to the electrons,
are
pure fantasy! In Nature there is only one stable particle called an electron!
[close
the glossary]
electron microscope
A microscope that uses an electron beam instead of the
light (photons), for the lighting.
[close
the glossary]
elementary particle
The term
usually denotes the
last constituents (example:
quarks and
electrons), the carrier
particles (example:
photons and gluons),
and also the "composite" particles (example:protons and neutrons).
[close
the glossary]
force
In
dynamics, the physical agent capable of altering the state of motionlessness
or motion of a body.
[close
the glossary]
field
Region of space where a measurable physical greatness is measurable.
[close
the glossary]
fundamental interactions
They
are the
electromagnetic, strong,
weak and
gravitational interactions. The forces (the interactions) between
two particles are transmitted (or, as we say, mediated ) by
means of the exchange of a third virtual particle (virtual, since it
cannot be revealed). Each of the four interactions has its own virtual
particle or quantum. The quantum of the electromagnetic
interaction is the
photons. The strong interaction is mediated by gluons. The weak interaction
is transmitted by means of the W+,
W- and Z0 bosons. The quantum of the
gravitational interaction is the graviton (the latter not yet
directly observed).
[close
the glossary]
gamma
High energy photons emitted, for example, in the decay of atomic
nuclei or in
collisions between
particles.
[close
the glossary]
gluon
The carrier particle of the strong interaction.
[close
the glossary]
gravitational interaction
The
weakest of the four fundamental interactions. It's the interaction
between particles due to their mass/energy. The carrier particle
of the gravitational interaction is the graviton, not yet
experimentally observed.
[close
the glossary]
graviton
The hypothetical carrier particle of the
gravitational interaction. Not yet directly
observed.
[close
the glossary]
last constituents
The
particles for which a further subdivision is not possible at the present. They are the bottom step of the particle scale. For example:
quarks and
electrons are last constituents. Protons and
neutrons
are instead particles made of three quarks.
[close
the glossary]
magnetic field
The field
associated with magnetic force. It unites with the electric
field in the electromagnetic field.
[close
the glossary]
mass (rest mass)
The rest mass
(m) of a
particle is defined as the ratio between the energy E of
an isolated (free) particle at rest, divided by the square of the light
speed c (m= E/c2). When Scientists talk about "mass",
they always mean the "rest mass" m of the object in question.
[close
the glossary]
muon
An elementary particle, negatively charged (mu-).
A last constituent of matter. It's like the electron,
but about 200 times heavier. It decays
into an electron, a muonic neutrino and an
electronic antineutrino. Its meanlife is about two millionths of a second.
The corresponding antiparticle is the mu+.
[close
the glossary]
neutrino
A neutral
particle, having zero rest mass or very small (at the present time
Scientists are still investigating) and zero electric charge. There are
three kinds of neutrinos: electronic, muonic and tau.
[close
the glossary]
neutron
A neutral particle. It's made up of three
quarks. Neutrons together with protons make the atomic
nuclei.
[close
the glossary]
nucleus (atomic)
The central
part of an atom. It is made up of protons and
neutrons. It can be
consider the "sun" of the atom. In the nucleus is concentrated almost all
the mass of the atom.
[close
the glossary]
photon (electromagnetic field quantum)
The carrier particle
of the electromagnetic interaction. It's
electrically neutral. Note: in the story the light is imagined as being
made of many balls (!) which
represent the photons.
[close
the glossary]
positron
The
antiparticle of the electron. It has the same mass but opposite
charge of
the electron. When an electron meets a positron, they annihilate
giving rise to, in the simpler case, two energetic photons (gamma).
[close
the glossary]
proton
The nucleus of a hydrogen atom, it has a positive electric charge. It is
made up of three quarks. Together with the neutron it forms atomic nuclei.
[close
the glossary]
quantum
The smallest
discrete amount of any quantity. Examples: photons are the quanta
of the electromagnetic field.
The electron
charge is the quantum
of electricity.
[close
the glossary]
quark
A
last constituent of matter. For example, a
proton is formed
of three quarks. There are various kinds of quarks called up,
down, charm, strange, top and bottom.
[close
the glossary]
Special Relativity
Theory
developed by Einstein. It is based on two hypotheses: the light speed c
in the vacuum is constant, and the laws of Physics are the same
for observers in relative motion with constant speed. Special Relativity
supplies a new vision of time-space and provides
the possibility to convert energy into mass (and,
vice versa, mass into energy). Every system, with speed near to
that of light, has to be analysed with the formulae of relativistic
Mechanics rather than classic formulae.
[close
the glossary]
stable particle
Does not
decay. A particle is stable if there are no processes in which
the particle disappears and its place different particles appear.
Example: protons and
electrons are stable. Instead some particles live a
short mean life, then decay into other particles. Example: a
neutron, isolated and at rest,
decays after about 15 minutes into a proton, an
electron and an antineutrino.
[close
the glossary]
strong interaction
The strongest of the four fundamental interactions of Nature. It is
mediated by the gluons. It joins together
quarks to make protons and
neutrons, and, as "residual" strong force, unites protons
and neutrons to form the atomic
nuclei.
[close
the glossary]
subnuclear particle
Any particle that is small compared to the size of the atomic
nucleus.
The microscopic world is very rich in subnuclear particles with strange
names. Examples:
protons,
neutrons,
electrons,
muons,
neutrinos,
quarks and so on.
[close
the glossary]
W+, W-, Z0 boson
Carrier particles of the
weak interactions.
[close
the glossary]
weak interaction
A fundamental
interaction of Nature. It is known above all to be present in
decay processes. For example, it operates when a neutron decays into a
proton, an electron and an antineutrino. At ordinary energies, the
weak interaction is much weaker than the
electromagnetic and the strong one. At very high energy, the weak interaction is unified with the
electromagnetic one in the so called electroweak interaction.
[close
the glossary]
