Antiquark

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  Introductory Matter Physics & its Applications

  • (Author)
  • 2014(Publication Date)
  • College Publishing House

    (Publisher)

  This model contains six flavors of quarks (q), named up (u), down (d), charm (c), strange (s), top (t), and bottom (b). Antiparticles of quarks are called Antiquarks , and are denoted by a bar over the symbol for the corresponding quark, such as u for an up Antiquark. As with antimatter in general, Antiquarks have the same mass, ______________________________ WORLD TECHNOLOGIES ______________________________ mean lifetime, and spin as their respective quarks, but the electric charge and other charges have the opposite sign. Quarks are spin-1 ⁄ 2 particles, implying that they are fermions according to the spin-statistics theorem. They are subject to the Pauli exclusion principle, which states that no two identical fermions can simultaneously occupy the same quantum state. This is in contrast to bosons (particles with integer spin), of which any number can be in the same state. Unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction. The resulting attraction between different quarks causes the formation of composite particles known as hadrons . The quarks which determine the quantum numbers of hadrons are called valence quarks ; apart from these, any hadron may contain an indefinite number of virtual (or sea ) quarks, Antiquarks, and gluons which do not influence its quantum numbers. There are two families of hadrons: baryons, with three valence quarks, and mesons, with a valence quark and an Antiquark. The most common baryons are the proton and the neutron, the building blocks of the atomic nucleus. A great number of hadrons are known, most of them differentiated by their quark content and the properties these constituent quarks confer. The existence of exotic hadrons with more valence quarks, such as tetraquarks (qqqq) and pentaquarks (qqqqq), has been conjectured but not proven. Elementary fermions are grouped into three generations, each comprising two leptons and two quarks.

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  The Mystery of the Missing Antimatter

  • Helen R. Quinn, Yossi Nir(Authors)
  • 2010(Publication Date)
  • Princeton University Press

    (Publisher)

  Before we proceed, it may be worth reviewing the language of matter and antimatter in terms of quarks. Quarks are matter, Antiquarks are antimatter. Quarks and Antiquarks, like electrons and positrons, are thought to be fundamental spin-1/2 particles; we have no evidence that suggests they have any substructure, or indeed even any measurable size. The fermionic (spin-1/2 or spin-3/2) hadrons, known as baryons, have a basic substructure of three quarks. For example, the proton is made of two up quarks and one down quark, while the neutron is made of two down quarks and one up quark. Antibaryons are the corresponding antimatter particles made from three Antiquarks. (Note that the difference between a neutron (made of two down quarks with charge −1/3 each and one up 98 c h a p t e r 1 0 quark with charge +2/3) and an antineutron (made of two down Antiquarks with charge +1/3 and one up Antiquark with charge −2/3) is no longer a puzzle.) Mesons are particles that are neither matter nor antimatter but an equal mixture of both—their basic structure is one quark plus one Antiquark. So having classified two types of substance we come upon the third option, a substance that mixes matter and antimatter. But if matter and antimatter can be produced together then nothing forbids their also disappearing together; though of course something else must arise since the laws of conservation of energy, momentum, electric charge, and so on, continue to be true. All mesons are unstable and eventually decay, usually producing lighter mesons. Decays of the lightest mesons produce leptons plus antilep- tons, or two or more photons. (Another piece of the jargon—spin-1/2 particles which are not subject to the strong nuclear force, such as electrons, muons, and neutrinos, are called leptons.) From the quark point of view, the baryon number, which counts baryons minus antibaryons, is exactly three times the quark number (number of quarks minus Antiquarks).

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  Inquiry into Physics

  • Vern Ostdiek, Donald Bord(Authors)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  The three quark colors were labeled after the three primary colors of the artist’s palette: red, blue, and green. Antiquarks are colored antired, antiblue, and antigreen (Figure 12.21). The fact that color is not an observed property of hadrons indicates that these particles are “colorless.” If they are composed of colored quarks, then the way the colors come together within the hadron must be such as to produce something with no net color, something that is color neutral. For this to be true, the three quarks that make up baryons must each possess a color different from their companions, one red, one blue, and one green. The addition of the primary colors produces the result we call “white,” so baryons containing three different colored quarks are considered to be white or neutral as concerns the color charge. In an analogous manner, for mesons to be color-neutral requires them to be made up of a quark of one color and an Antiquark possessing the corresponding anticolor. Returning to our previous example of the H9266 1 meson, we see in the light of this new color physics that if the u quark is red, the d quark must be antired. You have probably noticed that the language of particle physics is rather whimsical in comparison with the other areas of physics that we have studied. To carry this whimsy one step further, we note that often the different types of quarks, u, d, s (and others that we will shortly introduce), are designated quark flavors. Quarks come in six flavors (not counting the antiflavors), and each flavor comes in three colors. Color is another example of an internal quantum number, like unitary spin. It is not directly observed in hadrons, and it cannot be used to classify them. Moreover, it does not influence the interactions among hadrons.

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  Understand Physics: Teach Yourself

  • Jim Breithaupt(Author)
  • 2010(Publication Date)
  • Teach Yourself

    (Publisher)

  Quarks combine in threes to form particles like the proton and the neutron. Antiquarks also combine in threes to form antiparticles like the antiproton and the antineutron. Such composite particles are collectively referred to as

  baryons .

  4   A meson consists of a quark and an Antiquark.

  In terms of the charge of the electron, the u, c and t quarks each carry a charge of + e and the other three quarks carry a charge of − e . An Antiquark carries an equal and opposite charge to its corresponding quark. The symbol for an Antiquark is the same as for a quark but with a bar over the top. For example, (pronounced ‘dee bar’) represents the symbol for a down Antiquark. So:

   

  • A proton is composed of two up quarks and a down quark.
  • A neutron consists of an up quark and two down quarks.
  • A pion consists of an up or down quark and an up or down Antiquark.
  • Strange particles contain strange quarks or Antiquarks.

  The creation of pions and strange particles and antiparticles can be explained using the quark model. For example, if a proton at high speed collides with another proton, the following interaction could take place:

  proton +proton → positive pion +proton +neutron

  In quark terms: In the collision, a down quark and a down Antiquark are created from the kinetic energy of the high-speed proton. The quarks and the Antiquark regroup to form a positive pion, a proton and a neutron.

  The quark model was confirmed by physicists using the Stanford Linear Accelerator to accelerate electrons to speeds within a tiny fraction of the speed of light and use them to bombard a target. These electrons were scattered by the target nuclei in directions corresponding to three hard centres in every neutron and proton.

  Where do electrons fit into this model? The answer is that they do not. Electrons, positrons and certain other particles and antiparticles are thought to be elementary in the sense that they are not composed of smaller particles. These particles and antiparticles are collectively referred to as leptons

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  Andrei Sakharov: Quarks And The Structure Of Matter

  Quarks and the Structure of Matter

  • Harry J Lipkin(Author)
  • 2013(Publication Date)
  • WSPC

    (Publisher)

  We now believe that the forces binding quarks into a proton are so strong that enormous energy would be needed to knock a quark out of a proton. These building blocks are combined in groups of two or three by such strong forces that it is impossible to separate out single quarks. Physicists have tried to break these groups of building blocks into quarks by accelerating them to produce very high speed collisions. But they are defeated here by Einstein’s principle relating energy and matter. At very high speeds they have so much energy that the energy is turned into making more building blocks.

  We can never create a single quark just as we can never create a single electron. An electron has a negative electric charge and can only be created together with another particle like a positron that has a positive electric charge. Similarly a quark has a definite color charge and can only be created with an Antiquark which has an opposite color charge. But the electric force between electron and a positron decreases with distance just like the gravitational force between a rocket and the Earth. If a rocket is hit hard enough it can escape from the Earth. In the same way the electron can get away from the positron and be observed as a single electron.

  But the very strong forces between a quark and an Antiquark can never allow a single quark to escape. When a collision between two protons has enough energy to knock a quark out of the proton, the energy is converted into new quarks. A quark-Antiquark pair can be created in the space between the struck quark and the two other quarks from the proton. The Antiquark is then captured by the struck quark to make a meson and the new quark joins the two old quarks to make a new proton. The isolated quark is not observed, only a cloud of new particles.

  The Structure of Matter

  What is the structure of matter, and why are such accelerators necessary to study it, rather than ordinary microscopes? To get some feeling for the answer to these questions, let us first consider how scientists (or laymen, for that matter) study the structure of more familiar objects. When we look at a brick wall from a distance, it is hard to discern that it is made up of individual bricks and cement. From far it looks as if it were made of one homogeneous material. Only by coming closer to it, or looking at it through binoculars or a small telescope, can we see its fine details and establish that it is constructed of building blocks arranged in a very special and regular pattern to provide the stability and strength that a wall needs, and that there is cement between the bricks that makes them stick together. If we look at the bricks even closer, we see that each individual brick has a structure and is made of even smaller constituents. In the same way, a bar of iron that appears to be a homogeneous structure is really made up of atoms arranged in a specific pattern to give iron its special hardness and smoothness.

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  Understanding The Universe: From Quarks To The Cosmos

  From Quarks to the Cosmos

  • Donald Lincoln(Author)
  • 2004(Publication Date)
  • World Scientific

    (Publisher)

  The name of the strange quark was chosen because it was thought that this quark carried the “strange” property that caused some particles to exist for a longer time than one would ordinarily expect. So the names, while somewhat obscure, have a historical basis. Quarks were predicted to have some unusual properties. The proton and electron have equal and opposite electrical charge and further, they were understood to have a fundamental (that is, the smallest possible) electrical charge. The charge on a proton is 1 unit, while the electron carries 1 unit of electrical charge. However, quarks, as originally imagined, were thought to have an even smaller charge, a somewhat heretical postulate. Up quarks were to have a positive electrical charge, but only two-thirds that of the proton q u a r k s a n d l e p t o n s 109 ( 2 / 3 charge). Similarly, the down and strange quarks were thought to have a negative electrical charge, but one-third that of an electron ( 1 / 3 charge). Antimatter quarks have opposite electrical charge as compared to their matter counterparts (anti-up has a 2 / 3 charge, while anti-down (and anti-strange) have 1 / 3 electrical charge). Another property of quarks is their quantum mechanical spin. As discussed in Chapter 2, particles can be broken down into two differ-ent spin classes: bosons, with integer spin (…, 2, 1, 0, 1, 2, …) and fermions with half-integer spin (…, 5 / 2, 3 / 2, 1 / 2, 1 / 2, 3 / 2, 5 / 2, …) (where “…” means “The pattern continues”). Quarks are fermions with spin 1 / 2. While quarks have some other properties that we will discuss later, we now turn to how quarks combine to make up many of the parti-cles described in Chapter 2. To begin with, let’s discuss mesons, the medium mass particles. Gell-Mann and Zweig decided that mesons consisted of two objects: a quark and an antimatter quark (called an Antiquark). For instance, the meson (pronounced “pi plus”) consists of an up quark and an anti-down quark, which we write as ud – .

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  Facts and Mysteries in Elementary Particle Physics

  • Martinus J G Veltman(Author)
  • 2003(Publication Date)
  • WSPC

    (Publisher)

  up quark .

  The color charge of the quarks (see Chapter 2 ) plays no role in this discussion; the bound states are color neutral. This means that if there is for example a red quark, there is also an anti (red quark). The bound state will be a mixture of the possible color combinations red–antired, green–antigreen and blue–antiblue.

  The pions (π ) and kaons (K ) have been mentioned before, in Chapter 6 . These particles were copiously produced at the first big machines (CERN, BNL), and became the subject of intense experimentation. All particles shown on the second line were discovered before it was realized that they were bound states of a quark and an Antiquark, and the names shown are those given in the pre-quark era. The electric charges of these particles are as shown, if not indicated (η and η ′) they are zero.

  The table is strictly speaking not correct, because the π 0 , η and η ′ are not precisely the bound states listed above them, but certain mixtures. For example, the π 0 is a mixture of

  dd

  and . There is no need to worry about that here.

  In 1961 all these particles were classified in a particular manner, best shown in a figure. This most remarkable figure, introduced by Gell-Mann in his paper entitled “The eightfold way”, immediately took hold in particle physics. As we will see it is suggestive of a construction built up from triangles, and that is indeed what led to the introduction of quarks in 1964. The nine particles are grouped into an octet (8 particles) and a singlet.

  In this figure the particles are arranged by strangeness and charge; for our purposes the strangeness of a particle is determined by the number of strange quarks in that particle. For every strange quark count − 1, and + 1 for its antiparticle, the strange quark . For example, K − has one s quark, and thus has strangeness − 1. The strangeness is the same for particles on the same horizontal line; charge is the same for particles on the same vertical line. The classification into octet and singlet is related to the behaviour of the bound states under exchange of the quarks. The η ′ is supposedly an equal mixturee of ,

  dd

  and . It remains the same thing if the quarks are interchanged, for example, if the d and d are interchanged with s and . Particles in the octet interchange with each other, for example that same quark interchange (d ↔ s and d ↔ ) exchanges K 0 and K 0

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  The Poetry of Physics and the Physics of Poetry

  • Robert K Logan(Author)
  • 2010(Publication Date)
  • WSPC

    (Publisher)

  Although one can explain the SU(3) symmetry of hadrons in terms of quarks, a quark has never been seen in isolation because of the phenomenon of confinement, which is not totally understood. It is just an empirical fact that quarks never can be separated from the hadrons in which they exist. The closest physicists have come to seeing a quark is when they are produced in high energy collisions and one see three jets of many hadrons clustered together. The force between quarks that gives rise to their confinement is due to the exchange of gluons. Gluons play the same role in the quark-quark force that the photon plays in the force between charged particles and mesons play in the force between nucleons. Like photons gluons have spin 1 but they come in eight different colour charges. The colour in colour charge is not the actual colours of visible light but they are a metaphorical way of describing the different states of gluons. Quarks also have three different colour charges and Antiquarks have three kinds of anticolours.

  The interactions of quarks and gluons are described by Quantum Chromodynamics (QCD), which is a theory of the fundamental force of nature, the strong interaction of baryons and mesons, i.e. hadrons, and is patterned on Quantum Electrodynamics. It is an essential part of the Standard Model of particle physics and describes and explains a huge body of experimental data collected over many years.

  The Weak Interaction

  The weak interaction is one of the four basic forces of nature along with the strong interaction, gravity and electromagnetism. It is the force that accounts for the decay of the strongly interacting hadrons and is extremely weak with a strength of 10−11 that of the electromagnetic force and 10−13 of the strong interaction. The first example of the weak interaction that was encountered was the beta decay of a free neutron into a proton, an electron and an antineutrino, n → p + e + . [A note on notation: the neutrino will be represented by νe and the antineutrino by ] The neutrino and antineutrino are uncharged elementary particles with a minuscule, but nonzero mass that travels very close to the speed of light and is difficult to observe because they pass through ordinary matter for the most part without interacting. The existence of this particle was first suggested by Wolfgang Pauli to explain the lack of conservation of energy, momentum and angular momentum when neutron decay into a proton and an electron was first observed. Neutrino was first detected in 1956 when they were observed in induced beta decay ( + p → n + e+

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  General Chemistry

  • Linus Pauling(Author)
  • 2014(Publication Date)
  • Dover Publications

    (Publisher)

       Much of the knowledge about the fundamental particles has been obtained during the last decade. The scientists who have been working in this field have made many completely unexpected discoveries, which are changing our ways of thinking about the world. Just as the discoveries in the field of atomic and molecular science, discussed in earlier chapters, and the field of nuclear science, to be discussed in the following chapter, have had profound effects upon our daily lives, changing the nature of our civilization and especially the methods of waging war, so may we expect that the new knowledge about fundamental particles will in the course of time have equally profound effects upon our lives.

  25-1. The Classification of the Fundamental Particles

  At the present time it is convenient to classify the thirty-four fundamental particles in the following way:

               8 baryons (the proton, the neutron, and six heavier particles)

               8 antibaryons

               8 mesons and antimesons

               8 leptons and antileptons

               The photon

               The graviton

       Most of the fundamental particles can be described as constituting either matter or antimatter. The existence of these two kinds of matter was predicted in 1928, on the basis of relativistic quantum mechanics, by P. A. M. Dirac (born 1902), the English theoretical physicist who first developed a theory of quantum mechanics compatible with the theory of relativity. His prediction has been thoroughly confirmed by experiment. Every electrically charged particle has a counterpart that is identical with it in some properties and opposite to it in others: the masses and spins are identical, but the electric charges are opposite. For example, the electron, which constitutes a part of ordinary matter, and the positron, which is the antielectron, have opposite electric charges, –e and +e , respectively; their masses are the same; and each has a spin represented by the spin quantum number ½, which permits two ways of orienting the spinning particle in a magnetic field. Some neutral particles have antiparticles and some are their own antiparticles. Whenever a particle and the corresponding antiparticle come together they annihilate each other. Their masses are totally converted into high-energy light waves or, in some cases, into lighter particles moving with great speeds. The Einstein equation E = mc 2

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  The Weak Interaction in Nuclear, Particle and Astrophysics

  • K. Grotz(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  preons (see e.g. Schrempp and Schrempp (1985) and Mohapatra (1986a)). The members of the various families would then behave as different excited states of bound preon systems. This idea would also require a new, very strong interaction, holding together the preons inside the elementary particles. In such models, the weak interaction could be viewed as a residual interaction of this new force, in much the same way as we now view the nuclear force as a residual interaction of the so-called colour interaction between quarks.

  Table 1.2: History of the discovery of the families of quarks and leptons (Cline (1987)).

  Particle	Discovery	Generation or family
  Electron	≈ 1900	1
  Neutron (d quark)	≈ 1932	1
  Electron neutrino	≈ 1957	1
  Muon	≈ 1938–48	2
  Strange particle (s quark)	≈ 1948–50	2
  Charm (c quark)	1974	2
  Muon neutrino (νμ )	≈ 1962	2
  τ lepton	1975	3
  b quark	≈ 1977	3
  t quark	?	3
  ντ	1975–1978 (only indirectly)	3
  L lepton	ML > 41 GeV 90% Confidence	4
  b′ quark	Mb ′ > 23 GeV	4
  t′ quark	Mt ′ > 23 GeV	4
  νL	?	4

  1.1.2  Antipartides

  For every particle, i.e. for each of the elementary fermions referred to above, there exists an antiparticle. This has the same mass, spin, isospin and eigenparity as the particle, and if the particle is unstable, the antiparticle has the same lifetime. It differs from the particle in the sign of its electric charge, and in the signs of all its other additive quantum numbers (see Section 1.3 ). That antipartides with these properties must exist is a fundamental result of relativistic quantum field theory. The notation for antiparticles is not uniform. The antiparticle of any fermion f may be unambiguously denoted by fC . The ‘C’ stands for ‘charge conjugation’, this terminology reflects the change in the sign of the charge on transition to the antiparticle. However, this notation is not used very often. The charge conjugation operation effects the transition to an antiparticle state; however care is needed if the state of motion of the particle has a role to play, as with the neutrino (see Subsections 1.3.8 –1.3.10

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  Developments in Modern physics

  • Nelson Boli´var(Author)
  • 2023(Publication Date)
  • Arcler Press

    (Publisher)

  The antiproton is the proton’s antiparticle. It possesses all of the properties of a proton except for the fact that this is negatively charged. The π 0 mesons and the photon are examples of totally neutral particles that have their antiparticles. Antiparticles are represented by a bar over the particle sign. As a result, p, and n are antiprotons and antineutrons, respectively. Antimatter is made up of antineutrons, antiprotons, and antielectrons (positrons) while matter is made up of neutrons, protons, and electrons. Figure 4.2 depicts antimatter and matter atoms. Antimatter is kept together by similar electric Developments in Modern Physics 92 forces which keep matter together (Chiu, 1966; Toussaint and Wilczek, 1983). Figure 4.2. Antimatter and matter. Source: https://www.indiatoday.in/education-today/gk-current-affairs/story/ where-is-all-the-antimatter-scientists-create-antihydrogen-atom-to-find-an- swers-html-1206368-2018-04-06. (Remember that in antimatter, the +ve and –ve signs are reversed). High-energy accelerators have previously produced the antihelium nucleus. When antiparticles and particles collide, they destroy one another, leaving just energy. When an electron collides with a positron, for instance, they annihilate as per the reaction (Smarandache, 2009; Adamczyk et al., 2013). e – + e + → 2γ (2) Photons of electromagnetic energy have been represented by 2γ’s. (For energy and momentum conservation, two gamma rays are required). Other particles may be created with this energy. Particles, on either hand, may be formed by transforming the energy in a photon into a particle-antiparticle pair, like: γ → e – + e + (3) A Feynman diagram, named after the American physicist Richard Feynman (1918–1988), may depict destruction or formation, as depicted in Figure 4.3. The formation of an electron-positron pair is seen in Figure 4.3(a). Elementary Particle Physics 93 Figure 4.3. Particle creation and annihilation.

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