CONTENTS
1. INTRODUCTION… 3
2. HISTORY OF THE UNIVERSE… 4
3. QUANTUM PARTICLES…
8
3. 1. Quarks… 8
3.
1. 1. Up and Down Quarks… 9
3. 1. 2.
The Strange Quark… 10
3. 1. 3.
The Charm Quark… 11
3. 1. 4. The Top Quark… 11
3.
1. 5. The Bottom Quark… 12
3. 1. 6.
Color Force… 12
3. 2. Leptons…
13
3. 2. 1. Electrones and Positrons… 14
3. 2.
2. Muon… 15
3. 2. 3. Tau…
15
3. 2. 4. Neutrinos… 16
4. CONCLUSION…
18
5. BIBLIOGRAPHY… 19
INTRODUCTION
What do we know about the small particles of matters? A lot of people will say that the smallest particle in the space is “Atom”, but is it true? No. The modern quantum particle theory says that there are smaller particles called quarks, leptons, photons and gravitons. Quarks are the particles, which forms in the atom. They are the smallest particles known which forms nucleus of atoms.
There are six quarks and two of them makes protons and neutrons.
Leptons are the negative charged particles. There are three leptons and three neutrino of these three leptons. The most common lepton is electron and its neutrino, electron neutrino.
Before having details about these two particles, we must know a little about the big bang and the beginning of universe.
2.
HISTORY OF THE UNIVERSE
Formation of the modern universe was occured step by step and I am going to present it by subscripts. First of all we don’t know anything about how the big bang occured but we can make some predictions about how it was occured after the big bang. The most popular theory is below.
10-43 seconds after the Big Bang
Quantum Gravity
Electromagnetic force, weak and strong nuclear forces are staying as a whole. (Big Union) Universe starts becoming larger from an origin which has endless energy.
t
Big union is getting broken and the effects of strong nuclear force and electroweak force become visible.
t = 10-35 s, 1027 K (1016 GeV, 10-32 m):
Universe’s length multiplied in every 10-32 s and swelling stops at the end of 10-32 th second. Now the length of the universe is 1018 m at that time the strong nuclear force becomes separated. There becomes a ratio of 1, 000, 000999. 999 between matter and anti-matter but the temperature is too high for them to union so they stay in a plasma of quark-gluon.
10-10 seconds after the Big Bang
Electroweak Period
Electromagnetic force and weak nuclear force are separated from each other.
t = 10-10 s, 1015 K (100 GeV, 10-18 m): Universe is getting larger. Temperature is getting lower by the laws of thermodynamic. At last weak nuclear force freezes and becomes a free force. So the four main force of the nature has become released. Quarks and anti-quarks terminated each other and there remained a little matter which is left.
W and Z bosons, which carries electroweak force, were decayed. Also big and unstable particles vanishes.
10-4 seconds after the Big Bang
Protons and Neutrons
Protons and neutrons are formed by the combination of quarks.
t = 10-4 s, 1013 K (1 GeV, 10-16 m):
Part of the universe that we can spectate is now at the length of our solar system. Remained quarks forms protons and neutrons.
t = 1 s, 1010 K (1 MeV, 10-15 m):
Neutrino separate.
Charge less particles ‘neutrinos’ become neut r. Electrones and positrons terminate each other and some electrones remained. Protons are more stable particles than neutrons, so the ratio of Proton Neutron becomes 75: 25 from 50: 50.
100 seconds after the Big Bang
Formation of nucleus.
Protons and neutrons come together to form Helium nuclei.
t = 3 d, 109 K (0. 1) MeV, 1012 m):
Now the temperature is low enough for nuclei to be formed. Deuterium, helium, litium nuclei, which are relatively heavy, sour neutrons and the remaining neutrons decay in 1000 seconds. The ratio between proton and neutron becomes 87: 13. The universe is like the center of a star or the core of a hydrogen bomb.
Electrones are in the state of gas.
300, 000 years after the Big Bang
Atoms and Light
Universe becomes transparent and fills with light.
t = 300, 000 y’yl, 6000 K (0. 5 eV, 10-10 m):
Negative charged electrons attach to positive charged nuclei.
At last hydrogen, helium and litium atoms are formed. The electrons, which were moving freely in the universe now become at teched to nuclei, so now photons can move freely. This makes the universe transparent.
1, 000, 000, 000 years after the Big Bang
Formation of Galaxies
Galaxies start appearing.
t = 109 years, 18 K:
Little differences in mass densities make a good condition for galaxy formation. Nucleus synthesis (formation of heavy nuclei from carbon till iron) starts with thermonuclear reactions in the core of stars.
This period takes a very long time. Some elements’ Formation takes a billion year and some elements are synthesized in supernova explosions.
1, 500, 000, 000 years after the Big Bang
Today
Human being is curious about where did he come from.
t = 1. 5 X 109 years, 3 K:
Chemical periods come free atoms together by sharing electrons and formed molecules. These structures also come together and form organic molecules like DNA’s and the combination of these organic molecules make the first living creature.
These molecules come together in different combinations and form different creatures by natural selection (G”urdilek ek; Hoof t 44).
When we look into our universe’s history we can see nearly all of the importance of small particles. Here there is a chart shows the whole steps (Figure 1) (G”urdilek 44).
Figure 1: Shows the big bang step by step.
Time flows from left to right.
3. QUANTUM PARTICLES:
The general name of the particles I am going to present are called quantum particles. You see below all kinds of particles (Table 1).
Table 1: Particle concepts.
As far as we know today quarks and leptons are the smallest building blocks of matter
3.
1. QUARKS
The name “quark” was taken by Murray Gell-Mann from the book “Finnegan’s Wake” by James Joyce. The line “Three quarks for Muster Mark… .” appears in the fanciful book. Gell-Mann received the 1969 Nobel Prize for his work in classifying elementary particles (Akat 70)
A quark is a fundamental particle which possesses both electric charge and ‘strong’ charge. They combine in groups of two or three to form composite objects (called mesons and baryons, respectively), held together by the strong force.
Protons and neutrons are familiar examples of such composite objects both are made up of three quarks (Akat 71).
The quarks come in six different species (physicists call them ‘flavors’), each of which have a unique mass. The two lightest, unimaginatively called ‘up’ and ‘down’ quarks, combine to form protons and neutrons. The heavier quarks aren’t found in nature and have so far only been observed in particle accelerators (Brent 3; Alt ” yn, screen 2).
Quark Symbol Spin Charge Baryon
Number S C B T Mass
Up
U 1/2 +2/3 1/3 0 0 0 0 360 MeV
Down
D 1/2 -1/3 1/3 0 0 0 0 360 MeV
Charm
C 1/2 +2/3 1/3 0 +1 0 0 1500 MeV
Strange
S 1/2 -1/3 1/3 -1 0 0 0 540 MeV
Top
T 1/2 +2/3 1/3 0 0 0 +1 174 GeV
Bottom
B 1/2 -1/3 1/3 0 0 +1 0 5 GeV
Table 2: Properties of Quarks (Nave 1).
3.
1. 1. UP AND DOWN QUARKS
The up and down quarks are the most common and least massive quarks, being the constituents of protons and neutrons and thus of most ordinary matter (Nave screen 1) (Table 3).
Table 3: The up and down quarks are east massive quarks, being the constituents of protons and neutrons.
3. 1.
2. THE STRANGE QUARK
In 1947 during a study of cosmic ray interactions, a product of a proton collision with a nucleus was found to live for much longer time than expected: 10-10 seconds instead of the expected 10-23 seconds! This particle was named the lambda particle () and the property which caused it to live so long was dubbed “strangeness” and that name stuck to be the name of one of the quarks from which the lambda particle is constructed. The lambda is a baryon which is made up of three quarks: an up, a down and a strange quark.
The shorter lifetime of 10-23 seconds was expected because the lambda as a baryon participates in the strong interaction, and that usually leads to such very short lifetimes. The long observed lifetime helped develop a new conservation law for such decays called the “conservation of strangeness.” The presence of a strange quark in a particle is denoted by a quantum number S = -1.
Particle decay by the strong or electromagnetic interactions preserve the strangeness quantum number.
The decay process for the lambda particle must violate that rule, since there is no lighter particle which contains a strange quark – so the strange quark must be transformed to another quark in the process. That can only occur by the weak interaction, and that leads to a much longer lifetime. The decay processes show that strangeness is not conserved (Table 4):
Table 4: The decay processes show that strangeness is not conserved:
The omega-minus, a baryon composed of three strange quarks, is a classic example of the need for the property called “color” in describing particles.
Since quarks are fermions with spin 1/2, they must obey the Pauli exclusion principle and cannot exist in identical states. So with three strange quarks, the property which distinguishes them must be capable of at least three distinct values (Nave screen 1).
The omega-minus, a baryon composed of three strange quarks, is a classic example of the need for the property called “color” in describing particles. Since quarks are fermions with spin 1/2, they must obey the Pauli exclusion principle and cannot exist in identical states. So with three strange quarks, the property which distinguishes them must be capable of at least three distinct values.
Table 5: The omega-minus, a baryon composed of three strange quarks
3.
1. 3. THE CHARM QUARK
In 1974 a meson called the J/Psi particle was discovered. With a mass of 3100 MeV, over three times that of the proton, this particle was the first example of another quark, called the charm quark. The J/Psi is made up of a charm-anti charm quark pair.
The lightest meson which contains a charm quark is the D meson.
It provides interesting examples of decay since the charm quark must be transformed into a strange quark by the weak interaction in order for it to decay.
One baryon with a charm quark is a called a lambda with symbol. It has a composition udc and a mass of 2281 MeV/c^2 (Nave 1).
3. 1.
4. THE TOP QUARK
Convincing evidence for the observation of the top quark was reported by fermilab ‘s tevatron facility in april 1995. The evidence was found in the collision products of 0. 9 tev protons with equally energetic antiprotons in the proton-antiproton collider. the evidence involved analysis of trillions of 1.
8 tev proton-antiproton collisions. the collider detector facility group had found 56 top candidates over a predicted background of 23 and the d 0 group found 17 events over a predicted background of 3. 8. the value for the top quark mass from the combined data of the two groups after the completion of the run was 174. 3 +/- 5. 1 gev.
this is over 180 times the mass of a proton and about twice the mass of the next heaviest fundamental particle, the z 0 vector boson at about 93 gev (Nave 1).
The interaction is envisioned as follows:
3. 1. 5- THE BOTTOM QUARK
In 1977, an experimental group at Fermilab led by Leon Lederman discovered a new resonance at 9.
4 GeV/c^2 which was interpreted as a bottom-antibottom quark pair and called the Upsilon meson. From this experiment, the mass of the bottom quark is implied to be about 5 GeV/c^2. The reaction being studied was
where N was a copper or platinum nucleus. The spectrometer had a muon-pair mass resolution of about 2%, which allowed them to measure an excess of events at 9. 4 GeV/c^2. This resonance has been subsequently studied at other accelerators with a detailed investigation of the bound states of the bottom-antibottom meson (Nave screen 1).
3. 1. 6. COLOR CHARGE
A property of quarks labeled color is an essential part of the quark model. The force between quarks is called the color force (Nave 2)…
Quarks and gluons are color-charged particles.
Just as electrically-charged particles interact by exchanging photons in electromagnetic interactions, color-charged particles exchange gluons in strong interactions. When two quarks are close to one another, they exchange gluons and create a very strong color force field that binds the quarks together. The force field gets stronger as the quarks get further apart. Quarks constantly change their color charges as they exchange gluons with other quarks (The particle data group, screen 3)…
How does color charge work?
There are three color charges and three corresponding anticolor (complementary color) charges. Each quark has one of the three color charges and
each anti quark has one of the three anticolor charges.
Just as a mix of red, green, and blue light yields white light, in a baryon a combination of “red,”green,” and “blue” color charges is color neutral, and in an antibaryon “antired,”anti green,” and “anti blue” is also color neutral. Mesons are color neutral because they carry combinations such as “red” and “antired.” (Figure 2).
Figure 2: Colors of quarks and Anti-Colors of Anti-Quarks.
Because gluon-emission and -absorption always changes color, and -in addition – color is a conserved quantity – gluons can be thought of as carrying a color and an anticolor charge.
Since there are nine possible color-anticolor combinations we might expect nine different gluon charges, but the mathematics works out such that there are only eight combinations. Unfortunately, there is no intuitive explanation for this result (The particle data group, screen 3)…
Important Disclaimer:
“Color charge” has nothing to do with the visible colors, it is just a convenient naming convention for a mathematical system physicists developed to explain their observations about quarks in hadrons (The particle data group, screen 3).
3.
2. LEPTONS
Leptons and quarks are the elementary particles of matter. There are six leptons in the present structure, the electron, muon, and tau particles and their associated neutrinos The different varieties of the elementary particles are commonly called “flavors”, and the neutrinos here are considered to have distinctly different flavor (Table 6) (Alt ” yn screen 2).
Now that we have experimental evidence for six leptons, a relevant question is “Are there more?” .
The present standard model assumes that there are no more than three generations. One of the pieces of experimental evidence for that is the measured hydrogen / helium abundance ratio in the universe. When the process of nucleosynthesis from the big bang is modeled, the number of types of neutrinos affects the abundance of helium. The observed abundance agrees with three types of neutrinos (Nave screen 3).
Flavor Mass
(GeV/c 2) Electric Charge
(e)
electron neutrino.