Name: ________________________
Particle Physics – Summary
for details see: http://www.particleadventure.org
“"Young man, if I could remember the names of these particles, I would have been a botanist!"
(Enrico Fermi to one of his students)

What is Fundamental?
People have come to realize that the matter of the world is made from a few fundamental building
blocks of nature. By fundamental building blocks we mean objects that are simple and
structureless -- not made of anything smaller. Even in ancient times, people sought to organize the
world around them into fundamental elements, such as earth, air, ____________, and
______________ – the four “elements” classified by ________________.
This idea was later replaced by the idea of ____________________ - The Greek word “atomos” means
________________________. But later on, the famous experiment conducted by ______________________ showed
that atoms had structure and were not just squishy balls. These experiments helped scientists determine
that atoms have a tiny but dense, positive nucleus and a cloud of negative electrons (e-). Because it
appeared small, solid, and dense, scientists originally thought that the nucleus was fundamental. Later,
they discovered that it was made of _________________________ which are positively charged, and
______________, which have no charge. Physicists have discovered that protons and neutrons are
composed of even smaller particles called _______________________. As far as we know, quarks are
like points in geometry. They're not made up of anything else. After extensively testing this theory,
scientists now suspect that quarks and the electron are __________________________.

What is the World Made Of?
Physicists have developed a theory called The Standard Model that explains what the world is and what holds it
together. It is a simple and comprehensive theory that explains all the hundreds of particles and complex interactions
with only:

6 ______________________________ (known as up, down, charm, strange, top and bottom)

6 ______________________________. The best-known one is the electron.

__________________________, like the photon.
All the known matter particles (e.g. molecules, protons, …) ________________________ of quarks and leptons,
and they __________________________ by exchanging force carrier particles.
For every type of matter particle we've found, there also exists a corresponding _________________ particle. They
look and behave just like their corresponding matter particles, except they have opposite ______________. For
instance, a proton is electrically positive whereas an antiproton is electrically negative. Gravity affects matter and
antimatter the same way because gravity is not a charged property and a matter particle has the same_______________
as its antiparticle. When a matter particle and antimatter particle meet, they _________________ into pure energy!
© Mag. Susanne Neumann – BRG XIV (susanne.neumann@brg14.at)
Name: ________________________

What Holds it Together?
The universe exists because the fundamental particles ______________. These interactions include attractive and
repulsive forces, decay, and annihilation. There are four fundamental interactions between particles, and all forces in the
world can be attributed to these four interactions. At a fundamental level, a force isn't just something that happens to
particles. It is a thing which is passed between two particles. It turns out that all interactions which affect matter
particles are due to an exchange of ____________________________, a different type of particle altogether. These
particles are like basketballs tossed between matter particles (which are like the basketball players). What we normally
think of as "forces" are actually the effects of force carrier particles on matter particles.
Name of the Force
is responsible e.g. for…
is carried by…
Insert the following words: photon, gravity, electromagnetic force, building of molecules, attraction between celestial
bodies, gluon, weak force, strong force, W/Z-boson, radioactive decay, building of protons and neutrons, graviton

Particle Decays And Annihilation
In nuclear decay, an _____________________ can split into smaller _______________. This makes sense: a bunch of
protons and neutrons divide into smaller bunches of protons and neutrons. But the decay of a fundamental particle
cannot mean splitting into its constituents, because "fundamental" means it has no constituents. Here, particle decay
refers to the _______________________ of a fundamental particle into other fundamental particles. This type of decay
is strange, because the end products are not pieces of the starting particle, but totally new particles.
Annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle. Since
_____________ and _________________must be conserved, the particles are not actually made into nothing, but rather
into new particles. During a low-energy annihilation, photon production is favored, since these particles have no
________________. However, high-energy particle colliders (e.g. the ________________) produce annihilations where
a wide variety of exotic heavy particles are created.

Unsolved Mysteries
The Standard Model is not complete; there are still many unanswered questions.

Why do we observe matter and almost no antimatter if we believe there is a symmetry between the two in the
universe?

What is this "dark matter" that we can't see that has visible gravitational effects in the cosmos?

Why can't the Standard Model predict a particle's mass – where is the famous _________________?

Are quarks and leptons actually fundamental, or made up of even more fundamental particles?

Why are there exactly three generations of quarks and leptons?

How does gravity fit into all of this?
© Mag. Susanne Neumann – BRG XIV (susanne.neumann@brg14.at)
Name: ________________________

How Do We Know Any Of This?
Rutherford's experiment set the tone for the realm of experimentation
in particle physics; in fact, almost all particle physics experiments
today use the same basic elements that Rutherford did:

A _________________
(in this case, the alpha particles)

A_________________
(the gold atoms in the foil)

A _________________
(the zinc sulfide screen)

How Do We Detect What’s Happening?
Quite often, physicists want to study massive, unstable particles that have only a fleeting existence (such as the very
massive top quark.) However, all that physicists have around them in the every day world are very low-mass particles.
How does one perform this amazing feat of using particles with lesser mass to
obtain particles of greater mass?
You know Albert Einstein's famous equation that____________________
where E is the energy, m is the mass, and c is the speed of light.
When a physicist wants to use particles with low mass to produce particles with greater mass, all she has to do is put the
low-mass particles into an ___________________, give them a lot of _____________ energy, and then collide them
together. During this collision, the particle's kinetic energy is converted into the formation of new massive particles. It
is through this process that we can create massive unstable particles and study their properties.

How Do We Experiment With Tiny Particles?
Basically, an accelerator takes a particle, speeds it up using ___________________ fields, and bashes the particle into a
target or other particles. Surrounding the collision point are ______________ that record the many pieces of the event.
Accelerators can be arranged to provide collisions of two types:
Fixed target: Shoot a particle at a fixed target.
Colliding beams: Two beams of particles are made to cross each other.
Accelerators are shaped in one of two ways:
Linacs: _____________ accelerators, in which the particle starts at one end and comes
out the other.
Synchrotrons: Accelerators built in a __________, in which the particle goes around and
around and around...
© Mag. Susanne Neumann – BRG XIV (susanne.neumann@brg14.at)