Difference between revisions of "FermiLab team member pages"

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"I know that this is the only group that will get an A." - Mr. Friedman

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Tim B.

Particle Adventure Reading: How do we know any of this?

To test theories, physicists put together experiments and use what they already know to find out what they do not know.

Up until 1909 - atoms= mushy, semi- permeable balls, with bits of charge strewn around them.

1909 – Rutherford experiment – Shot positive alpha particles at gold foil. Some of the alpha particles bounced off in different directions. Concluded that there must be small, dense, and positively charged objects, nuclei, in the gold foil

Now almost all particle physics experiments today use the same basic elements that Rutherford did: a beam, a target, and a detector

W and B Boson: The Weak Force

Will H.

Particle Adventure Reading: Other Points of Interest

There could be more than three physical dimensions that are so small that we cannot perceive them.

Antimatter

Antimatter? What is this, Star Trek?

All types of particles that we know have corresponding antiparticles. Antiparticles appear and act like their corresponding particles, except they have opposite particles. For example, a proton is charged positively while an antiproton is negative. The corresponding particles have the same mass and react the same way to gravity. When matter and antimatter collide, they form pure energy.

Antimatter seems to go against everything we know about the universe. The following is a "bubble chamber." The magnetic field affects the matter and antimatter differently. If you notice the two highlighted curls, the positron particles curl to the right while the electron particles curl to the left. This is antimatter and matter.

The usual symbol for an antiparticle is a bar over the corresponding particle symbol. For example, the "up quark" u has an "up antiquark" designated by , pronounced hUUUUe-bar.

Antimatter is said to be the most expensive substance in existence, with an estimated cost of $300 billion per milligram. That's a lot of antidollars!

History

In 1932, soon after Paul Dirac's prediction of positrons, Carl D. Anderson found that cosmic-ray collisions produced positrons in a cloud chamber, which is a particle detector in which moving electrons (or positrons) leave behind trails as they move through the gas.

Originally, positrons, because of the direction that their paths curled, (as shown in the previous visual) were mistaken for electrons traveling in the opposite direction.

The antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the UC Berkeley.

Nelly K.

Particle Adventure Reading: What is Fundamental?

WHAT IS FUNDAMENTAL Protons and neutrons are composed of quarks. Quarks and the electron are fundamental and are less than 10E-18 m in diameter. 99.99999999999% of atom is empty space. STANDARD MODEL THEORY: The fundamental particles are 6 quarks, 6 antiquarks, 6 leptons, 6 antileptons, and force carrier particles When a matter particle and antimatter particle meet, they annihilate into pure energy!

BUBBLE CHAMBER A bubble chamber is filled with protons. Momentum varies with radius: low momentum particles curve about a circle with a small radius and high momentum particles curve about a circle with a large radius Particles leave tracks due to their charges, so there are gaps in the tracks when only neutral particles pass through those areas. However, neutral particles can decay to form charged particles that are detected by a magnetic field. So, charge and momenta can be calculated from the tracks

The Fireworks of Elementary Particle Physics There are two types of quarks: up quarks (charge of +2/3) and down quarks (charge of -1/3) The composite particles that consist of quarks (such as neutron and proton) are called hadrons Protons: 2 up quarks and 1 down quark; neutron: 2 down quarks and 1 up quark

The Generations of Elementary Particles The structure of matter requires only 4 structural units: the up quark, the down quark, the electron, and the neutrino. Neutrino: electrically neutral particle that is essentially massless; by-product of neutron decay; along with electrons, they are called leptons. Leptons: electron, electron neutrino, muon, muon neutrino, tau, tau neutrino Quarks: Up, down, charm, strange, top, bottom Because every particle has an antiparticle, there are antileptons and antiquarks: 24, not 12, particles

Vail

Particle Adventure Reading: What Holds the Universe Together?

There are four fundamental interactions between particles that cause all forces.

‘‘What is the difference between force and interaction?’’ A force is the effect on a particle due to the presence of other particles. The interactions of a particle include all the forces that affect it, including decays and annihilations. Particles that carry interactions are called force carrier particles.

‘‘How do matter particles interact?’’ How can two objects affect one another without touching? What we normally think of as forces are actually the effects of force carrier particles on matter particles. A matter particle affected by that particular force absorbs or produces that force’s carrier particle. For instance, electrons and protons have electric charge, so they can produce and absorb the photon, which carries electromagnetic charge. Neutrinos have no electric charge, so they cannot absorb or produce photons. If a particle absorbs or produces a force carrier particle, the particle itself is affected.

‘‘What is the electromagnetic force?’’ Electromagnetic force causes like-charged things to repel and oppositely-charged things to attract. Friction and magnetism are caused by the electromagnetic force. For instance, the force that keeps you from falling through the floor is the electromagnetic force that causes the atoms in your feet and the floor to resist displacement. The carrier particle of the electromagnetic force is the photon. Photons of different energies span the electromagnetic spectrum of x-rays, visible light, radio waves, and so forth. Photons have zero mass and always travel at the speed of light, even in a vacuum.

‘’How do atoms form molecules?’’ Charged parts of one atom interact with the charged parts of another atom to bind them together, an effect called the residual electromagnetic force.

‘‘What binds the nucleus together?’’ Why doesn’t the repulsion force of protons cause the nucleus to blow apart? Quarks have electromagnetic charge and an unrelated charge called color charge. The force between color-charged particles is very strong, so it is called “strong.” The answer is that, in short, they don't call it the strong force for nothing. The strong force between the quarks in one proton and the quarks in another proton is strong enough to overwhelm the repulsive electromagnetic force. This is called the residual strong interaction, and it is what "glues" the nucleus together.

‘‘What are quarks and leptons?’’ There are six kinds of quarks and six kinds of leptons. But all the stable matter of the universe appears to be made of the two least-massive quarks (up quark and down quark), the least-massive charged lepton (the electron), and the neutrinos.

‘‘What are weak interactions?’’ Weak interactions are responsible for the decay of massive quarks and leptons into lighter quarks and leptons. When fundamental particles decay, the particle vanishes and is replaced by two or more different particles. Although the total of mass and energy is conserved, some of the original particle's mass is converted into kinetic energy, and the resulting particles always have less mass than the original particle that decayed. The only matter around us that is stable is made up of the smallest quarks and leptons, which cannot decay any further. When a quark or lepton changes type due to the weak interaction, it is said to change flavor. The carrier particles of the weak interactions are the W+, W-, and the Z particles. The W's are electrically charged and the Z is neutral. The Standard Model has united electromagnetic interactions and weak interactions into one unified interaction called electroweak. The weak and electromagnetic forces have essentially equal strengths. This is because the strengths of each interaction depend strongly on both the mass of the force carrier and the distance of the interaction. The difference between their observed strengths is due to the huge difference in mass between the W and Z particles, which are very massive, and the photon, which has no mass as far as we know.

‘‘How does gravity factor in to the situation?’’ Gravity is one of the fundamental interactions, but the gravity force carrier particle has not been found. Such a particle, however, is predicted to exist and may someday be found: the graviton. Fortunately, the effects of gravity are extremely tiny in most particle physics situations compared to the other three interactions, so theory and experiment can be compared without including gravity in the calculations. Thus, the Standard Model works without explaining gravity.

‘‘What is quantum physics?’’ One of the surprises of modern science is that atoms and sub-atomic particles do not behave like anything we see in the everyday world. They are not small balls that bounce around; they have wave properties. The Standard Model theory can mathematically describe all the characteristics and interactions that we see for these particles, but our everyday intuition will not help us on that tiny scale. Physicists use the word "quantum," which means "broken into increments or parcels," to describe the physics of very small particles.

A few of the important quantum numbers of particles are: Electric charge: Quarks may have 2/3 or 1/3 electron charges, but they only form composite particles with integer electric charge. All particles other than quarks have integer multiples of the electron's charge. Color charge: A quark carries one of three color charges and a gluon carries one of eight color-anticolor charges. All other particles are color neutral. Flavor: Flavor distinguishes quarks (and leptons) from one another. Spin: Large objects like planets or marbles may have angular momentum and a magnetic field because they spin. Since particles also to appear have their own angular momentum and tiny magnetic moments, physicists called this particle property spin. This is a misleading term since particles are not actually "spinning." We can use these quantum particle properties to categorize the particles we find.

‘‘What is the Pauli Exclusion Principle?’’ At one time, the predominant school of thought followed the Pauli Principle that no two particles in the same quantum state could exist in the same place at the same time. But it has been since discovered that a certain group of particles do not obey this principle. Particles that do obey the Pauli Exclusion Principle are called fermions, and those that do not are called bosons.

Particle Research: X Rays and Radioactivity

Hannah S.

Particle Adventure Reading: What is the world made of?

For every kind of matter there is an antimatter/antiparticle. Antimatter act the same as their corresponding matter, but have opposite charges. Gravity effects antimatter and matter the same way b/c gravity is not charged. When anti and matter meet they become pure energy. Electrons and Positrons come from photons splitting (they curl in different ways). Types of Quarks: Ups, Charms, and Tops charge:(2/3), Downs Stranges, and Bottoms charge: (-1/3). Quarks never exist alone, in groups called hadrons. Baryons: three quarks, Masons: One quark, one antiquarks. There are three charged and three uncharged Leptons. Charged: Electrons, muons, taus. Uncharged: neutrinos. Leptons decay into other smaller other leptons or quarks. lepton families: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino.lepton families: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino. Neutrino's tiny mass but huge numbers may contribute to total mass of the universe and affect its expansion.

Isaac Z.

Particle Adventure Reading: How do we experiment with tiny particles?

All particles behave like waves. If you increase the speed of a particle, you decrease the wavelength. Particle accelerators work by accelerating particle using magnetic fields (read Coulombs Force). To obtain particles to be used for acceleration, we can ionize hydrogen for protons, we can heat metal for electrons (same principle that allows old monitors and old TVs to work). To gain antiparticles, you fire an energetic particle at a target, then an antiparticle/particle pair is created. You can then separate the pair with a magnetic field (They have opposite charges, remember?). Here is an animation that is the easiest way to understand a particle accelerator:

Types of Collisions There are two ways to collide particles with an accelerator. You can shot the particles at a fixed target or you can cross two particle beams to create collisions between particles.

Types of Accelerators Linear Accelerators feed particles in one end and accelerate them out the other. Synchrotrons are built in a circle instead of a line.

Fixed Target Elements One target of particle accelerators is a fixed element. Instead of another beam of particles, the fixed element is placed in the path of the accelerated particle beam. Fixed elements can be solids, liquids, or gases, but they must be stationary. Rutherford's Gold Foil experiment is an example of a fixed target experiment. He accelerated alpha particles at the gold foil and monitored the foil.

Particle Beam Elements

Particle beam experiments are more interesting because they produce more massive particles. These experiments involve two accelerated beams. Since, there is much more momentum involved, there is much more mass/energy involved in the collisions. Remember, velocities don't add normally, so use the velocity composition formula instead.

Linear Accelerators vs. Circular Accelerators Linear Accelerators are used for fixed target experiments or as extraction paths for circular accelerators when the circular accelerator is being use for a fixed target experiment.

The straight part of Fermilab is the linear part of their circular accelerator.

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