Leptons And Quarks (Special Edition Commemorating The Discovery Of The Higgs Boson)

(Special Edition Commemorating the Discovery of the Higgs Boson)

Lev B Okun

• Publisher: WSPC
• Year: 2014
• ISBN:
  9789814603140
• Topic: Ciencias biológicas
• Subtopic: Ciencias en general

The book “Leptons and Quarks” was first published in the early 1980s, when the program of the experimental search for the intermediate bosons W and Z and Higgs boson H was formulated. The aim and scope of the present extended edition of the book, written after the experimental discovery of the Higgs boson in 2012, is to reflect the various stages of this 30+ years search. Along with the text of the first edition of “Leptons and Quarks” it contains extracts from a number of books published by World Scientific and an article from “On the concepts of vacuum and mass and the search for higgs” available from http://www.worldscientific.com/worldscinet/mpla or from http://arxiv.org/abs/1212.1031.

The book is unique in communicating the Electroweak Theory at a basic level and in connecting the concept of Lorenz invariant mass with the concept of the Extended Standard Model, which includes gravitons as the carriers of gravitational interaction.

Contents:

• Introduction
• Structure of Weak Currents
• Muon decay
• Strangeness-Conserving Leptonic Decays of Hadrons. Properties of the Ud-Current
• Leptonic Decays of Pions and Nucleons
• Leptonic Decays of K-Mesons and Hyperons
• Strangeness-Changing Non-Leptonic Interactions
• Phenomenology of Non-Leptonic Interactions
• Dynamics of Non-Leptonic Decays of Hyperons
• Non-Leptonic Decays of K-Mesons
• Neutral K-Mesons in Vacuum and in Matter
• Violation of CP Invariance
• Decays of the τ-Lepton
• Decays of Charmed Particles
• Weak Decays b- and t-Quarks
• Neutrino–Electron Interactions
• Neutrino–Nucleon Interactions
• Renormalizability
• Gauge Invariance
• Spontaneous Symmetry Breaking
• Standard Model of the Electroweak Interaction
• Neutral Currents
• Properties of Intermediate Bosons
• Properties of Higgs Bosons
• Grand Unification
• Superunification
• Particles and the Universe
• Bibliography
• Apendix (Some Useful Formulas)
• Tables of Experimental Data

Readership: Graduate students and researchers in high energy and particle physics.

CHAPTER 1

Introduction

The weak interaction is responsible for a large number of physical processes: nuclear β-decay, numerous decays of elementary particles, reactions induced by neutrinos from accelerators and nuclear reactors, and also some subtle effects involving parity violation in γ-decays of nuclei and in atomic optical spectra. All known leptons and hadrons are subject to the weak interaction. It plays an important role in such astrophysical phenomena as the sun’s burning and supernova explosions. Some of the weak processes were already put to use (for example, the angular asymmetry in the muon decay is a promising new tool in chemistry). Mainly, however, our interest in the weak interaction is rooted not in its possible applications but in the hope that its study will ultimately yield a unified theory of elementary particles and of the interactions between them. And although it would be very difficult today to predict any practical consequences of such a unified theory, there can be no doubt of their utmost importance.

In contrast to “stronger” interactions, namely the strong and electromagnetic, the weak interaction violates a number of conservation laws. Among the quantum numbers that are not conserved are space parity P, charge conjugation parity C, combined inversion parity CP, strangeness, charm, and some others.

The standard theory of weak interactions is based on the analogy with the electromagnetic interaction which is produced by the electromagnetic current coupled to the photon (see fig. 1.1). Likewise, the weak interaction is postulated to result from weak currents being coupled to the so-called intermediate bosons W⁺, W⁻, Z. Intermediate bosons have not yet been found experimentally; however, this does not point to a defect in the theory since the expected masses are of the order of 100 GeV, the energies of the existing accelerators being well below their production thresholds. The W⁺ and W⁻ bosons are coupled to charged currents which change the charges of particles involved. Such are the currents

and their hermitian conjugate currents

The last two currents, for instance, interact by exchanging a virtual W-boson and yield the muon decay

(fig. 1.2). The Z⁰ bosons are created by neutral currents of the types

and so on, involving identical ingoing and outgoing particles. Neutral currents are responsible, for example, for the scattering v_μe → v_μe (fig. 1.3). Both the charged and the neutral currents include a leptonic and a hadronic part. At present we know six leptons which are naturally grouped into three pairs:

Fig. 1.1.

so that each lepton has its neutrino counterpart. Each lepton enters the charged current j with the appropriate neutrino:

This current emits W⁺ bosons and absorbs W⁻ bosons. The hermitian conjugate current

emits W⁻ bosons and absorbs W⁺ bosons. The neutral leptonic current

contains six terms:

The two leptonic currents given above are responsible for the processes involving both leptons

and antileptons

This follows from the properties of the relevant operators. For example, the operator ē creates an electron and annihilates a positron, while the operator e creates a positron and annihilates an electron. Operators of other particles act in a similar manner.

Fig. 1.2.

Fig. 1.3.

1.1. Quark currents

Hadrons are represented in weak currents by quarks. According to quark theory, all known hadrons consist of quarks of five types (five flavors): u, d, s, c and b. Theoretical arguments, however, point to the existence of a sixth quark t, so that in analogy to the six leptons, the six quarks form three pairs:

We recall that the charges of quarks u, c, and t are

and those of quarks d, s, and b are

The quark structure is uud for the proton, udd for the neutron,

for the π⁺ meson, and so on. Strange particles include s-quarks (for instance,

), and charmed particles include c-quarks (for example,

). Particles with hidden charm, such as the J/ψ meson, are represented by

The structure of the T-meson is

No hadrons with single b-quarks have so far been found*, and only very scant indirect information is available on the weak interaction of the b- and t-quarks (se...