Physics
Quark Physics
Quark physics is the study of subatomic particles called quarks, which are fundamental constituents of matter. Quarks are never found in isolation but are always bound together in composite particles such as protons and neutrons. The study of quark interactions and properties is a key focus of particle physics, providing insights into the fundamental forces and structure of matter.
Written by Perlego with AI-assistance
Related key terms
1 of 5
10 Key excerpts on "Quark Physics"
eBook - ePubAndrei Sakharov: Quarks And The Structure Of Matter
Quarks and the Structure of Matter
- Harry J Lipkin(Author)
- 2013(Publication Date)
- WSPC(Publisher)
5The Building Blocks of Matter — What is a Quark?
To begin this chapter I should explain what a quark is, and why we are interested in them. The place to find out what a word means is the dictionary. But any dictionary will not do. You have to know the language. The word quark can be found in any German dictionary, and this is a typical example of what one finds there.Quark, m. curd, curds; slime, slush, filth; (fig.) trifle, rubbish, trash…… So why should anyone be interested in this kind of junk? Perhaps this chapter will explain it.Modern atomic physics began with the discovery in the early part of this century that matter which appears so solid and massive to the layman really consists mainly of empty space with tiny particles rushing around at very high speeds. Today we all know that matter is composed of atoms which look like the familiar picture of a miniature solar system with electrons orbiting around a nucleus. We also know that there are tremendous energies locked in the nucleus. But although scientists and engineers have learned how to release and to use some of this nuclear energy, they still do not understand the structure of the nucleus and the many peculiar particles that are found inside. These particles are much too tiny to be observed with the most powerful microscopes and can only be studied with machines called “High Energy Accelerators”. These machines produce beams of tiny particles moving at extremely high speeds. By studying what happens when these high speed particles collide with other particles physicists endeavor to unravel the secrets of their structure.The use of collisions between high speed particles to study the nature of matter was developed by Rutherford and enabled him to discover that the atom consisted of a tiny nucleus surrounded mainly by empty space, rather than being continuous and homogeneous as matter appears to the naked eye. Today physicists use the same technique to probe the interior of the nucleus, using beams of much higher energy particles. Sometimes such high energy collisions create new particles which were not known before. Physicists thought at first that these particles must be the fundamental building blocks out of which all matter is made. But by 1960 so many different new particles had already been discovered that physicists began to think that perhaps these particles were made from even tinier particles arranged in different ways. It was found that a large group of particles which had been discovered had properties which suggested that they were all made by putting together three basic building blocks, which were given the name “quarks”. Extensive searches for quarks were undertaken since then by physicists who had hoped to discover the ultimate building block from which all matter was made. But so far no isolated quarks have been found. Instead more and more other particles were discovered which all look as if they were in some way made out of quarks.
eBook - ePub- Brian R. Martin, Graham Shaw(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
3 Quarks and hadronsWe turn now to the strongly interacting particles – the quarks and their bound states, the hadrons. These also interact by the weak and electromagnetic interactions, although such effects can often be neglected compared to the strong interactions. To this extent we are entering the realm of ‘strong interaction physics’.Strong interactions are most familiar in nuclear physics, where the interactions of neutrons and protons are studied at relatively low energies of a few tens of MeV. However, in 1947 new types of hadrons, not present in ordinary matter, were discovered in cosmic rays by groups from the universities of Bristol and Manchester. To create these new particles required high energies, in accordance with Einstein's mass–energy relation E = mc2 , and as intense beams of particles of increasingly higher energies became available at accelerator laboratories, more and more hadrons were discovered. By the late 1960s several dozen were known, and some unifying theoretical framework was urgently needed to interpret this multitude of states if any progress was to be made. The result was the quark model. In 1964, Gell-Mann, and independently Zweig, noted that all the observed hadrons could be simply interpreted as bound states of just three fundamental spin-1/2 particles, together with their antiparticles. These particles were required to have fractional electric charges of 2/3 and − 1/3, in units of e, and were called quarks by Gell-Mann, who later cited the now famous quotation ‘Three quarks for Muster Mark’ in James Joyce's book Finnegans Wake.1In the following years, the success of the quark model grew ever more impressive as more and more states were discovered. Nonetheless, the existence of quarks as real particles, rather than convenient mathematical entities, was seriously doubted because all attempts to detect free quarks, or any other fractionally charged particles, met with failure. These doubts were subsequently removed in two ways. Firstly, a series of experimental results, starting in 1968 with the scattering of high-energy electrons from protons, showed the dynamical effects of individual quarks within the proton. These experiments will be described in Chapters 7 and 8. Secondly, a detailed theory of strong interactions was constructed, which both successfully described the experimental results and offered an explanation of why isolated free quarks could not be observed. This theory is called Quantum Chromodynamics (QCD
- Robert K Logan(Author)
- 2010(Publication Date)
- World Scientific(Publisher)
The charm quark and the top quark each have a charge of +2/3 e while the bottom quark has a charge of –1/3 e. 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 252 The Poetry of Physics and The Physics of Poetry 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.
eBook - PDF- Nelson Boli´var(Author)
- 2023(Publication Date)
- Arcler Press(Publisher)
The strong force is therefore created by quarks, and the force that holds neutrons and protons together in the nucleus is a manifestation of the interaction among quarks (Mattingly, 2005; Smolin, 2010). Why have quarks never been segregated unless they are the building blocks of all hadrons? The quark-quark force is similar to the elastic force F = kx described by Hooke’slaw. The force between the quarks is negligible for small values of the separation distance x, and the quarks are largely free to move about within the particle. When we disassociate the quarks across Elementary Particle Physics 107 a vast gap distance of x, although, the force becomes extremely high, to the point where the quarks may not be detached at all. The confinement of quarks is the name for this situation. Quarks may not depart from the particle in which they are components, hence they are never observed in isolation (Isham, 1995; De Aquino, 2002). Is there, however, any proof that quarks exist? Yes, it is correct. In 1978, experiments were carried out at DESY (Deutsches Elektronen-Synchrotron) in Hamburg, Germany, in the modern PETRA storing ring. In a head-on collision, positrons, and electrons with energies of 20 GeV each were shot at each other. The disintegration of the electron and its antiparticle, the positron, releases a tremendous amount of energy, which is used to create quarks. Exactly as expected, the experimenters discovered a sequence of “quark jets,” which were the decay byproducts of the quarks. (A quark jet is a group of hadrons that leave the interaction in a similar direction.) The presence of quarks was indirectly demonstrated by such quark jets. CERN as well as other accelerators have conducted similar tests (Gorelik, 1992; Rovelli, 2003). Gluons and quarks do not appear to be built up of smaller particles once they had been established at this time; they seem to be elementary.
eBook - PDF- Vern Ostdiek, Donald Bord(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Their challenge has been a formidable one because, according to prevailing theories, quarks are believed to be inescapably bound within hadrons by what is called the color force. Within each hadron, the color force is mediated by exchange particles called gluons, and the “strings” that confine the individual quarks com- prising the hadrons are called gluon tubes. (See Section 12.5 for more on gluons and the color force.) Remarkably, the force that binds the quarks actually gets stronger as the separation between the quarks in the hadrons r r increases! This coun- terintuitive property of the color force, called “asymptotic freedom,” was discov- v v ered by David Gross, H. David Politzer, and Frank Wilczek, who shared the 2004 Nobel Prize in physics for their work. Thus, the strong force that exists between hadrons is now revealed to be just a shadow of the “really strong force”—the y y Table 12.5 Some Properties of the Originally Proposed Quarks a Quark Electric Charge ( Q ) b Strangeness ( S ) u 1 2 3 0 d 2 1 3 0 s 2 1 3 2 1 u 2 2 3 0 d 1 1 3 0 s 1 1 3 1 1 a The quarks are all spin 1 2 particles. b These values are in units of the proton charge. Thus the charge of an up quark in SI units would be _ 2 3 + (1.6 3 10 2 19 C) 5 1.07 3 10 2 19 C. p – p – V – L 0 0 0 e – e – e + e + p g g Figure 12.18 A schematic reconstruction of some of the particle tracks shown in Figureuni00A012.17. Solid lines indicate the trajectories of charged particles, and dashed lines give the paths of neutral particles (which do not show on the original photograph). The formation and decay of the V 2 involve the following reactions: (1) K 2 1 p S V 2 1 K 1 1 K 0 ; (2) V 2 S J 0 1 H9266 2 . Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 12.4 Quarks: Order Out of Chaosuni00A0 487 color force—that permanently conceals the quarks inside their host hadrons.
eBook - PDF- Stephen Thornton, Andrew Rex, Carol Hood, , Stephen Thornton, Stephen Thornton, Andrew Rex, Carol Hood(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
The electromagnetic force is responsible for attracting the electrons to the nucleus, and the strong (nuclear) force is responsible for keeping neutrons and protons together in the nucleus. The definition of elementary particle has changed over the years. In particle physics, we refer to an elementary particle as having no known substructure. That is, it is not made of smaller particles. Particles such as neutrons and protons that were believed in the 1930s and 1940s to be “elementary particles” become just “particles.” Some of these particles are indeed crucial to our understanding of matter and of the forces that hold matter together. We see in this chapter that neutrons and protons are made up of even more funda- mental particles called quarks. Although quarks cannot be observed outside the nucleus, we believe they must exist in order to explain experimental data. How far can this division into smaller and smaller units of matter continue (see Figure 14.1)? 10 -7 m(One ten- millionth of a meter) 10 -9 m 10 -10 m Virus Molecule 1 100 1 10 10 -14 m 10 -15 m Atom Nucleus 1 10,000 Less than 10 -18 m Proton Quark 1 1000 1 10 Figure 14.1 Starting from a virus, the structure of matter can be divided into smaller and smaller entities down to the quark and to whatever lies beyond. Courtesy of Universities Research Association. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
530 Chapter 11 | Particle Physics and Cosmology This OpenStax book is available for free at http://cnx.org/content/col12067/1.4 Figure 11.15 (a) Eight types of gluons carry the strong nuclear force. The white gluons are mixtures of color-anticolor pairs. (b) An interaction between two quarks through the exchange of a gluon. As suggested by this example, the interaction between quarks in an atomic nucleus can be very complicated. Figure 11.16 shows the interaction between a proton and neutron. Notice that the proton converts into a neutron and the neutron converts into a proton during the interaction. The presence of quark-antiquark pairs in the exchange suggest that bonding between nucleons can be modeled as an exchange of pions. Figure 11.16 A Feynman diagram that describes a strong nuclear interaction between a proton and a neutron. In practice, QCD predictions are difficult to produce. This difficulty arises from the inherent strength of the force and the inability to neglect terms in the equations. Thus, QCD calculations are often performed with the aid of supercomputers. The existence of gluons is supported by electron-nucleon scattering experiments. The estimated quark momenta implied by these scattering events are much smaller than we would expect without gluons because the gluons carry away some of the momentum of each collision. Unification Theories Physicists have long known that the strength of an interaction between particles depends on the distance of the interaction. Chapter 11 | Particle Physics and Cosmology 531 For example, two positively charged particles experience a larger repulsive force at a short distance then at a long distance. In scattering experiments, the strength of an interaction depends on the energy of the interacting particle, since larger energy implies both closer and stronger interactions.
eBook - PDFUnderstanding The Universe: From Quarks To Cosmos (Revised Edition)
From Quarks to the Cosmos
- Donald Lincoln(Author)
- 2012(Publication Date)
- World Scientific(Publisher)
Late in 1964, the was discovered in a bubble chamber exper-iment at Brookhaven National Laboratory on Long Island in New York. This particle decayed in a way consistent with having three strange quarks and had a mass 140 MeV more than that carried by baryons with two strange quarks. Since the particle was predicted (and with very specific properties) before it was discovered, this was regarded as a singular triumph of the quark model. Concerns with the confinement hypothesis were put aside for the moment while physi-cists tried to work out the confinement mechanism. It is one of the ironies of modern physics that while the quark model had great explanatory and predictive power, even the archi-tects of the quark model initially did not think of quarks as actual constituents of the mesons and baryons. The quark model was just thought of as simply a mathematical organizing principle. However Gell-Mann and Zweig were more prescient than they knew. Experiments performed in the late 1960s could not free quarks from protons, but they did reveal that the proton had a small but finite size and that there appeared to be something inside the proton. The objects contained within a proton were poorly understood in the beginning, as their properties had not been measured. However, once their existence was proven, the objects were named “partons” as they were part of the proton. Initially it was not possible to iden-tify partons with quarks (although we are now able to prove this). At this point in our story, we do not have enough information to 122 u n d e r s t a n d i n g t h e u n i v e r s e properly discuss these ideas (we will resume this discussion towards the end of Chapter 4), but we can roughly understand this experi-ment by analogy. The early experiments accelerated an electron to high energies and aimed them at a chunk of material (often hydrogen cooled until liquefied).
eBook - PDF- Donald H. Perkins(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
1 Quarks and leptons 1.1 Preamble The subject of elementary particle physics may be said to have begun with the discovery of the electron 100 years ago. In the following 50 years, one new particle after another was discovered, mostly as a result of experiments with cosmic rays, the only source of very high energy particles then available. However, the subject really blossomed after 1950, following the discovery of new elementary particles in cosmic rays; this stimulated the development of high energy accelerators, providing intense and controlled beams of known energy that were finally to reveal the quark substructure of matter and put the subject on a sound quantitative basis. 1.1.1 Why high energies? Particle physics deals with the study of the elementary constituents of matter. The word ‘elementary’ is used in the sense that such particles have no known structure, i.e. they are pointlike. How pointlike is pointlike? This depends on the spatial resolution of the ‘probe’ used to investigate possible structure. The resolution is r if two points in an object can just be resolved as separate when they are a distance r apart. Assuming the probing beam itself consists of pointlike particles, the resolution is limited by the de Broglie wavelength of these particles, which is λ = h / p where p is the beam momentum and h is Planck’s constant. Thus beams of high momentum have short wavelengths and can have high resolution. In an optical microscope, the resolution is given by r λ/ sin θ where θ is the angular aperture of the light beam used to view the structure of an object. The object scatters light into the eyepiece, and the larger the angle of scatter θ and the smaller the wavelength λ of the incident beam the better is the resolution. For example an ultraviolet microscope has better resolution and reveals 1 2 1 Quarks and leptons more detail than one using visible light.
eBook - PDF- Palash B. Pal(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
We will discuss elementary particles, and the next level of structures formed by them. For example, we will study interactions of the electron and its antipar-ticle, the positron. We can also discuss the positronium system, which is a bound state of an electron and a positron. We will study protons, because they are the first level structures formed from quarks. In fact, the proton is just an example of the class of structures known, as mentioned earlier, as hadrons. There are many hadrons, which can be broadly divided into two classes. Hadrons which have half-integral spin, e.g., the proton and the neu-tron, fall into the class called baryons . Hadrons with integral spin, like the pion, are called mesons . In other words, baryons are fermions, mesons are bosons. We will encounter many kinds of hadrons and discuss their properties in this book. 6 Chapter 1. Scope of particle physics But a hydrogen atom will not fall within the purview of particle physics, because that is a bound state of the electron and the proton, and the latter itself is a bound state of elementary quarks. Even nuclei are not included in discussions of particle physics, because they are bound states of protons and neutrons, neither of which is elementary. We will make exception to this rule only in a few places in the book when deuterium, tritium and helium nuclei will make their appearances in our discussions. However, even in such places, the aim will not be so much to understand the properties of those bound states, but rather to illustrate some general principles that apply to elementary particles as well. To summarize then, we will study the properties of elementary particles as well as the first level of structures formed by them. There are two kinds of properties associated with any system. The first kind can be called static properties, which the system possesses even if it is left alone.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
