Physics
Classification of Particles
The classification of particles in physics is based on their properties and interactions. Particles can be classified as fermions or bosons based on their spin, and as elementary or composite based on their structure. The Standard Model of particle physics categorizes particles into six types of quarks, six types of leptons, and four types of gauge bosons.
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6 Key excerpts on "Classification of Particles"
eBook - PDF- SachchidaNand Shukla(Author)
- 2023(Publication Date)
- Arcler Press(Publisher)
CLASSIFICATION OF ELEMENTARY PARTICLES 2 CONTENTS 2.1. Classification According to Spin........................................................ 35 2.2. Fermion ............................................................................................ 36 2.3. Quarks.............................................................................................. 40 2.4. Lepton .............................................................................................. 43 2.5. Boson ............................................................................................... 44 2.6. Elementary Bosons............................................................................ 45 2.7. Higgs Boson ..................................................................................... 45 2.8. Photon .............................................................................................. 47 2.9. Gluon ............................................................................................... 49 2.10. W and Z Bosons ............................................................................. 49 2.11. Composite Bosons .......................................................................... 51 2.12. Classification According to Mass..................................................... 51 2.13. Classification According to Charge ................................................. 57 CHAPTER The Study of Elementary Particles 32 Particle physics (sometimes referred to as high physics) is the study of the constitution of particles that make up matter and radiation. Despite the fact that the term particle can apply to a variety of very small objects (such as electrons, gas particles, or even dust), particle physics usually focuses on the indivisibly tiniest measurable particles and the basic interactions that explain their behavior. These fundamental particles, according to present understanding, are excitations of the quantum fields which regulate their interactions.
eBook - PDF- Stephen Thornton, Andrew Rex, Carol Hood, , Stephen Thornton, Stephen Thornton, Andrew Rex, Carol Hood(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
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. 528 Chapter 14 Particle Physics 14.3 Classification of Particles As the number of known particles continued to increase in the 1950s and 1960s, physicists proposed various schemes to make sense of what some referred to as the particle “zoo.” Since the 1960s experimentalists have needed accelerators with ever-increasing energies in order to test elementary particle theories. Even- tually, an understanding of the zoo developed due to many contributions. In this section we present a compact picture of the organization of particles that repre- sents some of the most important advances in particle physics during the past 60 years. We discussed in Chapter 9 that particles with half-integral spin are called fermions and those with integral spin are called bosons. This is a particularly useful way to classify elementary particles because all stable matter in the universe appears to be composed, at some level, of constituent fermions. We have already discussed some bosons in the previous section. Photons, gluons, W 6 , and Z are called gauge bosons and are responsible for the strong and electroweak interactions. Gravi- tons are also bosons, having spin 2. Fermions exert attractive or repulsive forces on each other by exchanging gauge bosons, which are the force carriers. A “gauge” refers to a specific mathematical formalism that helps mathematicians and physicists deal with location in space and helps understand symmetries. Higgs Boson During the 1960s and 1970s the Standard Model of Particle Physics was becom- ing more widely accepted. The experimental discovery of the W 6 , Z bosons in 1983 heightened its success.
eBook - PDF- Kenneth S. Krane(Author)
- 2020(Publication Date)
- Wiley(Publisher)
The names originally given to these groups are based on the Greek words for light, middle, and heavy: leptons for the 14.2 Classifying Particles 467 light particles, mesons for the middle group, and baryons for the heavier particles. Even though the classification by mass is now obsolete (leptons and mesons have been discovered that are more massive than protons or neutrons), we keep the original names, which now describe instead a group or family of particles with similar properties. When we compare our first two ways of classifying particles, we find an interesting result: The leptons do not interact through the strong force, but the mesons and baryons do. We can also classify particles by their intrinsic spins. Every particle has an intrinsic spin; you will recall that the electron has a spin of 1 2 , as do the proton and neutron. We find that the leptons all have spins of 1 2 , the mesons all have integral spins (0, 1, 2, . . . ), and the baryons all have half-integral spins ( 1 2 , 3 2 , 5 2 , . . . ). Antiparticles One additional property that is used to classify a particle is the nature of its antiparticle. ∗ Every particle has an antiparticle, which is identical to the particle in such properties as mass and lifetime, but differs from the particle in the sign of its electric charge (and in the sign of certain other properties, as we discuss later). The antiparticle of the electron is the positron e + , which was discovered in the 1930s through reactions initiated by cosmic rays. The positron has a charge of +e (opposite to that of the electron) and a rest energy of 0.511 MeV (identical to that of the electron). The antiproton p was dis- covered in 1956 (see Example 2.21); it has a charge of −e and a rest energy of 938 MeV. A stable atom of antihydrogen could be constructed from a positron and an antiproton; the properties of this atom would be identical to those of ordinary hydrogen.
eBook - ePub- Britannica Educational Publishing, Erik Gregersen(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
CHAPTER 1 B ASIC C ONCEPTS OF P ARTICLE P HYSICS S ubatomic, or elementary, particles are various self-contained units of matter or energy that are the fundamental constituents of all matter. They include electrons, the negatively charged, almost massless particles that nevertheless account for most of the size of the atom, and they include the heavier building blocks of the small but very dense nucleus of the atom, the positively charged protons and the electrically neutral neutrons. But these basic atomic components are by no means the only known subatomic particles. Protons and neutrons, for instance, are themselves made up of elementary particles called quarks, and the electron is only one member of a class of elementary particles that also includes the muon and the neutrino. More unusual subatomic particles—such as the positron, the antimatter counterpart of the electron—have been detected and characterized in cosmic-ray interactions in the Earth’s atmosphere. The field of subatomic particles has expanded dramatically with the construction of powerful particle accelerators to study high-energy collisions of electrons, protons, and other particles with matter. As particles collide at high energy, the collision energy becomes available for the creation of subatomic particles such as mesons and hyperons. Finally, completing the revolution that began in the early 20th century with theories of the equivalence of matter and energy, the study of subatomic particles has been transformed by the discovery that the actions of forces are due to the exchange of “force” particles such as photons and gluons. More than 200 subatomic particles have been detected—most of them highly unstable, existing for less than a millionth of a second—as a result of collisions produced in cosmic-ray reactions or particle-accelerator experiments
eBook - PDFFrom Atoms to Galaxies
A Conceptual Physics Approach to Scientific Awareness
- Sadri Hassani(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
Chapter 33 Classifying Particles and Forces The invention of the accelerators in the 1930s and their rapid development after WWII opened up a new vista for fundamental physics research. The few particles that made themselves known in the early days of nuclear physics were only the tip of an iceberg. By the mid 1950s the accelerators produced so many new particles that physicists felt like eighteenth century zoologists facing a seemingly endless variety of “animals” to study. And just like the zoologists, they embarked on their classification. The initial key to this classification was the strength of the particles’ interaction with matter. By forcefully injecting the new particles into varying thicknesses of lead, physicists Hadrons and leptons. could identify two major categories of particles: those that were stopped quickly (i.e., after moving a short distance) were called hadrons 1 because they must have interacted with matter very strongly; the remaining particles, thought to be “lighter” than hadrons, were named leptons —derived from the Greek word for light. Another scheme of classifying particles, which was probably more important than their stopping distance in lead, was their half-life. With the exception of the proton, electron, neutrino, and their antiparticles, all known particles were unstable , i.e., they did not live forever. For example, a free neutron was known to decay into a proton, an electron, and an antineutrino in about 15 minutes. 2 Based on the length of their half-lives, particles’ interactions were divided into three categories: strong, weak, and electromagnetic. Particles partaking in the strong interaction had a very short half-life (of the order of 10 -20 s); those participating in the weak interaction had a long half life (of the order of 10 -6 s and longer); electromagnetic interaction was represented by an intermediate half-life. By definition, only hadrons took part in strong interactions.
eBook - PDF- Gary N. Felder, Kenny M. Felder(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
The first two sections of this chapter survey the overwhelming “zoo” of particles that emerged over decades of experiments, and the standard model that brought order to the chaos. If you want a general overview of particle physics, you could stop after those two sections. The third section fills in some of the experimental evidence that uncovered so many particles. The rest of the chapter explores topics like the strong force, conservation laws and symmetry, and quantum field theory: the theory we use to describe how all these particles interact. Along the way we’ll highlight some open questions and areas of active research in particle physics today. 13.1 Forces and Particles In this section we’re going to survey particle physics from the 1930s to the 1960s, a period marked by a dizzying proliferation of seemingly fundamental particles. In the next section we’ll see how the “standard model” of the 1960s and 1970s simplified the list down to roughly 20. 596 13.1 Forces and Particles 597 13.1.1 Explanation: Forces and Particles What defines a particular type of particle? That’s one of those questions that you’ve probably never bothered to ask. If you were sorting a set of blocks into different types, you might look at their shapes or their sizes or their colors. But an electron and a neutrino don’t have shapes, sizes, or colors. (Or smells or textures or patterns or specific heats or favorite football teams.) What makes them different particles? Active Reading Exercise: Different Types of Particles Consider two point particles. List all the properties you can think of that might distinguish these two particles, such that we would say that they are not the same type of particle. (With a bit of thought, you should be able to think of the three we list below.) Perhaps the most obvious property on the list is mass. Every electron has the same mass as every other electron.
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