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Particle physics
Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them
Atoms include atomic constituents such as electron,proton, and nuetrons , particles produced by radiative and scattering processes, such as photons ,neutrinos and muons, as well as a wide range of exotic particles.
Words to Know
Antiparticles: Subatomic particles similar to the proton, neutron, electron, and other subatomic particles, but having one property (such as electric charge) opposite them.
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Standard Model
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The Standard Model of particle physics contains 12 flavors of elementary fermions , plus their corresponding antiparticles, as well as elementary bosons that mediate the forces and the still undiscovered Higgs boson.
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The Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, since it is fundamentally incompatible with Einstein’s general relativity.
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There are likely to be hypothetical elementary particles not described by the Standard Model, such as the graviton , the particle that would carry the gravitational force or the sparticles , supersymmetric partners of the ordinary particles.
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In the standard model , the quarks , leptons , and gauge bosons are elementary particles
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Historically, the hardons (mesons and baryons such as the proton and neutron) and even whole atoms were once regarded as elementary particles.
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Five important subatomic particles
Proton. The proton is a positively charged subatomic particle with an atomic mass of about 1 amu. Protons are one of the fundamental constituents of all atoms. Along with neutrons, they are found in a very concentrated region of space within atoms referred to as the nucleus.
Neutron. A neutron has a mass of about 1 amu and no electric charge. It is found in the nuclei of atoms along with protons. The neutron is normally a stable particle in that it can remain unchanged within the nucleus for an infinite period of time.
Leptons
1st Generation
2nd Generation
3rd Generation
Name
symbol
Name
symbol
Name
symbol
Electron
e?
Muon
??
Tauon
??
Electon neutrino
?e
Muon neutrino
??
Tauon neutrino
??
Quarks
Up quark
u
Charm quark
c
Top quark
t
Down quark
d
Strange qzzuark
s
Bottom quark
b
What are Quarks?
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 . 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...).
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Because quarks join with eachother to form particles with integer charge, not every kind of combination of quarks is possible. There are two basic types of hadrons. They are baryons, which are composed of three quarks, and mesons which are made up of a quark and an antiquark. Two examples of a baryon are the neutron and the proton
Properties
Name
Symbol
Charge
up
u
+2/3
down
d
-1/3
charm
c
+2/3
strange
s
-1/3
Top
t
+2/3
Bottom
b
-1/3
Quarks possess a property to which has been given the name color. Just as electric charge originates electromagnetic interactions, color originates strong interactions. Thus color can also be called ``strong charge´´. Quarks come in three different states of color, conventionally called red, green and blue. A proton or a neutron is made of three quarks of different colors. Since equal amounts of red, green and blue result in white, neutrons and protons can be said to be white. In fact, according to the theory of strong interactions, only white objects can exist in isolation. Colored particles - such as quarks - can only exist as components of white objects. This property is called confinement. The region of space to which quarks are confined to form a proton or a neutron - represented by the crystal ball in the picture - is usually called a bag.
Flavor
Protons and neutrons are made of three quarks. Quarks, like protons and neutrons, have spin s=1/2. These three spins must add up to form the spin of the proton or neutron. According to quantum mechanics, in order to obtain a proton or neutron with spin up, we must combine two quarks with spin up with one quark with spin down. Symmetrically, in order to obtain a proton or neutron with spin down, we must combine two quarks with spin down with one quark with spin up. These rules are illustrated in the pictures.
The Neutron in the Quark Model
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. 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.
Beyond the Standard Model
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Grand unification One extension of the Standard Model attempts to combine the elecroweak interaction with the strong interaction into a single 'grand unified theory' (GUT). Such a force would be spontaneously broken into the three forces by a Higgs like mechanicsm. The most dramatic prediction of grand unification is the existence of X & Y bosons, which cause proton decay.
Supersymmetry
Experiment
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Brookhaven National Laboratory, located on Long Island, USA. Its main facility is the Relativistic Heavy Ion Collider which collides heavy ions such as gold ions and polarized protons. It is the world's first heavy ion collider, and the world's only polarized proton collider.
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Budker Instituite of Nuclear Physics (Novosibrick,Russia)
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CERN, located on the French-Swiss border near Geneva . Its main project is now the Large Hardon Collider (LHC), which had its first beam circulation on 10 September 2008 and is the world's most energetic collider. Earlier facilities include LEP, the Large Electron Positron collider, which was stopped in 2001 and then dismantled to give way for LHC; and SPS, or the Super Proton Synchrotron, which is being reused as a pre-accelerator for LHC.
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DESY, located in Hamburg, Germany. Its main facility is HERA, which collides electrons or positrons and protons..
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KEK, the High Energy Accelerator Research Organization of Japan, located in Tsukuba, Japan. It is the home of a number of experiments such as K2K, a neutrino oscillation experiment and Belle, an experiment measuring the CP-symmetry violation in the B-meson.
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SLAC, located near Palo Alto, USA. Its main facility is PEP-II, which collides electrons & positrons and .
The future
Particle physicists internationally agree on the most important goals of particle physics research in the near and intermediate future.
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overarching goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the standard model.. There are several powerful experimental reasons to expect new physics, including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at accessible energy scales. Most importantly, though, there may be unexpected and unpredicted surprises which will give us the most opportunity to learn about nature.
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Much of the efforts to find this new physics are focused on new collider experiments. A (relatively) near term goal is the completion of the Large Hadron Collider (LHC) in 2008 which will continue the search for the Higgs boson , supersymmetric particles, and other new physics. An intermediate goal is the construction of the International Linear Collider (ILC) which will complement the LHC by allowing more precise measurements of the properties of newly found particles. A decision for the technology of the ILC has been taken in August 2004, but the site has still to be agreed upon.
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Additionally, there are important non-collider experiments which also attempt to find and understand physics beyond the standard model. One important non-collider effort is the determination of the nuetrino masses since these masses may arise from neutrinos mixing with very heavy particles. In addition, cosmological observations provide many useful constraints on the dark matter, although it may be impossible to determine the exact nature of the dark matter without the colliders. Finally, lower bounds on the very long lifetime of the proton put constraints on Grand Unification Theories at energy scales much higher than collider experiments will be able to probe any time soon.
Reference
The Review of Particle Physics
C. Amsler et al
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Supersymmetry extends the Standard Model by adding an additional class of symmetries to the Lagrangian. These symmetries exchange fermionic particles with bosonic ones. Each particle in the Standard Model would have a superpartner whose spin differs by 1/2 from the ordinary particle. Due to the breaking of supersymmetry , the sparticles are much heavier than their ordinary counterparts; they are so heavy that existing particle colliders would not be powerful enough to produce them. However, some physicists believe that sparticles will be detected when the Large Hadron Collider at CERN begins running .
Preon theory
String theory
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String theory String Theory is a theory of physics where all "particles" that make up matter are comprised of strings that exist in an 11-dimensional universe These strings vibrate at different frequencies which determine mass, electric charge, color charge, and spin String theory posits that our universe is merely a 4-brane, inside which exist the 3 space dimensions and the 1 time dimension that we observe. The remaining 6 theoretical dimensions are either very tiny and curled up (and too small to affect our universe in any way) or simply do not/cannot exist in our universe (because they exist in a grander scheme called the "multiverse" outside our known universe).
According to preon theory there are one or more orders of particles more fundamental than those (or most of those) found in the Standard model. The most fundamental of these are normally called preons, which is derived from "pre-quarks". In essence, preon theory tries to do for the Standard model what the Standard Model did for the particle zoo that came before it. Most models assume that almost everything in the Standard Model can be explained in terms of three to half a dozen more fundamental particles and the rules that govern their interactions. Interest in preons has waned since the simplest models were experimentally ruled out in the 1980s.
As far as is presently known, there exist six different types of quarks. These types are known as flavors and have been given the following names: up, down, strange, charm, top and bottom. One property which differs from one flavor to the other is mass. The up and down quarks have the smallest masses. These are the only flavors which constitute ordinary stable matter. The other flavors are present only in unstable particles produced in collisions. In the present book, the up quark is represented as an upper hemisphere and the down quark is represented as a lower hemisphere. This is a mere visualization convention; in fact, quarks are ``point-like´´ in the standard theory of elementary particles. The proton is made up of two up quarks and one down quark, while the neutron is made up of two down quarks and one up quark. The up quark has positive electric charge equal in absolute value to 2/3 that of the electron. The down quark has negative electric charge equal in absolute value to 1/3 that of the eletron. Check that these charges add up correctly to give, for the neutron, zero total charge and, for the proton, positive charge equal in absolute value to that of the electron.
Spins
Color
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Electron. Electrons are particles carrying a single unit of negative electricity with a mass of about 1/1800 amu, or 0.0055 amu. All atoms contain one or more electrons located in the space outside the atomic nucleus. Electrons are arranged in specific regions of the atom known as energy levels. Each energy level in an atom may contain some maximum number of electrons, ranging from a minimum of two to a maximum of eight.
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Neutrino. Neutrinos are elusive subatomic particles that are created by some of the most basic physical processes of the universe, like decay of radioactive elements and fusion reactions that power the Sun
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Standard Model
The Standard Model of particle physics contains 12 flavors of elementary fermions , plus their corresponding antiparticles, as
well as elementary bosons that mediate the forces and the still undiscovered Higgs boson.
•
The Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, since it is
fundamentally incompatible with Einstein’s general relativity.
•
There are likely to be hypothetical elementary particles not described by the Standard Model, such as the graviton , the particle
that would carry the gravitational force or the sparticles , supersymmetric partners of the ordinary particles.
•
In the standard model , the quarks , leptons , and gauge bosons are elementary particles
•
Particle Generations
Historically, the hardons (mesons and baryons such as the proton and neutron) and even whole atoms were once regarded as
elementary particles
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Positron. A positron is a subatomic particle identical in every way to an electron except for its electric charge. It carries a single unit of positive electricity rather than a single unit of negative electricity.
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Atomic mass unit (amu): A unit of mass measurement for small particles.
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Atomic number: The number of protons in the nucleus of an atom.
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Elementary particle: A subatomic particle that cannot be broken down into any simpler particle.
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Energy levels: The regions in an atom in which electrons are most likely to be found.
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Gluon: The elementary particle thought to be responsible for carrying the strong force (which binds together neutrons and protons in the atomic nucleus).
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Graviton: The elementary particle thought to be responsible for carrying the gravitational force.
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Isotopes: Forms of an element in which atoms have the same number of protons but different numbers of neutrons.
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Lepton: A type of elementary particle.
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Photon: An elementary particle that carries electromagnetic force.
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Quark: A type of elementary particle.
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Spin: A fundamental property of all subatomic particles corresponding to their rotation on their axes.
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According to this methodology: particles normally
associated with matter are fermions , having half integer spin; they are divided into twelve flavours
Particles associated with fundemental forces are bosons, having integer spin
Historically, the hardons (meson and baryons such as the proton and neutron ) and even whole atoms were once regarded as
elementary particles
By 20th century by the idea of “quanta”", which revolutionised the understanding of electromagnetic radiation and brought
about quantum mechanics.
All elementary particles are either bosons or fermions (depending on their spin). The spin- statistics theorem identifies the
resulting quantum statistics that differentiates fermions from bosons.
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