i ntroduction to p article p hysics isabel baransky
TRANSCRIPT
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INTRODUCTION TO PARTICLE PHYSICSIsabel Baransky
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AB
OU
T M
E
•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
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ATOMSSubatomic Particles
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LEPTONSElementary Particles
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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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AN
NH
ILIA
TIO
N: M
AT
TER
AN
D A
NTIM
AT
TER
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
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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
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BETA
DEC
AY
AN
D N
EU
TR
INO
S
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
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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
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QUARKSElementary Particles
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QU
AR
KS
AN
D C
HA
RG
E
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
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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
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BARYONSSubatomic Particles
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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
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ELECTROMAGNETIC FORCEFundamental Force
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ELEC
TR
OM
AG
NETIC
FO
RC
E A
ND
PH
OTO
NS
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
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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
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GRAVITYFundamental Force
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GR
AV
ITY
AN
D G
RA
VIT
ON
S
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
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WEAK FORCEFundamental Force
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WEA
K F
OR
CE A
ND
TH
E W
BO
SO
N
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
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STRONG FORCEFundamental Force
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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
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DARK MATTERParticle Physics Standpoint
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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
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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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GEN
ER
AL O
VER
VIE
W
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
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DETEC
TIN
G W
IMP
S
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.
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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.