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Jacob Foster
Jacob Foster

Introduction To Elementary Particles (2nd Edition)

David Griffiths is Professor of Physics at the Reed College in Portland, Oregon. After obtaining his PhD in elementary particle theory at Harvard, he taught at several colleges and universities before joining the faculty at Reed in 1978. He specializes in classical electrodynamics and quantum mechanics as well as elementary particles, and has written textbooks on all three subjects. Permissions Request permission to reuse content from this site

Introduction to Elementary Particles (2nd edition)


In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles.[1] Particles currently thought to be elementary include electrons, the fundamental fermions (quarks, leptons, antiquarks, and antileptons, which generally are matter particles and antimatter particles), as well as the fundamental bosons (gauge bosons and the Higgs boson), which generally are force particles that mediate interactions among fermions.[1] A particle containing two or more elementary particles is a composite particle.

In the Standard Model, elementary particles are represented for predictive utility as point particles. Though extremely successful, the Standard Model is limited by its omission of gravitation and has some parameters arbitrarily added but unexplained.[10]

According to the current models of big bang nucleosynthesis, the primordial composition of visible matter of the universe should be about 75% hydrogen and 25% helium-4 (in mass). Neutrons are made up of one up and two down quarks, while protons are made of two up and one down quark. Since the other common elementary particles (such as electrons, neutrinos, or weak bosons) are so light or so rare when compared to atomic nuclei, we can neglect their mass contribution to the observable universe's total mass. Therefore, one can conclude that most of the visible mass of the universe consists of protons and neutrons, which, like all baryons, in turn consist of up quarks and down quarks.

In terms of number of particles, some estimates imply that nearly all the matter, excluding dark matter, occurs in neutrinos, which constitute the majority of the roughly 1086 elementary particles of matter that exist in the visible universe.[13] Other estimates imply that roughly 1097 elementary particles exist in the visible universe (not including dark matter), mostly photons and other massless force carriers.[13]

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 Higgs boson, which was reported on July 4, 2012, as having been likely detected by the two main experiments at the Large Hadron Collider (ATLAS and CMS).[1] The Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, however, since it is not known if it is compatible with Einstein's general relativity. There may be hypothetical elementary particles not described by the Standard Model, such as the graviton, the particle that would carry the gravitational force, and sparticles, supersymmetric partners of the ordinary particles.[14]

In the Standard Model, vector (spin-1) bosons (gluons, photons, and the W and Z bosons) mediate forces, whereas the Higgs boson (spin-0) is responsible for the intrinsic mass of particles. Bosons differ from fermions in the fact that multiple bosons can occupy the same quantum state (Pauli exclusion principle). Also, bosons can be either elementary, like photons, or a combination, like mesons. The spin of bosons are integers instead of half integers.

.................. An experimentalist's view of a proton. How many things .................. can you find wrong in this gif? For a theorist's view of the .................. proton, see Derek Leinweber's web page. Updates and Weekly Deadlines Posted Here:Problem Set 8, due Wednesday April 5 at 12:20 PM, is here.The texts for the course are:David Griffiths, "Introduction to elementary particles," 2nd editionW.N. Cottingham, D.A. Greenwood, "An introduction to nuclear physics," 2nd editionBe sure to have ordered your PDG booklet from the PDG.for the first exam.The Nuclide Map that I like using (from Brookhaven National Lab) is here.Other useful ones are here.

Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. They are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge.

Elementary fermions are grouped into three generations, each comprising two leptons and two quarks. The first generation includes up and down quarks, the second strange and charm quarks, and the third bottom and top quarks. All searches for a fourth generation of quarks and other elementary fermions have failed,[18][19] and there is strong indirect evidence that no more than three generations exist.[nb 2][20][21][22] Particles in higher generations generally have greater mass and less stability, causing them to decay into lower-generation particles by means of weak interactions. Only first-generation (up and down) quarks occur commonly in nature. Heavier quarks can only be created in high-energy collisions (such as in those involving cosmic rays), and decay quickly; however, they are thought to have been present during the first fractions of a second after the Big Bang, when the universe was in an extremely hot and dense phase (the quark epoch). Studies of heavier quarks are conducted in artificially created conditions, such as in particle accelerators.[23]

Having electric charge, mass, color charge, and flavor, quarks are the only known elementary particles that engage in all four fundamental interactions of contemporary physics: electromagnetism, gravitation, strong interaction, and weak interaction.[12] Gravitation is too weak to be relevant to individual particle interactions except at extremes of energy (Planck energy) and distance scales (Planck distance). However, since no successful quantum theory of gravity exists, gravitation is not described by the Standard Model.

At the time of the quark theory's inception, the "particle zoo" included a multitude of hadrons, among other particles. Gell-Mann and Zweig posited that they were not elementary particles, but were instead composed of combinations of quarks and antiquarks. Their model involved three flavors of quarks, up, down, and strange, to which they ascribed properties such as spin and electric charge.[24][25][26] The initial reaction of the physics community to the proposal was mixed. There was particular contention about whether the quark was a physical entity or a mere abstraction used to explain concepts that were not fully understood at the time.[30]

Spin is an intrinsic property of elementary particles, and its direction is an important degree of freedom. It is sometimes visualized as the rotation of an object around its own axis (hence the name "spin"), though this notion is somewhat misguided at subatomic scales because elementary particles are believed to be point-like.[69]

David Griffiths is Professor of Physics at the Reed College in Portland, Oregon. After obtaining his PhD in elementary particle theory at Harvard, he taught at several colleges and universities before joining the faculty at Reed in 1978. He specializes in classical electrodynamics and quantum mechanics as well as elementary particles, and has written textbooks on all three subjects.

Properties of a quantum field that represents an elementary particle and a quantum field that mediates an interaction between particles are analyzed. This analysis relies on fundamental physical principles. The mathematical structure of these fields proves that they are completely different physical objects. A further analysis proves that a quantum field that represents an elementary massive particle and a quantum field that represents a massless particle have a completely different mathematical structure. The results are used in an examination of free spin-1/2 elementary massive particles and other free elementary particles that have an integral spin. Inherent inconsistencies are found for elementary massive particles that have an integral spin and for the Majorana neutrino. The analysis also proves that interaction mediating fields do not represent a genuine particle.

Recommended Corequisite or Preparatory: PHYS 451. Production, interactions and structure of subatomic particles, including radioactivity, accelerators, detectors, classification of elementary particles, quark model, nuclear properties, nuclear models and nuclear reactions. Available for graduate credit.

The aim with the course is to give the students an elementary and solid introduction to the standard model of elementary particles and forces. Besides the phenomenological treatment of elementary particles quantum field theory will be introduced. The approach will be extended with an outlook to discuss many-body physics in condensed matter. After a successful course the student can

One of the most striking phenomena that can be observed in high-energy collisions of elementary particles is the production of highly collimated bunches of particles. These objects are known as hadronic jets. The word 'hadronic' refers to the fact that jets are made up of hadrons, particles which can interact through the strong force, the force that keeps atomic nuclei bound together. If we look inside a jet we find protons and neutrons, the constituents of nuclei, and other less well known hadrons such as pions, which are commonly observed as cosmic rays, as well as kaons, rho mesons, etc.

The book is organised as follows. In chapter 2 we discuss jet algorithms, which are the procedures that are used to rigorously define jets and to extract them from the multitude of hadrons present in a typical final state at high-energy colliders. Chapter 3 will be devoted to QCD, the theory of strong interactions governing the dynamics of quarks and gluons. In particular, we will describe the theoretical tools within QCD that can be used to describe the properties of jets. Finally, in chapter 4 we will discuss how, from a set of observed jets, it is possible to extract information on the elementary event that has produced them. Such techniques are extremely important in the search for new particles, especially when they are expected to decay into quarks and gluons, giving rise to jets as final states. This is the starting point of a new subject, sometimes referred to as 'jetography' [17], where jets are the basic ingredients used to describe elementary final states, much as geographic maps are used to describe the Earth. 041b061a72


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