8.3 - The Particle Zoo Flashcards
What did Einstein suggest about matter and energy
Matter can appear where previously there was nothing but energy. Matter and energy are regularly interchanged in the universe according to his well known equation, E = mc^2.
Tell me about Einstein’s equation relating energy and mass
E = mc^2, in this equation, multiplying the mass of an object by the square of the speed of light gives the equivalent amount of energy.
Delta E = deltaM x c^2
Given a suitable quantity of energy, such as that in a gamma ray photon, particles can spontaneously appear and the energy disappears from existence. This is so commonplace in the universe that it should not surprise us. The reason it does is that these events only happen on a sub atomic scale, so we cannot detect them without complex machinery.
What’s an electron positron pair production
A gamma ray that converts into an electron and a positron (an anti electron has an identical mass to the electron). In momentum terms, it is just like an explosion. Initially only the photon existed so there was some linear momentum. Along this initial direction, their components of momentum must sum to the same total as the photon had. Perpendicular to the initial momentum, the electron and positron produced must have equal and opposite components of momentum so that in this direction it will still total zero afterwards.
In any reaction, the total combination of matter-energy must be conserved.
Should matter-energy be conserved?
Yes, in any reaction, the total combination of matter-energy must be conserved. If we add the energy equivalent of all matter particles with the energies, before and after the reaction, the numbers must be equal.
How is particle annihilation a source of energy
Just as matter can appear spontaneously through a conversion from energy, so energy can appear through the disappearance of mass. This is the source of energy in nuclear fission and fusion. In both reactions, the sum of the masses of all matter involved before the reaction is greater than the sum of all mass afterwards. This mass difference is converted into energy. In a nuclear power station we extract this energy as heat and use it to drive turbines to generate electricity.
What is annihilation
If a particle and its anti particle meet (anti particles are the antimatter versions of regular particles), they will spontaneously vanish from existence to be replaced by the equivalent energy: we call this interaction annihilation.
Could we use annihilation reactors to make power
It is not commonly suggested that annihilation reactors could be used as a power source on earth, as anti matter exists so rarely. Also, if we could find a supply of anti matter, it would annihilate on contact with any matter, which would most likely be before it reached the reaction chamber we had set up to extract the energy for conversion into electricity.
What can the electron volt unit be used for
Very small amounts of energy
What is one electronvolt (eV)
One electron-volt is the amount of energy gained by one electron when it is accelerated through a potential difference of one volt.
This is equivalent to a 1.6 x 10^-19 joules, so it is a very small amount of energy, even in particle physics terms. It is common for particles to have millions of even billions of electron volts. For this reason we often use MeV and GeV as units of energy in particle interactions.
What’s the atomic mass unit and what’s it used for
The atomic mass unit, u, is not an SI unit but is commonly used in particle interactions, as it is often easier to get to grips with 1 u = 1.67 x 10^-27 kg. As we know that energy and mass are connected by the equation E = mc^2,we can also have mass units which are measured E/c^2, such as MeV/c^2 and GeV/c^2.
1 u of mass is equivalent to about 931.5 MeV/c^2
What are other units for mass
As we know that energy and mass are connected by the equation E = mc^2,we can also have mass units which are measured E/c^2, such as MeV/c^2 and GeV/c^2.
1 u of mass is equivalent to about 931.5 MeV/c^2
No particle interactions can occur if they violate any of these conservation rules:
Momentum
Mass-energy
Charge
There are also other rules that must be obeyed, but these three are critical, as all particles involved will have some of each property.
Give me an example of what can be seen in a bubble chamber
A hydrogen bubble chamber that has an anti proton and proton collide in the chamber. The resulting tracks of various pairs of particles (pi+ and pi-, e+ and e-) which are created in the collision.
Define pair production
It’s the phenomenon in which a particle and its anti matter equivalent are both created simultaneously in a conversion from energy.
Define annihilation
The phenomenon in which a particle and its anti matter equivalent are both destroyed simultaneously in a conversion into energy which is carried away by force carrier particles, such as photons.
Define the electronvolt
The amount of energy an electron gains by passing through a voltage of 1V.
1eV = 1.6 x 10^-19 J
1MeV = 1.6 x 10^-13 J
What is the Standard model
After a century In which scientists rapidly discovered many sub-atomic particles, they have now established a theory for how these come together to build up the things we see around us. This theory is known as the standard model
As the idea of the atom as indivisible was swept aside by Rutherford and Thomson, so the idea of the proton and neutron as fundamental has also been overturned, what’s happened since
We have probed inside these two nucleons and discovered that each is constructed from smaller particles known as quarks.
Is the electron constructed by smaller parts
The electron has so far survived as being considered fundamental. However, it has two partners - similar types of particles - and each has a neutrino associated with it, forming a group of six fundamental particles known as leptons.
Tell me about quarks
Scientists like to see the universe as balanced, or symmetrical, we have now found that quarks are a group of six (like leptons)
Only the lightest two are found in protons and neutrons. The heavier quarks are found in rarer particles.
Tell me the distinction between the two groups: quarks and leptons
The two groups are distinct because quarks can undergo interactions via the strong nuclear force, whereas leptons do not feel the strong force.
What are the three generations of matter
It is the strong nuclear force that binds nucleons together in the nucleus. In each group of six (leptons and quarks) there are three pairs with a similar order of magnitude for mass, and these are known as the three generations of matter.
Ie first generation is up and down quarks and the electron neutrinos and electron leptons
Tell me about the family of leptons
Electron
Electron neutrino
Muon
Muon neutrino
Tau
Tau neutrino
^in order of generations of matter 1,2 and 3
Mass increases as you go down, neutrinos are lighter than the others
Tau, electron and muon have a charge -1
The family of leptons do not feel the strong nuclear force.
Tell me the characteristics of the first generation of matter for leptons
Consists of the electron and electron neutrino, the lightest leptons
Electron has symbol e^- , mass 0.511 MeV/c^2
Electron neutrino has symbol weird u(subscript e) no charge, mass 0(less than 2.2 x 10^-6)
Tell me about the second generation of matter for leptons
Consists of muon and muon neutrino
Muon has symbol mu (upside down h) charge -1, mass 106 MeV/c^2
Muon neutrino has symbol (weird u/v subscript upside down h) has charge 0, mass 0(less than 0.17 MeV/C^2
Tell me about the third generation of matter for leptons
Consists of tau and tau neutrino
Tau has symbol fancy T and charge -1, mass 1780 MeV/c^2 Tau neutrino (symbol weird u/v(subscript T) has charge 0 and mass 0 (less than 20 MeV/c^2)
What charge do the neutrinos have
0 and negligible mass (assume 0)
Tell me about the family of quarks
They are subject to the strong nuclear force.
As you go from 1st to 2nd to 3rd generation the mass of quarks increases
First generation - up and down quarks (u and d)
Second generation - strange and charm quarks (s and c)
Third generation - bottom and top quark (b and t)
Have charges +2/3 and -1/3
Each generation has one quark with each charge
The masses of particles in the standard model increase over…
generations
Tell me about the discovery of quarks and symmetry
Only the first three quarks - up, down and strange - were known from the middle part of the twentieth century, and the charm quark was discovered in 1974. The symmetry of the Standard model indicated to scientists that there were other particles they had never observed, which should exist - the bottom and top quark. Experiments were carried out to find these and the accelerator experiments at Fermilab discovered bottom in 1977 and top in 1995.
Current particle theory holds that all matter in the universe is constructed from combinations of…
Some of these 12 particles, and no others. The 6 leptons and 6 quarks - each also has an anti particle.
Tell me about anti-particles
Each of the 12 fundamental particles (leptons and quarks) also has an antiparticle. The anti particles have the same mass but all their other properties are opposite to those of the normal matter particle.
How do we write the symbol for an anti-particle
It is the same as the normal particle, with a bar above the symbol.
In a few cases, the anti particle notation treats it as a different particle on its own right and the bar may not be used. The positron (anti electron) does not use a bar but it is written as e^+
Define standard model
Standard model is the name given to the theory of all the fundamental particles and how they interact. This is the theory that currently has the strongest experimental evidence.
Define Quarks
Quarks are the six fundamental particles that interact with each other using the strong nuclear force (as well as all other forces)
Define leptons
Leptons are the six fundamental particles which do not interact using the strong nuclear force, only the other three fundamental forces.
