physics: Particle Physics

All particles can be divided into which 2 categories?

1. fermions (purple & green) 2. bosons (red)

What are the 4 *fundamental forces* (fundamental interactions) in nature?

1. gravity 2. strong (nuclear) force 3. weak (nuclear) force 4. electromagnetism

How would the fundamental forces be arranged from weakest to strongest?

1. gravity 2. weak force 3. electromagnetism 4. strong force

What are 4 properties of particles that are relevant to how they interact with each other?

1. mass 2. charge (electric charge) 3. color (color charge) 4. spin

What are the *elementary bosons* that have been observed?

1. photons 2. gluons 3. W bosons 4. Z bosons (gravitons have not been observed)

What are the 2 types of *elementary fermions* (matter particles)?

1. quarks (purple) 2. leptons (green)

Which *generation* of fermions makes up stable matter?

1st generation (1st column). quarks: up & down leptons: electron & electron-neutrino.

What is a *boson*?

A "force carrier" particle (plays important role in fundamental forces). It has an integer spin (1, 2, 3, etc). It does not follow the exclusion principle (bosons with the same properties can be grouped together).

What is a *fermion*?

A "matter" particle (makes up matter). It has a half-integer spin (1/2, 3/2, etc). It follows the exclusion principle (fermions with the same properties can't be grouped together).

A *photon* is which kind of elementary particle?

A boson (force carrier) with zero mass.

What does *color neutral* mean?

A combination of color charges that results in no color ("white"), such as all 3 color charges (red, green, blue), or a color/anti-color combo. ex: red + green + blue = white ex: red + anti-red = white

What is a *neutrino*?

A fermion (lepton) particle with no charge (neutral) and almost no mass. Aka, the "ghost particle" because it's almost nothing. There are lots of them in the universe, but they're very hard to detect.

A *muon* is which kind of elementary particle?

A fermion (matter particle), specifically a lepton.

A *neutrino* is which kind of elementary particle?

A fermion (matter particle), specifically a lepton.

An *electron* is which kind of elementary particle?

A fermion (matter particle), specifically a lepton.

What is a *positron*?

A positive electron: same mass but a positive charge. An electron-positron pair is an example of a particle-antiparticle pair.

What is *color charge*?

A property that is related to the strong force the way electric charge is related to the electromagnetic force. It has nothing to do with the everyday meaning of color.

What is the *electroweak force*?

A unification of electromagnetism and the weak force. These are 2 versions of the same force.

What is an *antiparticle*?

An antimatter particle. A particle that has the same mass but the opposite charge of its partner "matter" particle.

What is a *tau*?

An unstable, charged lepton particle that is about 3000x more massive than an electron.

What is a *muon*?

An unstable, charged lepton particle that is more than 200x more massive than an electron.

What is *spin*?

Angular momentum, which for objects we can see is related to spinning, but for super-small things like electrons has very little to do with spinning. It's complicated and weird. Just think of spin as another property that can be described with values.

What is *matter*?

Anything that has mass and volume. Almost everything we observe in the universe is made of matter. In particle physics, it's more complicated, but this definition is good enough for now.

What are the 2 types of *hadrons*?

Baryons and mesons.

What is the difference between baryons and mesons?

Baryons are fermions (half-integer spin) made of 3 quarks. Mesons are bosons (integer spin) made of a quark and an antiquark.

Protons and neutrons are which kind of hadron?

Baryons. (fermions, half-integer spin, 3 quarks)

Why are *neutrinos* so hard to detect?

Because they're super tiny, travel near the speed of light, and hardly interact with anything.

How do fermions (matter particles) exchange energy with each other?

By exchanging bosons (force-carrier particles).

How do *color charged* particles interact with each other?

By exchanging gluons in strong interactions.

How do *electrically charged* particles interact with each other?

By exchanging photons in electromagnetic interactions.

Which property does the *strong force* act upon?

Color charge.

What are *hadrons*?

Composite particles made of quarks.

Which property does the *electromagnetic force* act upon?

Electric charge.

Which fundamental force is primarily responsible for atoms bonding to form molecules?

Electromagnetic force. The positive parts of atoms (protons) are attracted to negative parts (electrons) of neighboring atoms.

Friction is caused by which fundamental interaction?

Electromagnetism.

Which leptons are the most stable?

Electrons and the 3 kinds of neutrinos.

What is *antimatter*?

Every matter particle has a corresponding antimatter particle. Antimatter is like matter's equal and opposite partner that completes the pair.

What are *leptons*?

Fermion particles that do not have color, do exist on their own, and interact primarily via the electroweak force (electromagnetism and the weak force).

What are *quarks*?

Fermion particles that have color, do not exist on their own, and interact primarily via the strong force.

A *neutron* is made of which elementary particle?

Fermions (matter particle), specifically quarks. It's also a hadron, specifically a baryon.

A *proton* is made of which elementary particle?

Fermions (matter particle), specifically quarks. It's also a hadron, specifically a baryon.

Which boson carries the *strong force*?

Gluon.

Which bosons have high mass?

Gluons, W bosons, Z bosons.

Which boson (hypothetically) carries *gravity*?

Graviton (but it hasn't been discovered yet).

Which fundamental force is the *weakest*?

Gravity (gravitational force).

Which fundamental forces have an *infinite range*?

Gravity and electromagnetism.

Which fundamental interactions act on neutrinos?

Gravity and the weak force.

Planetary orbits are caused by which fundamental interaction?

Gravity.

Which fundamental force is not yet explained by The Standard Model?

Gravity. The gravity force carrier particle (graviton) is predicted but has not been found.

Which property does the *weak force* act upon?

Handedness and weak isospin. The weak force only acts on left-handed particles and right-handed antiparticles.

How is a boson's mass related to the range of the force it carries?

Long range forces have low mass carriers (bosons). ex: Photons are massless and carry the long-range electromagnetic force. Gluons are high mass and carry the short-range strong force.

Which property does the *gravitational force* act upon?

Mass.

Which is more abundant in the universe: matter or antimatter?

Matter. Antimatter is hardly observed in the natural universe. More commonly, antimatter is made artificially in particle accelerators, and even then, the antiparticles that are produced don't last long.

How are neutrinos different from their lepton partners (electron/electron neutrino, etc.)?

Neutrinos are neutral and have almost no mass, whereas their partners are charged and have a sizable mass.

Can *quarks* exist on their own?

No. Quarks only exist in groups and make up composite particles. Quarks combine with each other to form colorless (color neutral, "white") particles.

An *electron* is made of which elementary particle?

None (as far as we know). Electrons are elementary particles themselves.

Which boson carries the *electromagnetic force*?

Photon.

Which bosons are massless?

Photons. (And theoretically gravitons, which haven't been discovered yet.)

What are the types of *electrical charge*?

Positive (+) and negative (-). The same amount of positive and negative charge add up to a neutral (0) charge.

What is a *generation* in The Standard Model?

Quarks and leptons are grouped into pairs. A generation refers to the pairing. On a chart of The Standard Model, a generation is a column of fermions. For example, the 1st generation is up & down (fermions) and electron & electron neutrino (leptons).

Which elementary particle has the "flavors" *up*, *down*, *strange*, *charmed*, *top*, and *bottom*?

Quarks. Quarks have quirky "flavors". Each flavor refers to a particular set of values for electric charge, spin, etc.

What are the types of *color charge*?

Red, green, blue. Antiparticles have corresponding "anti" colors. (These "colors" are just labels and have nothing to do with everyday, visible color. They went with color because they needed something to describe 3 types of the same property that add up to something neutral.)

Hadrons interact primarily via which forces?

Strong force and weak force.

Which fundamental forces have a *very short range* (work only on subatomic particles)?

Strong force and weak force.

Which fundamental force is responsible for holding atomic nuclei together?

Strong force.

Which fundamental force is the *strongest*?

Strong force.

Nuclear bonding is caused by which fundamental interaction?

Strong interactions.

How does particle physics explain the fact that 2 objects can affect one another without touching?

The "invisible" force could be an exchange of force carrier particles (bosons).

What is *The Standard Model*?

The currently accepted explanation for how the building blocks of matter interact with each other via the fundamental forces. All matter is made of fundamental matter particles and all matter interactions are exchanges of force carrier particles.

At a fundamental level, what is a *force*?

The effect when force carrier particles (bosons) interact with matter particles (fermions).

What is the *weak force*?

The force responsible for radioactive decay and nuclear fusion. It changes the flavor of quarks.

What is the *strong force*?

The force that holds the nucleus together and is responsible for making protons and neutrons.

What is the *Higgs boson*?

The last particle of the Standard Model to be discovered. It helps explain how fundamental particles get mass.

What is an *electron*?

The most stable, least massive, charged lepton particle.

All stable matter appears to be made of which fermions (matter particles)?

The smallest quarks and leptons: 1. the least-massive quarks (up & down) 2. the least-massive charged lepton (electron) 3. the almost massless neutrinos

What happens when a particle and its antiparticle collide?

They will disappear (destroy each other) and produce electromagnetic energy in the form of gamma rays.

Which boson carries the *weak force*?

W and Z bosons.

Which fundamental force can change the flavor of a quark?

Weak force.

Which fundamental force is responsible for radioactive decay and lepton reactions?

Weak force.

Can *leptons* exist on their own (be isolated)?

Yes.

Can protons, electrons, and neutrons be broken down into even smaller particles?

Yes.