Particle Physics Intro

1. Particle Physics Intro

2. What’s Stuff Made Of…Really? All particles can be grouped into two categories: Fermions and Bosons BOSONS FERMIONS Things to know about Bosons: Particles that have integer spin # Can occupy the same state as another Things to know about Fermions: They have odd half- integer spin Hence obey the Pauli-Exclusion Principle Examples of Bosons: All the force-carriers (photons, gluons, W and Z) AND all particles comprised of an even # of fermions (like mesons) Examples of Fermions: Protons, neutrons, quarks electrons etc..

3. The fundamental particles are PARTICLES FERMIONS BOSONS LEPTONS FORCE CARRIERS QUARKS

4. Have net integer electric charges The fundamental particles are PARTICLES HADRONS FERMIONS BOSONS Have no net colour (ie. They are colour neutral) Particles made up of quarks are called LEPTONS FORCE CARRIERS QUARKS up , down charm, strange top, bottom NOTE: quarks have a fractional electric charge and have another distinguishing characteric called “colour” Note 2: Every particle in the standard model has an anti-particle. A charged anti-particle has all the same properties except it has the opposite charge of its matter “twin”. If the particle is not charged, the anti-particle has another quantum number that is opposite.

5. QUARKS Quarks come in different “flavors” and have fractional charges. Up: +2/3 Down: -1/3 Charm: +2/3 Strange: -1/3 Top: +2/3 Bottom: -1/3 Quarks are fermions and thus obey the Pauli Exclusion Principle no two particles in the same quantum state can exist in the same place at the same time However, the proton has two up quarks that would seem to be in the same state…

6. Quarks Physicists realized there must be a property that distinguishes these states: the called it color. We use this because when quarks combine in groups of three they form a color neutral particle. This is analogous to combining red, green and blue. The color charge of a quark has nothing to do with light. It is simply a way of distinguishing one from another. An example is the omega-minus particle which is comprised of 3 strange quarks. The distinguishing property must have 3 distinct values: red, green and blue. Each quark has an anti-quark with an opposite charge and the anti-color.

7. QUARKS Have net integer electric charges Make up Have no net colour (ie. They are colour neutral) HADRONS That are made up of three quarks That are made up of a quark-antiquark pair Mesons (which are bosons) Baryons (which are fermions) Have a baryon number of 0 Have a baryon number of 1 Ex: K- : s Examples include: Proton: uud Neutron: udd In all interactions, the baryon number is conserved The quarks of hadrons are held together by the strong force

8. The fundamental particles are PARTICLES FERMIONS BOSONS LEPTONS FORCE CARRIERS QUARKS gluons Make up W+, W- and Z0 HADRONS photons

9. FUNDAMENTAL PARTICLES BOSONS Are exchange particles that mediate the fundamental forces FORCE CARRIERS : mediate the STRONG FORCE between QUARKS. They also have color. The strong force increases with separation = no isolated color particles gluons W and Z :mediate the WEAK FORCE which is important in nuclear decays. photons : mediate the electromagnetic force between charged particles. These two forces have been unified into the ELECTROWEAK force. The difference in their ranges (weak = very short, EM = very long range) is simply due to the difference in their boson mass. W and Z are very massive whereas the photon is not. Gravitons: mediate GRAVITATIONAL FORCE between massive bodies

10. The fundamental particles are PARTICLES FERMIONS BOSONS LEPTONS FORCE CARRIERS QUARKS gluons Make up 3 flavors have charge of -1 3 flavors are neutral W and Z HADRONS photons

11. Leptons The electron is the best known lepton. The other two charged leptons are the muonand the tau. These are much more massive than the electron. The other leptons are neutrinos: They have no charge and very little mass and are very hard to find. 65 billion neutrinos pass through your fingernail every second! And maybe one or two collide with something in your nail – OVER YOUR ENTIRE LIFE!! The stable matter of the universe appears to be made of just the two least-massive quarks (up quark and down quark), the least-massive charged lepton (the electron), and the neutrinos.

12. Leptons The tau and muon lepton decay very quickly into lighter leptons. When a heavy lepton decays, one of the particles it decays into is always its corresponding neutrino. The other particles could be a quark and its antiquark, or another lepton and its antineutrino. Each family of leptons has a particular lepton number. The electron and its neutrino have an electron number of +1. Positronsand their antineutrinos have electron number -1, and all other particles have electron number 0. Muon number and tau number operate analogously with the other two lepton families. Family lepton number is conserved in all interactions.

13. More on Force Carriers Gluons are the exchange particles associated with the STRONG force. Gluons “stick” quarks together. Gluons are massless, neutral and have a spin of 1. They also carry color: but they carry two quantum numbers. They have 1 for color and the other for an anti-color. A gluon can be red and anti-blue, for instance. There are 8 gluons Ex: A green s quark emits a gluon and becomes a blue quark. State the flavor of the new quark and the colors of the emitted gluon. Gluons do not change the flavor via the strong interaction so the new quark is s as well. The gluon must carry green and antiblue.