◄UNIT 6 BLOCK DIAGRAM OF TELECOMMUNICATIONUNIT 8: PROPERTIES AND BASIC PRINCIPLES OF QUARKS ►

UNIT 7 NATURE OF PARTICLES AND THEIR INTERACTIONS

  • UNIT 7 NATURE OF PARTICLES AND THEIR INTERACTIONS

    Key unit competence: Organize the properties and basic principles of quarks.
    My goals
    • The key varieties of fundamental subatomic particles and how they
    were discovered.
    • Distinguish between fundamental particles and composite particles
    • Distinguish between particles and antiparticles
    • Describe how antimatter can be used as a source of energy
    • State some applications for elementary particles
    • Compare matter and antimatter
    • The four ways in which subatomic particles interact with each other.
    • Analyze the structure of protons, neutrons, and other particles can be

    explained in terms of quarks

    INTRODUCTORY ACTIVITY

    Investigating the elementary particles discovery
    In the study of matter description and energy as well as their interactions;
    the fascinating thing of discovery is the structure of universe of unknown
    radius but still to know the origin of matter one need to know about small
    and smallest composites of matter. The smallest particle was defined to be
    electron, proton, and neutron. But one can ask:
    1. Are electron, proton and neutron the only particle that can define the
    origin of matter?
    2. What are other particles matter is composed of?

    3. Describe and discuss how particles interact with energy to form matter

    7.1 ELEMENTARY PARTICLES.
    7.1.1 Introduction
    ACTIVITY 7.1: Investigate the presence of smaller particles
    1. Use internet and retrieve the definition and the information about
    elementary particles, and then answer to the following questions.
    2. What does elementary particle physics talk about?
    3. What are the elementary particles found through your research?
    4. Discuss and explain the use of knowledge about the elementary

    particles.

    Particle physics, also known as high-energy physics, is the field of natural
    science that pursues the ultimate structure of matter.
    The protons and neutrons are collectively called hadrons, were considered
    as elementary particles until 1960. We now know that they are composed of
    more fundamental particles, the quarks. Electrons remain elementary to
    this day. Muons and τ-leptons, which were found later, are nothing but heavy
    electrons, as far as the present technology can tell, and they are collectively
    dubbed leptons.
    Quarks and leptons are the fundamental building blocks of matter. The
    microscopic size that can be explored by modern technology is nearing

    . The quarks and leptons are elementary at this level (Nagashima, 2013).

    Particle physics is the study of the fundamental constituents of matter and
    their interactions. However, which particles are regarded as fundamental have
    changed with time as physicists’ knowledge has improved. Modern theory called
    the standard model attempts to explain all the phenomena of particle physics
    in terms of the properties and interactions of a small number of particles of
    three distinct types (see Fig.7.1):
    • Two families of fermions (of spin ½): leptons and quarks

    • One family of bosons (of spin 1)

    Fig.7. 1 Fundamental Standard model of elementary particle

    I, II and III represent the first, second and the third generations. In addition,
    at least one spin-0 particle, called the Higgs boson, is postulated to explain the
    origin of mass within the theory, since without it all the particles in the model
    are predicted to have zero mass (see Fig.7.1).

    All the particles of the standard model are assumed to be elementary; i.e. they
    are treated as point particles, without internal structure or excited states. The
    most familiar example of a lepton is the electron (the superscript denotes the
    electric charge), which is bound in atoms by the electromagnetic interaction,
    one of the four fundamental forces of nature. A second well-known lepton is
    the electron neutrino, which is a light, neutral particle observed in the decay
    products of some unstable nuclei (the so-called β-decays). The force responsible

    for the β-decay of nuclei is called the weak interaction.

    7.1.2 Checking my progress

    1. Particles that make up the family of Hadrons are:
    a. Baryons and mesons                                 c. Protons and electrons
    b. Leptons and baryons                                d. Muons and Leptons
    2. Using the elementary particles, Complete the following sentences
    I. One family of bosons of spin 1 called__________ which act as ‘force
    carriers’ in the theory
    II. Two fermions of spin 1/2 called_________ and ________
    3. The first antiparticle found was the
    a. Positron                                        c. Quark
    b. Hyperons                                     d. baryon

    4. Explain what is meant by particle physics?

    7.2 CLASSIFICATION OF ELEMENTARY PARTICLES.
    ACTIVITY 7.1: Classes of elementary particles
    Based on the previous introduction section, reread the text and the
    answer to the following questions.
    1. What are the types of elementary particles?

    2. What properties are based on to classify elementary particles?

    There are three properties that describe an elementary particle ‘’mass,’’
    ‘’charge’’ and ‘’spin’’. Each property is assigned as number value. These
    properties always stay the same for an elementary particle.
    • Mass (m): a particle has mass if it takes energy to increase its speed or
    to accelerate it. The values are given in MeV/C2
    . This comes from special
    relativity, which tells us that energy equals mass times the square of
    the speed of light. 2 E mc = × . All particles with mass are affected by
    gravity even particles with no mass like photon.
    • Electric charge (Q): particles may have positive, negative charge or
    none. If one particle has a negative charge and another particle has a
    positive, the two particles are attracted to each other. If particles have
    a similar charge, they repel each other. At a short distance this force
    is much stronger than the force of gravity which pulls all particles
    together. An electron has a charge -1 and a proton has a charge +1. A
    neutron has average charge 0. Normal quarks have charge of 2/3 or

    -1/3

     Spin: the angular momentum or constant turning of particles has a
    particular value, called its spin number. Spin for elementary particle
    is 0, 1 or . The spin property only donates the presence of angular

    momentum. 

    7.2.1 Classification of particles by mass
    The most basic way of classifying particles is by their mass. The heaviest
    particles are the hadrons and the lightest one is the leptons.

    As seen the diagram above hadrons group is divided into baryons and mesons.

    Baryons are the heaviest particles and are followed by mesons.
    Hadrons are composite particles made of quarks held together by the strong
    force in a similar way as molecules are held together by electromagnetic force.
    They are subjected to the strong nuclear force and are not fundamental particles

    as they are made up of quarks. 

     Baryons are composite sub-atomic particle made up of 3 quarks
     (triquarks are distinct from mesons which are composed of one quark and
    one antiquark). Baryon comes from Greek word which means “heavy”.
    The protons are only stable baryons; all other baryons eventually decay

    into proton. 

    Ex: Protons and neutrons.
    • Mesons are hadrons sub-atomic particles made up of one quark and

    one anti-quark bound together by strong interaction. Ex: Pion and kaon
    Each pion has quark and one anti-quark therefore is a meson. 
    It is the lightest meson and generally the lightest hadrons. They are unstable.


    Leptons do not interact via the strong force. They carry electric charge also interact

    via the weak nuclear force. They include electron, muons, tau and three the types
    of neutrino: the electron neutrino (νE), the muon neutrino (νμ
    ) and the tau neutrino
    egg vτ . 


    In summary, leptons are subjected to the weak nuclear force and they do not
    feel the strong nuclear force.
    Examples: Electron, muons and neutrino.



    7.2.2 Classification of particles by spin.



    The spin classification determines the nature of energy distribution in a
    collection of particles. Particles of integer spin obey Bose-Einstein statistics
    whereas those of half-integer spin behave according to Fermi-Dirac statistics
    as shown in the following chart




    Fermions are particles which have half-integer spin and therefore are
    constrained by the Pauli Exclusion Principle (see Section 7.4). It includes
    electrons, protons and neutrons.



    The fact that electrons are fermions is foundational to the buildup of the
    periodic table of elements since there can be only one electron for each state
    in an atom (only one electron for each possible set of quantum numbers).
    The fermion nature of electrons also governs the behavior of electrons in a
    metal where at low temperatures all the low energy states are filled up to a
    level called the Fermi energy. This filling of states is described by Fermi-Dirac
    statistics.



    7.2.3 Checking my progress







    7.3 ANTI PARTICLE AND PAULI’S EXCLUSION PRINCIPLE

    7.3.1 Concept of particle and antiparticle
    ACTIVITY 7.3
    Discuss the following terms:
    1. Particle
    2. Antiparticle

    There are two important points about pair production. The first is that you need
    to collect energy to produce the electron-positron pair. You need the equivalent
    rest mass of energy that is the amount of energy contained in the both particle
    and anti-particle when at rest. The energy converted to mass is ‘lost’ or fully
    ‘’bound’’ until the particle is annihilated and the energy can be recovered. The
    second thing is that it needs a correct environment. The process does not occur
    unless certain conditions are present.


    Viewing the phenomena as a creative process we can say a threshold amount

    of energy is sacrificed in a correct context to manifest a pair of particle with
    a physical mass. It can be said something was created out of nothing. That is 
    before the interaction, no particles with mass existed. After interaction, there
    were two particles with mass. Hence something was created out of nothing.
    But this can be said only because of the perspective taken when viewing the
    process.


    For every charged particle of nature, whether it is one of the elementary

    particles of the standard model, or a hadron, there is an associated particle
    of the same mass, but opposite charge, called its antiparticle. 



    This result is a necessary consequence of combining special relativity with

    quantum mechanics. This important theoretical prediction was made by Dirac
    and follows from the solutions of the equation he first wrote down to describe
    relativistic electrons


    7.3.2 Pauli’s exclusion principle,

    Pauli’s exclusion principle is a quantum mechanical principle which states
    that:
    “Two or more identical fermions (particles with half-integer spin) cannot
    occupy the same quantum state simultaneously.”




    In case of electrons in atoms it can be stated as follows: it is impossible for two
    electrons of a poly-electron atom to have the same values of the four quantum
    numbers:


    The principle quantum number No, the angular momentum quantum number
    (l), the magnetic quantum number (ml) and the spin quantum number (ms). 


    For example, if two electrons reside in the same orbital and if their msmust be
    different and thus like electrons must have opposite half integer spin projections 


    This principle was formulated by Austrian physicist Wolfgang Pauli in 1925 for
    electrons, and later extended to all fermions with his spin–statistics theorem of
    1940.


    Particles with an integer spin, or bosons, are not subject to the Pauli Exclusion
    Principle: any number of identical bosons can occupy the same quantum state,
    for instance, photons produced by a laser and Bose–Einstein condensate.


    The Pauli Exclusion Principle describes the behavior of all fermions (particles
    with “half-integer spin”), while bosons (particles with “integer spin”) are
    subject to other principles. Fermions include elementary particles such 


    7.3.3 Checking my progress
    1. What do you understand by antiparticle?
    2. State Pauli’s exclusion principle?
    3. Why Pauli’s exclusion Principle is known as exclusion?

    7.4 FUNDAMENTAL INTERACTIONS BY PARTICLE EXCHANGE
    ACTIVITY 7.4: Fundamental interaction

    Using internet, discusses the fundamental interactions in terms of
    exchange particles, then find the relation between the following concepts.
    1. Gravitational forces
    2. electroweak force,
    3. Strong force and
    4. Weak forces. 

    7.4.1 Forces and Interactions


    have recognized three basic forces:











    • The gravitational force is an inherent attraction between two masses.
    Gravitational force is responsible for the motion of the planets and
    Stars in the Universe. It is carried by Graviton. By Newton’s law of
    gravitation, the gravitational force is directly proportional to the
    product of the masses and inversely proportional to the square of
    the distance between them. Gravitational force is the weakest force
    among the fundamental forces of nature but has the greatest large−
    scale impact on the universe. Unlike the other forces, gravity works
    In the 1860s, the Scottish physicist James Clerk Maxwell developed a theory
    that unified the electric andmagnetic forces into a single electromagnetic force.
    Maxwell’s electromagnetic force was soon found to be the “glue” holding atoms,
    molecules, and solids together. It is the force between charged particles such
    as the force between two electrons, or the force between two current carrying
    wires. It is attractive for unlike charges and repulsive for like charges. The 
    universally on all matter and energy, and is universally attractive

    • The electric force is a force between charges
    • The magnetic force, which is a force between magnets or between
    magnetic body and ferromagnetic body.
    electromagnetic force obeys inverse square law. It is very strong compared
    to the gravitational force. It is the combination of electrostatic and magnetic forces.

    The discovery of the atomic nucleus, about 1910, presented difficulties that
    could not be explained by either gravitational or electromagnetic forces.
    The atomic nucleus is an unimaginably dense ball of protons and neutrons.
    But what holds it together against the repulsive electric forces between the
    protons? There must be an attractive force inside the nucleus that is stronger
    than the repulsive electric force. This force, called the strong force, is the force
    that holds the protons and neutrons together in the nucleus of an atom. It is the
    strongest of all the basic forces of nature. It, however, has the shortest range,
    of the order of 10−15 m. This force only acts on quarks. It binds quarks together
    to form baryons and mesons such as protons and neutrons. The strong force is
    mediated or carried by Gluons. Quarks carry electric charge so they experience

    electric and magnetic forces.

    In the 1939, physicists found that the nuclear radioactivity called beta decay
    could not be explained by either the electromagnetic or the strong force. Careful
    experiments established that the decay is due to a previously undiscovered
    force within the nucleus. The strength of this force is less than either the strong
    force or the electromagnetic force, so this new force was named the weak
    force. Weak nuclear force is important in certain types of nuclear process such
    as β-decay. This force is not as weak as the gravitational force. The weak force
    acts on both leptons and quarks (and hence on all hadrons). The weak force is
    carried by W+, W- and Z. Leptons – the electrons, muons and tau – are charged

    so they experience electric and magnetic forces.

    Of these, our everyday world is controlled by gravity and electromagnetism. The
    strong force binds quarks together and holds nucleons (protons & neutrons)
    in nuclei. The weak force is responsible for the radioactive decay of unstable

    nuclei and for interactions of neutrinos and other leptons with matter. 

    By 1940, the recognized forces of nature (fundamental forces)were four:
    • Gravitational forces between masses,
    • Electromagnetic forces resulting from the combination of electric and
    magnetic fields,
    • Strong force (nuclear force) between subatomic particles,
    • Weak forces that arise in certain radioactive decay processes.

    By 1980, Sheldon Glashow, Abdus Salam, and Steven Berg developed a theory
    that unifies electromagnetism and weak force into electroweak force. Hence, 

    our understanding of the forces of nature is in terms of     three fundamental

    forces: 

    • The gravitational force,
    • The electroweak force,

    • The strong force. 

    The Table 7.1 below summaries the fundamental forces and force carriers.



    • W boson: short-lived elementary particle; one of the carriers of the
    weak nuclear force
    • Z boson: short-lived elementary particle; one of the carriers of the
    weak nuclear force
    • Graviton: the hypothetical particle predicted to carry the gravitational

    force

    All the forces of nature should be capable of being described by single theory.
    But only at high energies should be the behavior of the forces combines, this is
    called unification. We can compare the relative strengths of the electromagnetic
    repulsion and the gravitational attraction between two protons of unit charge

    using the above equations.

    EXAMPLE 7.1


    Thus the gravitational is the weakest of the fundamental forces. These

    interactions and their relative strengths are summarized in Table 7.1

    7.4.2 Checking my progress

    1. Particles that interact by the strong force are called:
    a. Leptons                               c. Muons
    b. hadrons                             d. Electrons

    2. Name the four fundamental interaction and the particles that mediate each

    7.5 UNCERTAINTY PRINCIPLE AND PARTICLE CREATION

    7.5.1 The concept of uncertainty principle

    ACTIVITY 7.5: Investigation of particle creation and position.

    Basing on the knowledge and skills obtained from the previous sections
    of this unit, use internet to find the meaning of the particle creation.
    a. Is it possible to know the exact location of an elementary particle?

    b. Discuss and explain your findings

    The discovery of the dual wave–particle nature of matter forces us to re-evaluate

    the kinematic language we use to describe the position and motion of a particle.

    In classical Newtonian mechanics we think of a particle as a point. We can
    describe its location and state of motion at any instant with three spatial
    coordinates and three components of velocity. But because matter also has a
    wave aspect, when we look at the behaviour on a small enough scale comparable
    to the de Broglie wavelength of the particle we can no longer use the Newtonian
    description. Certainly no Newtonian particle would undergo diffraction like

    electrons do.

    To demonstrate just how non Newtonian the behaviour of matter can be, let’s
    look at an experiment involving the two-slit interference of electrons (Fig.7.4).
    We aim an electron beam at two parallel slits, just as we did for light. (The
    electron experiment has to be done in vacuum so that the electrons don’t collide

    with air molecules.) 

    What kind of pattern appears on the detector on the other side of the slits?

    The answer is: exactly the same kind of interference pattern we saw for photons.
    Moreover, the principle of complementarily, tells us that we cannot apply the
    wave and particle models simultaneously to describe any single element of
    this experiment. Thus we cannot predict exactly where in the pattern (a wave
    phenomenon) any individual electron (a particle) will land. We can’t even ask
    which slit an individual electron passes through. If we tried to look at where the
    electrons were going by shining a light on them that is, by scattering photons
    off them the electrons would recoil, which would modify their motions so that

    the two-slit interference pattern would not appear.

    Just as electrons and photons show the same behaviour in a two-slit interference
    experiment, electrons and other forms of matter obey the same Heisenberg

    uncertainty principles as photons do:

    Heisenberg uncertainty principle for position and momentum is given by

    This is a mathematical statement of the Heisenberg uncertainty principle Or
    it is sometimes called, the indeterminacy principle. It tells us that we cannot
    measure both the position and momentum of an object precisely at the same

    time.

    The uncertainty principle relates energy and time, examining this as follows.
    The object to be detected has an uncertainty in position   the photon that
    detects it travels with speed c, and it takes a time to pass through

    the distance of uncertainty. 

    7.5.2 Checking my progress

    1. The idea of uncertainty is used in many contexts; social, economic
    and scientific. People often talk about uncertain times, and when you
    perform a measurement you should always estimate the uncertainty
    (sometimes called the error). In physics the Heisenberg Uncertainty
    relation has a very specific meaning.

    a. Write down the Heisenberg uncertainty relation for position and
    momentum.
    b. Explain its physical significance.
    c. Does the Heisenberg uncertainty principle need to be considered
    when calculating the uncertainties in a typical first year physics
    experiment? Why or why not?
    d. Discuss the following statement: the uncertainty principle places a
    limit on the accuracy with which a measurement can be made. Do
    you agree or disagree, and why?
    2. An electron is confined within a region of width 11 5 10 m − × (Roughly
    the Bohr radius)
    a. Estimate the minimum uncertainty in the component of the
    electron’s momentum.
    b. What is the kinetic energy of an electron with this magnitude of
    momentum? Express your answer in both joules and electron

    volts.

    7.6 MATTER AND ANTIMATTER (PAIR PRODUCTION AND
    ANNIHILATION)

    ACTIVITY 7.5: Describing the matter and antimatter

    Use internet to describe the following concepts:
    1. Matter and give examples of matter particles
    2. Antimatter and give examples of antimatter particles
    3. Pair production
    4. Annihilation

    7.6. 1 Introduction

    Matter is a substance that has mass and takes up a space by having a volume. This
    include atoms and anything made up of these but no other energy phenomena
    or wave such as light or sound. Everything around you is made up of matter
    and is composed of particles including the fundamental fermions (quarks, 
    leptons, antiquarks and antileptons) which generally are matter particles and

    antimatter particles.

    Antimatter is a material composed of the antiparticle to the corresponding
    particle or ordinary particles. In theory a particle and its antiparticle have the
    same mass as one another but opposite electric charge and other differences in
    quantum numbers. Neutrons have antineutrons, electrons have positrons and
    neutrons have antineutrons as their respective antimatter. It was once thought
    that matter would neither be created nor destroyed. We know that energy and

    mass are interchangeable.

    7.6.2 Pair production and annihilation

    Pair production is a crucial example that photon energy can convert into
    kinetic energy as well as rest mass energy. Schematic diagram about the process
    of pair production is shown in Fig.7.5. The high-energy photon that has energy
    hf loses its entire energy when it collides with nucleus. Then, it makes pair of

    electron and positron and gives kinetic energy to each particle.

    Annihilation: When a particle collides with its antiparticle, the two annihilate
    each other with their mass being entirely converted into energy by the process
    called ‘’Annihilation’’

    These particles and anti-particles can meet each other and annihilate one
    another (See Fig.7.6). In each case the particle and its antiparticle annihilate
    each other, releasing a pair of high energy gamma photons.

    In this example, a proton and an anti-proton meet each other and annihilate,
    producing high energy gamma rays in the form of photons. Rest mass, charge,
    momentum and energy are conserved. They can also be produced from a high

    energy photon, this is called pair production.

    7.6.3 Application of antimatter
    Antimatter as a form of antiparticle of sub atomic particles has a variety of
    applications:
    • Positron emission tomography can be used to potentially treat cancer.
    • Stored antimatter can be used for interplanetary and inter stellar
    travel.
    • Antimatter reactions have practical applications in medical energy.
    • Antimatter has been considered as a trigger mechanism for nuclear
    weapons because whenever antimatter meets its corresponding
    matter the energy is released by annihilation.

    7.6.4 Checking my progress
    1. Antimatter as a form of sub atomic particles
    a. Electron
    b. proton
    c. matter
    d. antiparticle
    e. none of them is correct
    2. The process in which a particle and antiparticle unite annihilate each
    other and produce one or more photons is called………
    3. What happens when matter and antimatter collide?

    4. Compare matter and antimatter

    END UNIT ASSESSMENT 7
    A. Multiple choices
    1. The positron is called the antiparticle of electron, because it
    a. Has opposite charge and Annihilates with an electron
    b. Has the same mass
    c. Collides with an electron
    d. Annihilates with an electron
    2. Beta particles are
    e. Neutrons
    f. Protons
    g. Electrons
    h. Thermal neutrons
    3. If gravity is the weakest force, why is it the one we notice most?
    a. Our bodies are not sensitive to the other forces.
    b. The other forces act only within atoms and therefore have no
    effect on us.
    c. Gravity may be “very weak” but always attractive, and the
    Earth has enormous mass. The strong and weak nuclear
    forces have very short range. The electromagnetic force has a
    long range, but most matter is electrically neutral.
    d. At long distances, the gravitational force is actually stronger
    than the other forces.
    e. The other forces act only on elementary particles, not on
    objects our size.
    B. Structured questions
    4. According to the classification of elementary particles by mass.

    Complete the following figure

    5.
    I. State two differences between a proton and a positron.
    II. A narrow beam of protons and positrons travelling at the same
    speed enters a uniform magnetic field. The path of the positrons
    through the field is shown in Fig.7.7. Sketch on this figure the

    path you would expect the protons to take.

    III. Explain why protons take a different path to that of the
    positrons.
    6. A positron with kinetic energy 2.2 MeV and an electron at rest
    annihilate each other. Calculate the average energy of each of the
    two gamma photons produced as a result of this annihilation.
    C. Essay question
    7. Describe briefly the following particle-terms terms: π -meson,

    muon, neutrino, antiparticle, hadrons and lepton.

    ◄UNIT 6 BLOCK DIAGRAM OF TELECOMMUNICATIONUNIT 8: PROPERTIES AND BASIC PRINCIPLES OF QUARKS ►