Particle Physics With Sanjay 630mod2

Particle physics is the study of what everything is made of

Particle Physicists study the fundamental particles that make up all of matter, and how they interact with each other. Everything around us is made up of these fundamental building blocks of nature.

In the early 1900's it was believed that atoms were fundamental; they were thought to be the smallest part of nature and were not made up of anything smaller

Soon thereafter, experiments were done to see if this truly was the case. It was discovered that atoms were not fundamental at all, but were made up of two components: a positively charged nucleus surrounded by a cloud of negative electrons.

Then the nucleus was probed to see if it was fundamental, but it too was discovered to be made up of something smaller; positive protons and neutral neutrons bound together with the cloud of electrons still surrounding it.

After that these protons and neutrons were found it was time to see if they were fundamental. It was discovered that they were made up of smaller particles called "quarks", which today are believed to be truly fundamental, along with electrons. Furthermore, electrons belong to a family of fundamental particles, which are called "leptons". Quarks and leptons, along with the forces that allow them to interact, are arranged in a nice neat theory named the standard model

The Standard Model

The Standard Model is a theoretical picture that describes how the different elementary particles are organized and how they interact with each other along with the different forces. The elementary particles are split up into two families, namely the quarks and the leptons. Both of these families consist of six particles, split into three generations, with the first generation being the lightest, and the third the heaviest. Furthermore, there are four different force carrying particles which lead to the interactions between particles. The table below shows this all a little bit more clearly.

An interesting thing that has been discovered about matter particles, is that each one has a corresponding antiparticle. The term "anti" may be a bit deceiving, as it is still real matter. The only difference between a particle and it's antiparticle is that an antiparticle has the opposite electrical charge. Think of it as a mirror image. Here left and right are the only things to reverse when looking in the mirror. Similarly, in the particle world, charge is what reverses when looking in the "mirror". It's mass, spin and most (quarks have something called color charge which is also changed in the "mirror") other properties are the same.

In particle physics, Antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles. For example, an antielectron (a positron, an electron with a positive charge) and an antiproton (a proton with a negative charge) could form an antihydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom. Furthermore, mixing matter and antimatter would lead to the annihilation of both in the same way that mixing antiparticles and particles does, thus giving rise to high-energy photons or other particle– antiparticle pairs

• A positron is the antimatter equivalent of an electron. Like the electron, the positron has a spin of ½, and an extremely low mass (about 1/1836 of a proton). The only differences are its charge, which is positive rather than negative (hence the name), and its prevalence in the universe, which is much lower than that of the electron. Being antimatter, if a positron comes in contact with conventional matter, it explodes in a shower of pure energy, bombarding everything in the vicinity

Antimatter • Almost every object observable from the Earth seems to be made of matter rather than antimatter. Many scientists believe that this preponderance of matter over antimatter (known as baryon asymmetry) is the result of an imbalance in the production of matter and antimatter particles in the early universe, in a process called baryogenesis

When particles of matter and antimatter collide they annihilate each other, creating conditions like those that might have existed in the first fractions of a

This is where high energy accelerators come in. In head-on collisions between high-energy particles and their antiparticles, pure energy is created in "little bangs" when the particles and their antiparticles annihilate each other and disappear. This energy is then free to reappear as pairs of fundamental particles, e.g., a quark- antiquark pair, or an electron-positron pair, etc. Now electrons and their positron antiparticles can be observed as two distinct particles. But quarks and antiquarks behave somewhat like two ends of a string — you can cut the string and have two separate strings but you can never separate a string into two distinct "ends". Free quarks cannot be observed!

Just as in the Big Bang, if we can manage to make high enough temperatures, we can create some pairs of quarks & anti-quarks, by the conversion of energy into matter. (Particles & anti-particles have to be created in pairs to balance

Quarks are a type of elementary particle and are major constituents of matter. Quarks combine to form composite particles called HADRONS, the best-known of which are e.g. protons and neutrons They are the only particles in the standard models to experience the strong interactions addition to the other three fundamental interactions fundamental interactions, also known as fundamental forces.

There are six types of quarks (plus their six antiquarks), which are coupled into three pairs. They are the up-down, the charm-strange, and the top-bottom (sometimes known as truth-beauty). Another interesting fact about quarks is that you can never find one by itself, as they are always with other quarks arranged to form a composite particle. The name for these composite particles is "hadrons". Quarks, like protons and electrons, have electric charge. However, their electric charges are fractional charges, either 2/3 or -1/3 (-2/3 and 1/3 for antiquarks), and they always arrange to form particles with an integer charge (ie. -1, 0, 1, 2...).

Flavor

Mass (GeV/c2 )

Elect ric Char ge (e)

u

up

0.004

+2/3

d

down

0.08

-1/3

c

charm

1.5

+2/3

s

strange

0.15

-1/3

t

top

176

+2/3

b

bottom

4.7

-1/3

Because quarks join with each other to form particles with integer charge, not every kind of combination of quarks is possible. There are two basic types of hadrons. 1) baryons, which are composed of three quarks, and 2) mesons which are made up of a quark and an antiquark. Two examples of a baryon are the neutron and the proton. And of mesons +kaon, -kaon, pion

The proton is composed of two up quarks and one down quark. As you can see, when the charges from the individual quarks are added up, you arrive at the familiar charge of +1 for the proton

1proton charge= 2u+1d= 2*2/3 + 1*(-1/3)=+1

Quarks

Mass (GeV/c2)

Elect ric Char ge (e)

u

up

0.004

+2/3

d

down

0.08

-1/3

The neutron is made up of two down quarks and one up quark. Again, adding the charges from the quarks up, we arrive at zero.

An example of a meson is the pion. It is composed of an up quark and a down antiquark. Because mesons are a combination of particle and antiparticle, they tend to be very unstable and decay very quickly

Like quarks, there are six types of leptons, and again, in three pairs. Electron - neutrino, muon - neutrino, and tau - neutrino (these three neutrino's are different from each other). The electron, muon, and tau each carry a negative charge, whereas the three neutrinos carry no charge. Leptons, unlike quarks,exist by themselves, and, like all particles, have a corresponding antiparticle.

There are four fundamental forces in nature.

1. Electromagnetism 2. Strong 3. Weak 4. Gravity These four forces all occur because of the exchange of force carrier

particles

Well, pretend you want to knock a bird out of a tree 100 yards away. You must exert a force to do this, but the darn bird is out of your reach. So, you take out a pitching wedge and a golf ball, take a swing. If you're good enough, you will successfully exert a force on the bird and knock it down from its perch, with the golf ball being the force carrier. Not all types of matter though are affected by all force carrying particles. For example, the proton and electron are affected by the force carrier particle of the electromagnetic force, the photon.

Electromagnetism is one of the two forces that dominate our everyday lives (the other one being gravity). The words you are reading radiating from your monitor are a result of electromagnetism Theelectromagnetic force acts between all particles that have electricharge. It is attractive for oppositely charged particles, and repulsive for particles of the same charge F =kQq/r^2 Interaction b/t electron and electron

Interaction b/t electron and proton

The electromagnetic force gets weaker and weaker the further apart the particles are, but it's range is infinite. The carrier of this force is the photon, most commonly observed as light. Another thing the electromagnetic force is responsible for is binding atoms together to form molecules. Although most atoms have a net neutral charge, the positive charge from within one atom can attract a negative charge within another atom, thus binding the two atoms together. This is called the "residual electromagnetic force".

This is the force between quarks particles which is very powerful, thus it is called the "strong force". The strong force is strictly an attractive force which acts between nucleons (protons and neutrons). It attracts any combination of protons and neutrons. i.e.. neutrons attract neutrons, protons attract neutrons... This is the force that overcomes the repulsive force within an atom due to the electromagnetic force and holds the nucleus together. The strong force actually acts between quarks, and it's the residual strong force (similar to the residual electromagnetic force) that causes nucleons to attract. The carrier of this force is the gluon (( elementary expressions of quark interaction, and are indirectly involved with the binding of protons and neutrons together in atomic nuclei. ))

All the stable matter in the universe appears to be made up of one type of lepton (the electron) and two quarks (the up and down), which compose the neutron and the proton. However, there have been six types of each that have been predicted and observed, The reason why we don't observe these more massive quarks and leptons is due to the weak force. It is the weak force that causes massive leptons and quarks to decay into lighter leptons and quarks. The weak forces have weak strength as 10^9 times less than that of the strong nuclear force. The term nuclear indicates that it is a short-range force, limited to distances smaller than an atomic nucleus

Gravity acts between all particles that have mass. Mass will attract other mass with a force that gets weaker as the distance between them gets larger. Gravity is responsible for the large scale structure of the universe. Here's a pretty picture of a galaxy, which, of course, is held together by gravity. Although gravity appears to be a very powerful force, when it comes to things on smaller scales, like tiny particles, can be ignored because of its weakness. The carrier of the gravitational force is the gravitron. Although it has never been observed in experiment, it is strongly believed to exist.

F = GMm/r^2

Modern versions of Rutherford's table-top experiment on the scattering of alpha particles occupy many square kilometers of land, with massive and costly apparatus in underground tunnels tens of kilometers long. These are the particle accelerators that speed protons, antiprotons, electrons, or positrons to near the speed of light and then make

In an accelerator, focusing magnets and bending magnets guide the beam of particles around a ring. (Only a few of the bending magnets are shown here). High

them collide head-on with each other or with

frequency microwave (RF) cavities

Beyond this, the Universe holds at least two dark secrets: Dark Matter and Dark Energy! The total amount of luminous matter (e.g., stars, etc.) is not enough to explain the total observed gravitational behavior of galaxies and clusters of galaxies. Some form of mysterious Dark Matter has to be found. Below we will see how new kinds of particles may be discovered that fit the description. Recent

A Hubble Telescope photograph of galaxies deep in Universe

We believe that the Universe started off with a "Big Bang", with enormously high energy and temperature concentrated in an infinitesimally small volume. The Universe immediately started to expand at a furious rate and some of the energy was converted into pairs of particles and antiparticles with mass—

leaving just a tiny fraction of matter to carry on in the Universe. As the Universe expanded rapidly, in about a hundredth of a second it cooled to a "temperature“ of about 100 billion degrees, and quarks began to clump together into protons and neutrons which swirled around with electrons, neutrinos and photons in a grand soup of particles. From this point on, there were no free quarks to be found. In the next three minutes or so, the Universe

light nuclei such as deuterium, helium and lithium. After about three hundred thousand years, the Universe cooled enough (to a few thousand degrees) to allow the free electrons to become bound to light nuclei and thus formed the first atom. Free photons and neutrinos continue to stream

Presented by Sanjay Kumar