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INVASIONS IN

PARTICLE PHYSICS

Compton Lectures Autumn 2001M. Spiropulu

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LECTURE 1LECTURE 1

What is Particle Physics about - The scientific method - Photons: the quanta of light - Electrons - The Electromagnetic Spectrum -High energies and elementary particles

outline

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PARTICLE PHYSICS (PP)

orElementary Particle Physics (EPP)

or High Energy Physics (HEP)

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One of the physical sciences that attempts to answer the following questions:

We seek fundamental fundamental answers to these questions in that the answers are given in terms of physical principles physical principles that cannot be explained by “deeper” principlesthat cannot be explained by “deeper” principles

What is the world made of?What is the world made of?

How it did come about?How it did come about?

How does it work?How does it work?

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What will we know if we find the fundamental answersto these questions?

The dynamics of space and time

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PP questions (in other words)

Is there a small numbersmall number of distinct objectsdistinct objects from which the universe is made?

Is there a small numbersmall number of simple rulessimple rules to explain howthese objects mesh together to make up everything?

What kind of observationsobservations in what kind of laboratorieslaboratoriescan we make to study the above?

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In more wordsIn more words

Particle physics tries to answer questions about (the origin and nature of) the universe

by studying the objects that are found in itstudying the objects that are found in it,

bystudying their interactionsstudying their interactions

by means ofby means ofarranging experimentallyexperimentally the objects (and their interactions)

in such ways that the ultimately “primitive”, ultimately elementary, smaller objects (and ultimately simple interactions)

are discovered or revealed or deduced.

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This is almost like someone trying to learn This is almost like someone trying to learn how to play chess, by studying the shapes of how to play chess, by studying the shapes of the pieces and the ways in which they move the pieces and the ways in which they move

across the board !across the board !

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How do we go about getting the answers?How do we go about getting the answers?

1 or 21 or 2: Make a guessguess and compute physical consequences

2 or 12 or 1: Observe/measureObserve/measure

33: CompareCompare the consequences of the guess with the measurements

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Breakdown: Breakdown: What is the world made of?What is the world made of?

The “visible” matter in the universe is made of electrons (e)electrons (e)up (u) quarksup (u) quarksdown (d) quarksdown (d) quarks

5-10 times more than this, is we don’t know 5-10 times more than this, is we don’t know what; we call it what; we call it

“dark matter”

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Timeline: What is the world made of?Timeline: What is the world made of?

Anaxagoras : changes in matter are due to different orderings of changes in matter are due to different orderings of indivisible particles.indivisible particles.

Empedocles : reduced these indivisible particles into four elements: earth, air, fire, and water.

Democritus : developed the theory that the universe consists of empty space and an (almost) infinite number of indivisible particles which differ from each other in form, position, and arrangement. All matter is made of indivisible particles called atoms.atoms.

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Archimedes (287-212 BC) provided the foundations of hydrostatics. Eratosthenis (276-196 BC) measured the circumference of the earth.Roger Bacon (1214-92) taught that in order to learn the secrets of nature we must first observe the method by which people can develop deductive theories is observation, i.e. using evidence from the natural world. Nicolaus Copernicus (1473-1543) claimed that the Sun and not the Earth is at rest in the center of the Universe.

1550-1898: Galileo Galilei, Johannes Kepler, Isaac Newton, Thomas Young, Michael Faraday, Joseph Henry, James Clerk Maxwell, William Röntgen, Marie Curie, Joseph Thompson

Timeline: How does it work?Timeline: How does it work?

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Timeline: The first elementary particles

The particle of light (or photon*, or (gamma)) & the electron ee--

* “phos” = light ( in greek)

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Characterize the photon ()

It does not stand stillIt goes with the speed of light c (300,000Km/s)

It does not have massIt does not have electric charge but it is responsible for charged particles “feeling” each other (good or bad feelings, attract or

repel)It has spin* one (s=1, and is called a boson* because of this)

* commit the words to memory; we will come back to spin

Is it a particle or is it a wave? Is it a particle or is it a wave?

“interaction” “mediates”

Photon is the “quantum” of light“quantum” of light : Photons of a particular color (frequency) come with energy:

Photon Energy = Planck’s quantum constant (h) * frequency

Photon is the “quantum” of light“quantum” of light : Photons of a particular color (frequency) come with energy:

Photon Energy = Planck’s quantum constant (h) * frequency

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Waves Interfere

Photoelectric Effect

Double Slit Experiment

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Characterize the e-

It is a massive elementary particleIt has negative electric charge

It has spin* 1/2 (s=1/2, and is called a fermion* because of this)It is found in the atom

An accelerating electron emits electromagnetic radiation

* commit the words to memory; we will come back to spin

Is it a particle or is it a wave? Is it a particle or is it a wave?

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Bohr’s atom and de Broglie’s electron waves

The atoms can exist only in discrete quantum states separated by finite energy differences; when in these quantum states the atoms do not radiate set of allowed orbits for the electrons around the nucleous.

WHEN AN ELECTRON WHEN AN ELECTRON MAKES A TRANSITIONMAKES A TRANSITIONFROM ONE ORBIT TO THE FROM ONE ORBIT TO THE OTHER IT EMITS LIGHTOTHER IT EMITS LIGHT

The atoms can exist only in discrete quantum states separated by finite energy differences; when in these quantum states the atoms do not radiate set of allowed orbits for the electrons around the nucleous.

WHEN AN ELECTRON WHEN AN ELECTRON MAKES A TRANSITIONMAKES A TRANSITIONFROM ONE ORBIT TO THE FROM ONE ORBIT TO THE OTHER IT EMITS LIGHTOTHER IT EMITS LIGHT

The wavelength of a particle wave is inversely proportional to its momentum, the constant of proportionality being Planck’s contant (h): Allowed orbits are explained as containing an integral number of the de Broglie’s wavelengths.

The wavelength of a particle wave is inversely proportional to its momentum, the constant of proportionality being Planck’s contant (h): Allowed orbits are explained as containing an integral number of the de Broglie’s wavelengths.

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To all practical intents and purpose a physics system such as a singleTo all practical intents and purpose a physics system such as a singleelectron, or a photon or an atom exists by some form of observation.electron, or a photon or an atom exists by some form of observation.[“Concerning that of which we can not speak we must pass over in[“Concerning that of which we can not speak we must pass over insilence” Wittgenstein. “If you don’t see, don’t say” Feynman ]silence” Wittgenstein. “If you don’t see, don’t say” Feynman ]

Any act of observation on a quantum system will disturb it. Any act of observation on a quantum system will disturb it.

Electrons and photons are neither particles nor wavesElectrons and photons are neither particles nor waves; ; they are they are ““quantum fields”. Depending on the experiment, we see them quantum fields”. Depending on the experiment, we see them either as waves or as particles.either as waves or as particles.

There is a There is a wave-function that reflects a particle’s localization that reflects a particle’s localization

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Aspects of light : the Electromagnetic SpectrumAspects of light : the Electromagnetic Spectrum

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Lowest frequencies (longest wavelengths) of the electromagnetic spectrum.

An interesting thought is that some form of extra-terrestrial intelligence could send us messages with radio waves that can be received by radio telescopes.

Lowest frequencies (longest wavelengths) of the electromagnetic spectrum.

An interesting thought is that some form of extra-terrestrial intelligence could send us messages with radio waves that can be received by radio telescopes.

Look at the SETI projectLook at the SETI project

Radio wavesRadio waves

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MicrowavesMicrowavesMicrowaves have wavelength between roughly 30 centimeters and 1 millimeter

Microwaves have wavelength between roughly 30 centimeters and 1 millimeter

The cosmic microwave background is the afterglow radiation left over from the hot Big Bang. Its temperature is extremely uniform all over the sky. However, tiny temperature variations or fluctuations (at the part per million level) can offer great insight into the origin, evolution, and content of the universe.

The cosmic microwave background is the afterglow radiation left over from the hot Big Bang. Its temperature is extremely uniform all over the sky. However, tiny temperature variations or fluctuations (at the part per million level) can offer great insight into the origin, evolution, and content of the universe.

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Infrared radiation comprises wavelengths between 1 millimeter and 750 nanometers (750 millionths of a millimeter). We cannot see it, but we can feel it as heat.

Infrared light is emitted when the atoms and molecules in an object oscillate. IR observations have to be made from telescopes in high, dry places, away from clouds that block the IR.

Infrared radiation comprises wavelengths between 1 millimeter and 750 nanometers (750 millionths of a millimeter). We cannot see it, but we can feel it as heat.

Infrared light is emitted when the atoms and molecules in an object oscillate. IR observations have to be made from telescopes in high, dry places, away from clouds that block the IR.

The atmosheree filters out most of the electromagnetic radiation from the sun except for portion of the radio waves and the region around visible light. The sun emits almost half of its energy in just that segment of the spectrum that we are able to see.

Water is transparent to visible light too. That is the reason why light can pass through our eyeballs, whose chief constituent is water, to reach the retina.

The atmosheree filters out most of the electromagnetic radiation from the sun except for portion of the radio waves and the region around visible light. The sun emits almost half of its energy in just that segment of the spectrum that we are able to see.

Water is transparent to visible light too. That is the reason why light can pass through our eyeballs, whose chief constituent is water, to reach the retina.

How you can measure IR temperature at home

How you can measure IR temperature at home

Infrared and VisibleInfrared and Visible

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Gamma raysGamma rays form the short-wavelength end form the short-wavelength end of the electromagnetic spectrum. They have of the electromagnetic spectrum. They have the highest frequencies and energies. the highest frequencies and energies. Gamma rays are created in radioactive Gamma rays are created in radioactive processes in atomic nuclei and when matter processes in atomic nuclei and when matter and antimatter annihilate each other and and antimatter annihilate each other and create pure energy.create pure energy.

Gamma raysGamma rays form the short-wavelength end form the short-wavelength end of the electromagnetic spectrum. They have of the electromagnetic spectrum. They have the highest frequencies and energies. the highest frequencies and energies. Gamma rays are created in radioactive Gamma rays are created in radioactive processes in atomic nuclei and when matter processes in atomic nuclei and when matter and antimatter annihilate each other and and antimatter annihilate each other and create pure energy.create pure energy.

Ultraviolate radiation covers wavelengths between 400 nanometers (4 millionths of a millimeter) and 10 nanometers.

Ultraviolate radiation covers wavelengths between 400 nanometers (4 millionths of a millimeter) and 10 nanometers.

X-rays have wavelengths between 10 nanometers* and 0.01 nanometers. They are created when the inner electrons in an atom change their orbit around the nucleus and lose energy in the process.

X-rays have wavelengths between 10 nanometers* and 0.01 nanometers. They are created when the inner electrons in an atom change their orbit around the nucleus and lose energy in the process.

*1nm = 10-9 m

Ultaviolate X-rays Gamma RaysUltaviolate X-rays Gamma Rays

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radioradio infraredinfrared opticaloptical

X-rayX-rayX-ray+opticalX-ray+optical

Eta Carinae PicturesPictures

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The smaller the wavelength the smaller the structure the wave will resolve (compare the optical microscope to the X-ray).

Particles with very large momentum (high energy particles)have extremely small wavelengths and can probe subatomicdistances: High Energy Particle Accelerators serve as super-microscopes.

The higher the energy the closer particles can come to each other and thus the smaller details of their structure can become important in determining how they bounce off each other.

The higher energy available, the heaviest particles can be produced in a collision (E=mc 2).

Particle Physics - High Energy PhysicsParticle Physics - High Energy Physics