I NTRODUCTION TO P ARTICLE P HYSICS Isabel Baransky.

INTRODUCTION TO PARTICLE PHYSICSIsabel Baransky

AB

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•Sophomore at Columbia University's Engineering School (SEAS)

•Majoring in Applied Physics

• Minoring in Music

•Volunteer at multiple teaching organizations

• Peace by P.E.A.C.E

• Peer Health Exchange

• Let's Get Ready, Manhattan!

• Columbia Splash

ATOMSSubatomic Particles

LEPTONSElementary Particles

LEPTONS: ELECTRON

One of the building blocks of mass

Has a spin of ½, forcing it into the Pauli Exclusion Principle

Negative charge

Identical in mass but has a positive charge

If an electron and positron encounter, they will annihilate each other and produce two gamma rays (photons)

Electron Positron: Anti Particle

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When matter and antimatter ‘touch’, they immediately annihilate each other

For instance, electron and positron, or proton and antiproton

Two gamma rays are produced

At the beginning of the Big Bang, anti matter and matter was produced

For reasons unknown, matter “won” and now is the primary source of mass in the universe

PARTNER TO ELECTRON: NEUTRINO

Sibling of the electron Neutral charge and

almost zero mass Makes it incredibly

difficult to detect Produced in radioactive

decay of nuclei Neutron turns into a

proton by emitting a neutrino and an electron (beta decay)

“Fossil relic” from the Big Bang

Help reveal how fast the universe is expanding

Neutrinos constantly created in the core of the sun

Neutrino

BETA

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About 400 billion neutrinos from the Sun pass through each one of us each second

About 50 billion neutrinos from the ground (radioactive elements such as uranium) hit us each second

We emit about 400 neutrinos per second (yes, we are slightly radioactive1)

A neutrino can fly through a light-year of lead without hitting anything

Very difficult to detect as a result

LEPTONS: MUON AND TAU

Half life is 2.2 microseconds

Very massive Measuring the flux of

muons of cosmic ray origin at different heights above the earth is an important time dilation experiment in relativity.

Muons make up more than half of the cosmic radiation at sea level

3490 times more massive than the electron 17 times more

massive than the muon

Very unstable Half life of

2.96*10^-13 seconds

Muon Tau

QUARKSElementary Particles

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There are six quarks, but physicists usually talk about them in terms of three pairs: •up/down,•charm/strange•top/bottom. •For each of these quarks, there is a corresponding antiquark•Quarks have the unusual characteristic of having a fractional electric charge•Quarks also carry another type of charge called color charge

QUARKS: COLOR FORCE

The force between quarks

Dictated by gluons Replacement for the

strong force Strong force only

works in baryons Six colors: three for

quarks and three for anti quarks

Force does not decrease with distance

In fact, postulated to increase with distance

The quarks are like free particles within the confining boundary of the color force

Only experience the strong confining force when they begin to get too far apart

Color Force Over Distances

BARYONSSubatomic Particles

PARTICLES MADE OF QUARKS

Charge of positive one Slightly less massive

than a neutron Therefore more stable Half life of 10^32 years

Composed of two up quarks and one down quark

Held together in the nucleus with neutrons by the strong force

Neutral charge Composed of two down

quarks and an up quark .2% more massive than

a proton, making it more unstable A free neutron has a half

life of approximately 10.3 minutes

Decay of the neutron converts a down quark to an up quark using the weak force

Protons Neutrons

ELECTROMAGNETIC FORCEFundamental Force

ELEC

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A combination of the electric and magnetic force, unified under one theory

It is an exchange force

Carrier particle is the photon, a massless particle

Works over infinite distances

Follows the same inverse square law as gravity

More powerful than gravity, but over long distances it averages to 0

PHOTONS

A particle representing a quantum of light or electromagnetic radiation

Completely massless The infinite range of

the electromagnetic force is due to the rest mass of the photon

Has finite momentum Creates an issue

because it has no mass Can exert a force

GRAVITYFundamental Force

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Weakest of the four fundamental forces

Has the most influence over long distances

Carrier particle is hypothesized to be the graviton

Graviton is massless, similar to the photon

Infinite distance of influence

WEAK FORCEFundamental Force

WEA

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Dictated by the exchange of W and Z bosons

Weak force changes one flavor of quark into another

Vital for hydrogen burning in the core of the sun and for heavy nuclei build up

W and Z bosons are incredibly masssive, which means the weak force only works over very short distances (.1% of a proton)

Interacts with both quarks and leptons

STRONG FORCEFundamental Force

STRONG FORCE AND GLUONS

The strong force holds the particles in the nucleus together

The strong force between nucleons may be considered to be a residual color force

Basic exchange particle is the gluon which mediates the forces between quarks

DARK MATTERParticle Physics Standpoint

INTRODUCTION TO DARK MATTER In 1933, Fritz Zwicky measured the

mass of the Coma cluster of galaxies, one of the nearest clusters of galaxies outside of our local group

Zwicky’s technique was to measure the relative velocities of the galaxies in this cluster from their Doppler shift, use the virial theorem to infer the gravitational potential in which these galaxies were moving, and compute the mass that must generate the potential.

He found this mass to be 400 times the mass of the visible stars in galaxies in the cluster.

The observation was soon confirmed by similar measurements of the Virgo cluster

TYPES OF DARK MATTER

Speeds close to the speed of light

The very high speed of the particles would initially prevent the formation of a structure smaller than the supercluster of galaxies dividing up in galaxy cluster then in galaxies, then in smaller structures

The best candidate to constitute the hot dark matter is the neutrino

More massive and therefore slower than hot dark matter

The particles will go on a smaller distance and thus will erase the density's fluctuations on extents smaller than in the case of hot dark matter

The ordinary matter would then gather to form galaxies (starting from gas clouds and smaller structures), which themselves will gather in cluster, then supercluster

The candidates for cold dark matter are WIMP

Hot Dark Matter Cold Dark Matter

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Dark matter is based on the idea of the WIMP (weakly interacting massive particle)

A WIMP is a particle that is massive but stable

Can also be produced in pairs with a possible anti particle

Very low probability of interacting with matter

DETEC

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An experiment called XENON100 has been running deep underground at the Gran Sasso Laboratory in Italy. There, a vat filled with 137 pounds of liquid, ultra-pure xenon is protected by the 5,000 feet of ground above it, as well as layers of copper, polyethylene, lead and water, in an attempt to shield it from anything but WIMPS.

After collecting data for 13 months, scientists reported only two events that could have been collisions between WIMP particles and the xenon liquid. However, these two events could also have been caused by impacts from background particles, such as cosmic rays from space, that managed to bypass the detector's shields.