What are Elementary Particles | Physics for EmSAT Achieve PDF Download

 Page 1


   
Elementary Particles Elementary Particles
Elementary Particles Elementary Particles   
Elementary Particles Elementary Particles
The term elementary particles signify the particles of structureless and those can The term elementary particles signify the particles of structureless and those can
not be constructed from other particles. not be constructed from other particles.
Present model of the constituents of matter is that they consist of fundamental Present model of the constituents of matter is that they consist of fundamental
point like, on a scale of 10 point like, on a scale of 10
-17 -17
  m, spin ½ fermions- the quarks with fractional   m, spin ½ fermions- the quarks with fractional
electric charge and the leptons carrying zero or integral electric charge. Hence electric charge and the leptons carrying zero or integral electric charge. Hence
there are two types of fundamental fermions, called quarks and leptons, which there are two types of fundamental fermions, called quarks and leptons, which
are structuresless and point like. are structuresless and point like.
One of the important modern ideas of forces is that forces between particles One of the important modern ideas of forces is that forces between particles
arise from the exchange of particles. arise from the exchange of particles.
Cl ssif atio of El me ta y a t c es Classification of Elementary Particles
   
The elementary particles are classified in terms of their mass, intrinsic spin, The elementary particles are classified in terms of their mass, intrinsic spin,
magnetic moment and interaction properties. magnetic moment and interaction properties.
The following table represents the list of The following table represents the list of such particles: such particles:
Elementary Particles Elementary Particles
Hadrons (Quarks) Hadrons (Quarks)
Baryon Baryon Photon Leptons Photon Leptons Mesons Mesons
Nucleon Hyperons Nucleon Hyperons
Photon Photon   
Photon Photon
The first member of elementary particles is gamma ray photons, which is an The first member of elementary particles is gamma ray photons, which is an
electromagnetic quantum. electromagnetic quantum.
• •   These particles take part These particles take part in electromagnetic interactions. in electromagnetic interactions.
• •   They have zero rest mass and zero spin. They have zero rest mass and zero spin.
• •   They are bosons. They are bosons.
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Elementary Particles Elementary Particles
Elementary Particles Elementary Particles   
Elementary Particles Elementary Particles
The term elementary particles signify the particles of structureless and those can The term elementary particles signify the particles of structureless and those can
not be constructed from other particles. not be constructed from other particles.
Present model of the constituents of matter is that they consist of fundamental Present model of the constituents of matter is that they consist of fundamental
point like, on a scale of 10 point like, on a scale of 10
-17 -17
  m, spin ½ fermions- the quarks with fractional   m, spin ½ fermions- the quarks with fractional
electric charge and the leptons carrying zero or integral electric charge. Hence electric charge and the leptons carrying zero or integral electric charge. Hence
there are two types of fundamental fermions, called quarks and leptons, which there are two types of fundamental fermions, called quarks and leptons, which
are structuresless and point like. are structuresless and point like.
One of the important modern ideas of forces is that forces between particles One of the important modern ideas of forces is that forces between particles
arise from the exchange of particles. arise from the exchange of particles.
Cl ssif atio of El me ta y a t c es Classification of Elementary Particles
   
The elementary particles are classified in terms of their mass, intrinsic spin, The elementary particles are classified in terms of their mass, intrinsic spin,
magnetic moment and interaction properties. magnetic moment and interaction properties.
The following table represents the list of The following table represents the list of such particles: such particles:
Elementary Particles Elementary Particles
Hadrons (Quarks) Hadrons (Quarks)
Baryon Baryon Photon Leptons Photon Leptons Mesons Mesons
Nucleon Hyperons Nucleon Hyperons
Photon Photon   
Photon Photon
The first member of elementary particles is gamma ray photons, which is an The first member of elementary particles is gamma ray photons, which is an
electromagnetic quantum. electromagnetic quantum.
• •   These particles take part These particles take part in electromagnetic interactions. in electromagnetic interactions.
• •   They have zero rest mass and zero spin. They have zero rest mass and zero spin.
• •   They are bosons. They are bosons.
   
2 2
Leptons Leptons   
Leptons Leptons
The second category of elementary particles is called lepton, which consists of The second category of elementary particles is called lepton, which consists of
light particles. light particles.
• •
   
They take part in electromagnetic and weak interactions and They take part in electromagnetic and weak interactions and
• •   They have half-odd integral spins. They have half-odd integral spins.
• •   They are fermions They are fermions
Types of leptons Types of leptons
There are two types of There are two types of leptons: leptons:
(a) (a)   Charged, and (b) Neutral. Charged, and (b) Neutral.
Charged leptons Charged leptons
The charged leptons are electron, The charged leptons are electron,  µ   µ  -meson or muon, and -meson or muon, and t  t  -lepton. These leptons -lepton. These leptons
occur in doublet that is positively and negatively charged. occur in doublet that is positively and negatively charged.
Neutral leptons Neutral leptons
The neutral leptons are known as neutrinos. They are neutral particles having The neutral leptons are known as neutrinos. They are neutral particles having
zero rest mass. zero rest mass.
There are three types of neutrinos associated with each type of lepton and There are three types of neutrinos associated with each type of lepton and
correspondingly called correspondingly called e e-neutrino and -neutrino and µ   µ  -neutrino -neutrino ? ?   t  t  -neutrino. -neutrino.
Electron Electron
Electrons are leptons, which are negatively charged stable particles. Their mass Electrons are leptons, which are negatively charged stable particles. Their mass
is about 5.48 x 10 is about 5.48 x 10
-4 -4
 amu.  amu.
Muon Muon
Muons are leptons, which are also negatively charged particles but heavier than Muons are leptons, which are also negatively charged particles but heavier than
electrons. Their mass is 207 times mass of electrons. They are characterized by electrons. Their mass is 207 times mass of electrons. They are characterized by
life of the order of 10 life of the order of 10
-6 -6
sec. sec.
Neutrinos Neutrinos
t  ton was first observed -lepton was first observed in accelerator experiments in 1974. in accelerator experiments in 1974.
Hadrons Hadrons
Hadrons Hadrons
These are the strongly interacting heavy particles. These are the strongly interacting heavy particles.
Types of Hadrons Types of Hadrons
They are classified into two types: Mesons and They are classified into two types: Mesons and Baryons. Baryons.
Mesons Mesons
These are particles heavier than electrons and lighter than nucleons. These are particles heavier than electrons and lighter than nucleons. Their mass Their mass
lies between 250 and 1000 times mass of lies between 250 and 1000 times mass of the electrons. the electrons.
• •
   
These particles have strong interaction with nuclear matter These particles have strong interaction with nuclear matter
• •    They are particles of nuclear field. They are particles of nuclear field.
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Elementary Particles Elementary Particles
Elementary Particles Elementary Particles   
Elementary Particles Elementary Particles
The term elementary particles signify the particles of structureless and those can The term elementary particles signify the particles of structureless and those can
not be constructed from other particles. not be constructed from other particles.
Present model of the constituents of matter is that they consist of fundamental Present model of the constituents of matter is that they consist of fundamental
point like, on a scale of 10 point like, on a scale of 10
-17 -17
  m, spin ½ fermions- the quarks with fractional   m, spin ½ fermions- the quarks with fractional
electric charge and the leptons carrying zero or integral electric charge. Hence electric charge and the leptons carrying zero or integral electric charge. Hence
there are two types of fundamental fermions, called quarks and leptons, which there are two types of fundamental fermions, called quarks and leptons, which
are structuresless and point like. are structuresless and point like.
One of the important modern ideas of forces is that forces between particles One of the important modern ideas of forces is that forces between particles
arise from the exchange of particles. arise from the exchange of particles.
Cl ssif atio of El me ta y a t c es Classification of Elementary Particles
   
The elementary particles are classified in terms of their mass, intrinsic spin, The elementary particles are classified in terms of their mass, intrinsic spin,
magnetic moment and interaction properties. magnetic moment and interaction properties.
The following table represents the list of The following table represents the list of such particles: such particles:
Elementary Particles Elementary Particles
Hadrons (Quarks) Hadrons (Quarks)
Baryon Baryon Photon Leptons Photon Leptons Mesons Mesons
Nucleon Hyperons Nucleon Hyperons
Photon Photon   
Photon Photon
The first member of elementary particles is gamma ray photons, which is an The first member of elementary particles is gamma ray photons, which is an
electromagnetic quantum. electromagnetic quantum.
• •   These particles take part These particles take part in electromagnetic interactions. in electromagnetic interactions.
• •   They have zero rest mass and zero spin. They have zero rest mass and zero spin.
• •   They are bosons. They are bosons.
   
2 2
Leptons Leptons   
Leptons Leptons
The second category of elementary particles is called lepton, which consists of The second category of elementary particles is called lepton, which consists of
light particles. light particles.
• •
   
They take part in electromagnetic and weak interactions and They take part in electromagnetic and weak interactions and
• •   They have half-odd integral spins. They have half-odd integral spins.
• •   They are fermions They are fermions
Types of leptons Types of leptons
There are two types of There are two types of leptons: leptons:
(a) (a)   Charged, and (b) Neutral. Charged, and (b) Neutral.
Charged leptons Charged leptons
The charged leptons are electron, The charged leptons are electron,  µ   µ  -meson or muon, and -meson or muon, and t  t  -lepton. These leptons -lepton. These leptons
occur in doublet that is positively and negatively charged. occur in doublet that is positively and negatively charged.
Neutral leptons Neutral leptons
The neutral leptons are known as neutrinos. They are neutral particles having The neutral leptons are known as neutrinos. They are neutral particles having
zero rest mass. zero rest mass.
There are three types of neutrinos associated with each type of lepton and There are three types of neutrinos associated with each type of lepton and
correspondingly called correspondingly called e e-neutrino and -neutrino and µ   µ  -neutrino -neutrino ? ?   t  t  -neutrino. -neutrino.
Electron Electron
Electrons are leptons, which are negatively charged stable particles. Their mass Electrons are leptons, which are negatively charged stable particles. Their mass
is about 5.48 x 10 is about 5.48 x 10
-4 -4
 amu.  amu.
Muon Muon
Muons are leptons, which are also negatively charged particles but heavier than Muons are leptons, which are also negatively charged particles but heavier than
electrons. Their mass is 207 times mass of electrons. They are characterized by electrons. Their mass is 207 times mass of electrons. They are characterized by
life of the order of 10 life of the order of 10
-6 -6
sec. sec.
Neutrinos Neutrinos
t  ton was first observed -lepton was first observed in accelerator experiments in 1974. in accelerator experiments in 1974.
Hadrons Hadrons
Hadrons Hadrons
These are the strongly interacting heavy particles. These are the strongly interacting heavy particles.
Types of Hadrons Types of Hadrons
They are classified into two types: Mesons and They are classified into two types: Mesons and Baryons. Baryons.
Mesons Mesons
These are particles heavier than electrons and lighter than nucleons. These are particles heavier than electrons and lighter than nucleons. Their mass Their mass
lies between 250 and 1000 times mass of lies between 250 and 1000 times mass of the electrons. the electrons.
• •
   
These particles have strong interaction with nuclear matter These particles have strong interaction with nuclear matter
• •    They are particles of nuclear field. They are particles of nuclear field.
   
3 3
• •    They have zero intrinsic spin, They have zero intrinsic spin,
• •    They are bosons. They are bosons.
Types of Mesons Types of Mesons
Mesons are divided into three groups: Mesons are divided into three groups: p p-Meson (pion), k-meson (kaon), and -Meson (pion), k-meson (kaon), and ? ?- -
meson. meson.
p  p  p p p  p  p  p  -Mesons -Mesons   
p  p  -Mesons are found to have three states of charge: -Mesons are found to have three states of charge:
(a) Positive, (a) Positive, p  p     
+ +
, , (b) (b) Negative, Negative, p  p     
- -
 and (c) Neutral,  and (c) Neutral, p  p     
0 0
. .
Positive Positive p  p  -meson has mass of 275 times mass of electrons and life of about 10 -meson has mass of 275 times mass of electrons and life of about 10
-2 -2
   
sec. sec.
Neutral Neutral p  p  -meson has mass of 264 times mass of the electron. -meson has mass of 264 times mass of the electron.
Neutral Neutral p  p     
0 0
  mesons are produced in the collision of protons having Kinetic   mesons are produced in the collision of protons having Kinetic
energy energy = = 150 MeV.  150 MeV. Similarly, in photoproduction of energetic gamma quanta, Similarly, in photoproduction of energetic gamma quanta, p  p     
+ +
- -mesons are produced. mesons are produced.
K-Mesons K-Mesons
K-Mesons are found to be in three charge states: K-Mesons are found to be in three charge states:
(a) Positive, (a) Positive, k  k   +  +, (b) Negative, , (b) Negative, k  k     
- -
, and (c) Neutral, , and (c) Neutral, k  k  0 0   
Positive k-meson has mass 966 times of the electronic mass. And that neutral Positive k-meson has mass 966 times of the electronic mass. And that neutral k  k  - -
mesons have 967 times electronic mass. mesons have 967 times electronic mass.
Baryons Baryons   
Baryons Baryons
These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons
are further grouped into two classes: are further grouped into two classes: (a) nucleon, and (b) hyperons. (a) nucleon, and (b) hyperons.
Nucleons are constituent particles of the nucleus of an atom. They are protons Nucleons are constituent particles of the nucleus of an atom. They are protons
and neutrons. Protons and neutrons have nearly equal mass. But protons are and neutrons. Protons and neutrons have nearly equal mass. But protons are
positively charged and neutrons are neutral. positively charged and neutrons are neutral.
Hyperons Hyperons   
Hyperons Hyperons
Hyperons are the particles heavier than nucleons. They are characterized by Hyperons are the particles heavier than nucleons. They are characterized by
their lifetime, which has the order of 10 their lifetime, which has the order of 10
-10 -10
  sec. The hyperons have strange   sec. The hyperons have strange
behavior that they decay faster than are behavior that they decay faster than are formed. formed.
Types of hyperons Types of hyperons
There are four types of hyperons: There are four types of hyperons:
? ?-hyperon, -hyperon, S S-hyperons, -hyperons, ? ?-hyperons and -hyperons and ? ?-hyperons. -hyperons.
? ?
-hyperons are neutral particles and so ar -hyperons are neutral particles and so are represented as e represented as
? ?
0 0
S S-hyperons exist in three charge states -hyperons exist in three charge states
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Elementary Particles Elementary Particles
Elementary Particles Elementary Particles   
Elementary Particles Elementary Particles
The term elementary particles signify the particles of structureless and those can The term elementary particles signify the particles of structureless and those can
not be constructed from other particles. not be constructed from other particles.
Present model of the constituents of matter is that they consist of fundamental Present model of the constituents of matter is that they consist of fundamental
point like, on a scale of 10 point like, on a scale of 10
-17 -17
  m, spin ½ fermions- the quarks with fractional   m, spin ½ fermions- the quarks with fractional
electric charge and the leptons carrying zero or integral electric charge. Hence electric charge and the leptons carrying zero or integral electric charge. Hence
there are two types of fundamental fermions, called quarks and leptons, which there are two types of fundamental fermions, called quarks and leptons, which
are structuresless and point like. are structuresless and point like.
One of the important modern ideas of forces is that forces between particles One of the important modern ideas of forces is that forces between particles
arise from the exchange of particles. arise from the exchange of particles.
Cl ssif atio of El me ta y a t c es Classification of Elementary Particles
   
The elementary particles are classified in terms of their mass, intrinsic spin, The elementary particles are classified in terms of their mass, intrinsic spin,
magnetic moment and interaction properties. magnetic moment and interaction properties.
The following table represents the list of The following table represents the list of such particles: such particles:
Elementary Particles Elementary Particles
Hadrons (Quarks) Hadrons (Quarks)
Baryon Baryon Photon Leptons Photon Leptons Mesons Mesons
Nucleon Hyperons Nucleon Hyperons
Photon Photon   
Photon Photon
The first member of elementary particles is gamma ray photons, which is an The first member of elementary particles is gamma ray photons, which is an
electromagnetic quantum. electromagnetic quantum.
• •   These particles take part These particles take part in electromagnetic interactions. in electromagnetic interactions.
• •   They have zero rest mass and zero spin. They have zero rest mass and zero spin.
• •   They are bosons. They are bosons.
   
2 2
Leptons Leptons   
Leptons Leptons
The second category of elementary particles is called lepton, which consists of The second category of elementary particles is called lepton, which consists of
light particles. light particles.
• •
   
They take part in electromagnetic and weak interactions and They take part in electromagnetic and weak interactions and
• •   They have half-odd integral spins. They have half-odd integral spins.
• •   They are fermions They are fermions
Types of leptons Types of leptons
There are two types of There are two types of leptons: leptons:
(a) (a)   Charged, and (b) Neutral. Charged, and (b) Neutral.
Charged leptons Charged leptons
The charged leptons are electron, The charged leptons are electron,  µ   µ  -meson or muon, and -meson or muon, and t  t  -lepton. These leptons -lepton. These leptons
occur in doublet that is positively and negatively charged. occur in doublet that is positively and negatively charged.
Neutral leptons Neutral leptons
The neutral leptons are known as neutrinos. They are neutral particles having The neutral leptons are known as neutrinos. They are neutral particles having
zero rest mass. zero rest mass.
There are three types of neutrinos associated with each type of lepton and There are three types of neutrinos associated with each type of lepton and
correspondingly called correspondingly called e e-neutrino and -neutrino and µ   µ  -neutrino -neutrino ? ?   t  t  -neutrino. -neutrino.
Electron Electron
Electrons are leptons, which are negatively charged stable particles. Their mass Electrons are leptons, which are negatively charged stable particles. Their mass
is about 5.48 x 10 is about 5.48 x 10
-4 -4
 amu.  amu.
Muon Muon
Muons are leptons, which are also negatively charged particles but heavier than Muons are leptons, which are also negatively charged particles but heavier than
electrons. Their mass is 207 times mass of electrons. They are characterized by electrons. Their mass is 207 times mass of electrons. They are characterized by
life of the order of 10 life of the order of 10
-6 -6
sec. sec.
Neutrinos Neutrinos
t  ton was first observed -lepton was first observed in accelerator experiments in 1974. in accelerator experiments in 1974.
Hadrons Hadrons
Hadrons Hadrons
These are the strongly interacting heavy particles. These are the strongly interacting heavy particles.
Types of Hadrons Types of Hadrons
They are classified into two types: Mesons and They are classified into two types: Mesons and Baryons. Baryons.
Mesons Mesons
These are particles heavier than electrons and lighter than nucleons. These are particles heavier than electrons and lighter than nucleons. Their mass Their mass
lies between 250 and 1000 times mass of lies between 250 and 1000 times mass of the electrons. the electrons.
• •
   
These particles have strong interaction with nuclear matter These particles have strong interaction with nuclear matter
• •    They are particles of nuclear field. They are particles of nuclear field.
   
3 3
• •    They have zero intrinsic spin, They have zero intrinsic spin,
• •    They are bosons. They are bosons.
Types of Mesons Types of Mesons
Mesons are divided into three groups: Mesons are divided into three groups: p p-Meson (pion), k-meson (kaon), and -Meson (pion), k-meson (kaon), and ? ?- -
meson. meson.
p  p  p p p  p  p  p  -Mesons -Mesons   
p  p  -Mesons are found to have three states of charge: -Mesons are found to have three states of charge:
(a) Positive, (a) Positive, p  p     
+ +
, , (b) (b) Negative, Negative, p  p     
- -
 and (c) Neutral,  and (c) Neutral, p  p     
0 0
. .
Positive Positive p  p  -meson has mass of 275 times mass of electrons and life of about 10 -meson has mass of 275 times mass of electrons and life of about 10
-2 -2
   
sec. sec.
Neutral Neutral p  p  -meson has mass of 264 times mass of the electron. -meson has mass of 264 times mass of the electron.
Neutral Neutral p  p     
0 0
  mesons are produced in the collision of protons having Kinetic   mesons are produced in the collision of protons having Kinetic
energy energy = = 150 MeV.  150 MeV. Similarly, in photoproduction of energetic gamma quanta, Similarly, in photoproduction of energetic gamma quanta, p  p     
+ +
- -mesons are produced. mesons are produced.
K-Mesons K-Mesons
K-Mesons are found to be in three charge states: K-Mesons are found to be in three charge states:
(a) Positive, (a) Positive, k  k   +  +, (b) Negative, , (b) Negative, k  k     
- -
, and (c) Neutral, , and (c) Neutral, k  k  0 0   
Positive k-meson has mass 966 times of the electronic mass. And that neutral Positive k-meson has mass 966 times of the electronic mass. And that neutral k  k  - -
mesons have 967 times electronic mass. mesons have 967 times electronic mass.
Baryons Baryons   
Baryons Baryons
These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons
are further grouped into two classes: are further grouped into two classes: (a) nucleon, and (b) hyperons. (a) nucleon, and (b) hyperons.
Nucleons are constituent particles of the nucleus of an atom. They are protons Nucleons are constituent particles of the nucleus of an atom. They are protons
and neutrons. Protons and neutrons have nearly equal mass. But protons are and neutrons. Protons and neutrons have nearly equal mass. But protons are
positively charged and neutrons are neutral. positively charged and neutrons are neutral.
Hyperons Hyperons   
Hyperons Hyperons
Hyperons are the particles heavier than nucleons. They are characterized by Hyperons are the particles heavier than nucleons. They are characterized by
their lifetime, which has the order of 10 their lifetime, which has the order of 10
-10 -10
  sec. The hyperons have strange   sec. The hyperons have strange
behavior that they decay faster than are behavior that they decay faster than are formed. formed.
Types of hyperons Types of hyperons
There are four types of hyperons: There are four types of hyperons:
? ?-hyperon, -hyperon, S S-hyperons, -hyperons, ? ?-hyperons and -hyperons and ? ?-hyperons. -hyperons.
? ?
-hyperons are neutral particles and so ar -hyperons are neutral particles and so are represented as e represented as
? ?
0 0
S S-hyperons exist in three charge states -hyperons exist in three charge states
   
4 4
(a) (a) S S
+ +
, (b) , (b) S S   
- -
, and , and S S   
0 0
, ,
? ?-hyperon in two charge states: -hyperon in two charge states:
(a) Positive (a) Positive ? ?
+ +
, and (b) Negative , and (b) Negative ? ?
- -
   
? ?-hyperon exits in only one charge state -hyperon exits in only one charge state ? ?
- -
. .
Resonances Resonances
In addition to particles listed above, a great number of strongly interacting short- In addition to particles listed above, a great number of strongly interacting short-
lived particles, called resonances, has been discovered. These particles are lived particles, called resonances, has been discovered. These particles are
resonance states of two or more resonance states of two or more elementary particles elementary particles. The lifetime of resonances . The lifetime of resonances
is only about 10 is only about 10
-23 -23
  to 10   to 10
-22 -22
  sec. Some of resonances are bosons and must be   sec. Some of resonances are bosons and must be
included in the class of included in the class of mesons. Others are fermions and mesons. Others are fermions and must be included in the must be included in the
class of hyperons. class of hyperons.
Antiparticles Antiparticles   
Antiparticles Antiparticles
Antiparticle of a particle is the particle having the same mass but of opposite Antiparticle of a particle is the particle having the same mass but of opposite
charge. When the particle and its antiparticle come in contact they annihilate charge. When the particle and its antiparticle come in contact they annihilate
each other with the emission of photons. All the particles have their antiparticle. each other with the emission of photons. All the particles have their antiparticle.
Positron is the first discovered antiparticle of electron. The antiproton is Positron is the first discovered antiparticle of electron. The antiproton is
discovered by Segre, Chamberlain and other in the collision of high energy discovered by Segre, Chamberlain and other in the collision of high energy
protons. protons.
The antiparticle of neutron, the antineutron, was discovered in 1956 by Cork, The antiparticle of neutron, the antineutron, was discovered in 1956 by Cork,
Lamberton and Wengel. Lamberton and Wengel.
Neutrino and antineutrino are distinguished by their spins. Neutrino spins Neutrino and antineutrino are distinguished by their spins. Neutrino spins
counterclockwise while antineutrino clockwise. counterclockwise while antineutrino clockwise.
Quarks Quarks   
Quarks Quarks
Hadrons are built up from a limited number of fundamental units, which have Hadrons are built up from a limited number of fundamental units, which have
acquired the name quarks. These fundamental units have unusual properties that acquired the name quarks. These fundamental units have unusual properties that
they carry fractional electric charge. they carry fractional electric charge.
Types of quarks Types of quarks
The original theory postulated three quarks, which are labeled The original theory postulated three quarks, which are labeled u u-, -, d  d  - and - and s s, ,
which stand for which stand for up up, , down down  and   and strange strange. We refer to these labels as . We refer to these labels as  flavors  flavors    of of
quarks. quarks.
• •    The quarks have a spin quantum number of The quarks have a spin quantum number of ½ and ½ and
• •    They have baryon number of 1/3. They have baryon number of 1/3.
• •
   
Hence, quarks are fermions. Hence, quarks are fermions.
Charge, strangeness and baryon number for these quarks Charge, strangeness and baryon number for these quarks are as follows: are as follows:
Page 5


   
Elementary Particles Elementary Particles
Elementary Particles Elementary Particles   
Elementary Particles Elementary Particles
The term elementary particles signify the particles of structureless and those can The term elementary particles signify the particles of structureless and those can
not be constructed from other particles. not be constructed from other particles.
Present model of the constituents of matter is that they consist of fundamental Present model of the constituents of matter is that they consist of fundamental
point like, on a scale of 10 point like, on a scale of 10
-17 -17
  m, spin ½ fermions- the quarks with fractional   m, spin ½ fermions- the quarks with fractional
electric charge and the leptons carrying zero or integral electric charge. Hence electric charge and the leptons carrying zero or integral electric charge. Hence
there are two types of fundamental fermions, called quarks and leptons, which there are two types of fundamental fermions, called quarks and leptons, which
are structuresless and point like. are structuresless and point like.
One of the important modern ideas of forces is that forces between particles One of the important modern ideas of forces is that forces between particles
arise from the exchange of particles. arise from the exchange of particles.
Cl ssif atio of El me ta y a t c es Classification of Elementary Particles
   
The elementary particles are classified in terms of their mass, intrinsic spin, The elementary particles are classified in terms of their mass, intrinsic spin,
magnetic moment and interaction properties. magnetic moment and interaction properties.
The following table represents the list of The following table represents the list of such particles: such particles:
Elementary Particles Elementary Particles
Hadrons (Quarks) Hadrons (Quarks)
Baryon Baryon Photon Leptons Photon Leptons Mesons Mesons
Nucleon Hyperons Nucleon Hyperons
Photon Photon   
Photon Photon
The first member of elementary particles is gamma ray photons, which is an The first member of elementary particles is gamma ray photons, which is an
electromagnetic quantum. electromagnetic quantum.
• •   These particles take part These particles take part in electromagnetic interactions. in electromagnetic interactions.
• •   They have zero rest mass and zero spin. They have zero rest mass and zero spin.
• •   They are bosons. They are bosons.
   
2 2
Leptons Leptons   
Leptons Leptons
The second category of elementary particles is called lepton, which consists of The second category of elementary particles is called lepton, which consists of
light particles. light particles.
• •
   
They take part in electromagnetic and weak interactions and They take part in electromagnetic and weak interactions and
• •   They have half-odd integral spins. They have half-odd integral spins.
• •   They are fermions They are fermions
Types of leptons Types of leptons
There are two types of There are two types of leptons: leptons:
(a) (a)   Charged, and (b) Neutral. Charged, and (b) Neutral.
Charged leptons Charged leptons
The charged leptons are electron, The charged leptons are electron,  µ   µ  -meson or muon, and -meson or muon, and t  t  -lepton. These leptons -lepton. These leptons
occur in doublet that is positively and negatively charged. occur in doublet that is positively and negatively charged.
Neutral leptons Neutral leptons
The neutral leptons are known as neutrinos. They are neutral particles having The neutral leptons are known as neutrinos. They are neutral particles having
zero rest mass. zero rest mass.
There are three types of neutrinos associated with each type of lepton and There are three types of neutrinos associated with each type of lepton and
correspondingly called correspondingly called e e-neutrino and -neutrino and µ   µ  -neutrino -neutrino ? ?   t  t  -neutrino. -neutrino.
Electron Electron
Electrons are leptons, which are negatively charged stable particles. Their mass Electrons are leptons, which are negatively charged stable particles. Their mass
is about 5.48 x 10 is about 5.48 x 10
-4 -4
 amu.  amu.
Muon Muon
Muons are leptons, which are also negatively charged particles but heavier than Muons are leptons, which are also negatively charged particles but heavier than
electrons. Their mass is 207 times mass of electrons. They are characterized by electrons. Their mass is 207 times mass of electrons. They are characterized by
life of the order of 10 life of the order of 10
-6 -6
sec. sec.
Neutrinos Neutrinos
t  ton was first observed -lepton was first observed in accelerator experiments in 1974. in accelerator experiments in 1974.
Hadrons Hadrons
Hadrons Hadrons
These are the strongly interacting heavy particles. These are the strongly interacting heavy particles.
Types of Hadrons Types of Hadrons
They are classified into two types: Mesons and They are classified into two types: Mesons and Baryons. Baryons.
Mesons Mesons
These are particles heavier than electrons and lighter than nucleons. These are particles heavier than electrons and lighter than nucleons. Their mass Their mass
lies between 250 and 1000 times mass of lies between 250 and 1000 times mass of the electrons. the electrons.
• •
   
These particles have strong interaction with nuclear matter These particles have strong interaction with nuclear matter
• •    They are particles of nuclear field. They are particles of nuclear field.
   
3 3
• •    They have zero intrinsic spin, They have zero intrinsic spin,
• •    They are bosons. They are bosons.
Types of Mesons Types of Mesons
Mesons are divided into three groups: Mesons are divided into three groups: p p-Meson (pion), k-meson (kaon), and -Meson (pion), k-meson (kaon), and ? ?- -
meson. meson.
p  p  p p p  p  p  p  -Mesons -Mesons   
p  p  -Mesons are found to have three states of charge: -Mesons are found to have three states of charge:
(a) Positive, (a) Positive, p  p     
+ +
, , (b) (b) Negative, Negative, p  p     
- -
 and (c) Neutral,  and (c) Neutral, p  p     
0 0
. .
Positive Positive p  p  -meson has mass of 275 times mass of electrons and life of about 10 -meson has mass of 275 times mass of electrons and life of about 10
-2 -2
   
sec. sec.
Neutral Neutral p  p  -meson has mass of 264 times mass of the electron. -meson has mass of 264 times mass of the electron.
Neutral Neutral p  p     
0 0
  mesons are produced in the collision of protons having Kinetic   mesons are produced in the collision of protons having Kinetic
energy energy = = 150 MeV.  150 MeV. Similarly, in photoproduction of energetic gamma quanta, Similarly, in photoproduction of energetic gamma quanta, p  p     
+ +
- -mesons are produced. mesons are produced.
K-Mesons K-Mesons
K-Mesons are found to be in three charge states: K-Mesons are found to be in three charge states:
(a) Positive, (a) Positive, k  k   +  +, (b) Negative, , (b) Negative, k  k     
- -
, and (c) Neutral, , and (c) Neutral, k  k  0 0   
Positive k-meson has mass 966 times of the electronic mass. And that neutral Positive k-meson has mass 966 times of the electronic mass. And that neutral k  k  - -
mesons have 967 times electronic mass. mesons have 967 times electronic mass.
Baryons Baryons   
Baryons Baryons
These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons These are heavy particles. Their intrinsic spin is odd-half integer spin. Baryons
are further grouped into two classes: are further grouped into two classes: (a) nucleon, and (b) hyperons. (a) nucleon, and (b) hyperons.
Nucleons are constituent particles of the nucleus of an atom. They are protons Nucleons are constituent particles of the nucleus of an atom. They are protons
and neutrons. Protons and neutrons have nearly equal mass. But protons are and neutrons. Protons and neutrons have nearly equal mass. But protons are
positively charged and neutrons are neutral. positively charged and neutrons are neutral.
Hyperons Hyperons   
Hyperons Hyperons
Hyperons are the particles heavier than nucleons. They are characterized by Hyperons are the particles heavier than nucleons. They are characterized by
their lifetime, which has the order of 10 their lifetime, which has the order of 10
-10 -10
  sec. The hyperons have strange   sec. The hyperons have strange
behavior that they decay faster than are behavior that they decay faster than are formed. formed.
Types of hyperons Types of hyperons
There are four types of hyperons: There are four types of hyperons:
? ?-hyperon, -hyperon, S S-hyperons, -hyperons, ? ?-hyperons and -hyperons and ? ?-hyperons. -hyperons.
? ?
-hyperons are neutral particles and so ar -hyperons are neutral particles and so are represented as e represented as
? ?
0 0
S S-hyperons exist in three charge states -hyperons exist in three charge states
   
4 4
(a) (a) S S
+ +
, (b) , (b) S S   
- -
, and , and S S   
0 0
, ,
? ?-hyperon in two charge states: -hyperon in two charge states:
(a) Positive (a) Positive ? ?
+ +
, and (b) Negative , and (b) Negative ? ?
- -
   
? ?-hyperon exits in only one charge state -hyperon exits in only one charge state ? ?
- -
. .
Resonances Resonances
In addition to particles listed above, a great number of strongly interacting short- In addition to particles listed above, a great number of strongly interacting short-
lived particles, called resonances, has been discovered. These particles are lived particles, called resonances, has been discovered. These particles are
resonance states of two or more resonance states of two or more elementary particles elementary particles. The lifetime of resonances . The lifetime of resonances
is only about 10 is only about 10
-23 -23
  to 10   to 10
-22 -22
  sec. Some of resonances are bosons and must be   sec. Some of resonances are bosons and must be
included in the class of included in the class of mesons. Others are fermions and mesons. Others are fermions and must be included in the must be included in the
class of hyperons. class of hyperons.
Antiparticles Antiparticles   
Antiparticles Antiparticles
Antiparticle of a particle is the particle having the same mass but of opposite Antiparticle of a particle is the particle having the same mass but of opposite
charge. When the particle and its antiparticle come in contact they annihilate charge. When the particle and its antiparticle come in contact they annihilate
each other with the emission of photons. All the particles have their antiparticle. each other with the emission of photons. All the particles have their antiparticle.
Positron is the first discovered antiparticle of electron. The antiproton is Positron is the first discovered antiparticle of electron. The antiproton is
discovered by Segre, Chamberlain and other in the collision of high energy discovered by Segre, Chamberlain and other in the collision of high energy
protons. protons.
The antiparticle of neutron, the antineutron, was discovered in 1956 by Cork, The antiparticle of neutron, the antineutron, was discovered in 1956 by Cork,
Lamberton and Wengel. Lamberton and Wengel.
Neutrino and antineutrino are distinguished by their spins. Neutrino spins Neutrino and antineutrino are distinguished by their spins. Neutrino spins
counterclockwise while antineutrino clockwise. counterclockwise while antineutrino clockwise.
Quarks Quarks   
Quarks Quarks
Hadrons are built up from a limited number of fundamental units, which have Hadrons are built up from a limited number of fundamental units, which have
acquired the name quarks. These fundamental units have unusual properties that acquired the name quarks. These fundamental units have unusual properties that
they carry fractional electric charge. they carry fractional electric charge.
Types of quarks Types of quarks
The original theory postulated three quarks, which are labeled The original theory postulated three quarks, which are labeled u u-, -, d  d  - and - and s s, ,
which stand for which stand for up up, , down down  and   and strange strange. We refer to these labels as . We refer to these labels as  flavors  flavors    of of
quarks. quarks.
• •    The quarks have a spin quantum number of The quarks have a spin quantum number of ½ and ½ and
• •    They have baryon number of 1/3. They have baryon number of 1/3.
• •
   
Hence, quarks are fermions. Hence, quarks are fermions.
Charge, strangeness and baryon number for these quarks Charge, strangeness and baryon number for these quarks are as follows: are as follows:
   
5 5
Quark Quark Electric Electric Charge Charge Strangeness Strangeness Baryon Baryon Number Number
u u-quark -quark +2/3 0 +2/3 0 1/3 1/3
d  d  -quark -quark
- -1/3 1/3
0 1/3 0 1/3
s s-quark -quark
- -1/3 1/3 - -1 1
1/3 1/3
Each quark has an anti-quark associated with it ( Each quark has an anti-quark associated with it ( s s d  d  u u , , , , ). The magnitude of ). The magnitude of
charge and baryon number for the anti-quarks has the same magnitude as those charge and baryon number for the anti-quarks has the same magnitude as those
the quarks, but the sign is the quarks, but the sign is reversed. reversed.
Composition of hadrons according to the quark model Composition of hadrons according to the quark model   
Composition of hadrons according to the quark model Composition of hadrons according to the quark model
A baryon is made up of three quarks. For example, the proton is made up of two A baryon is made up of three quarks. For example, the proton is made up of two
u u-quarks and a -quarks and a d  d  -quark (uud) so that, -quark (uud) so that,
Hadrons Hadrons Total Total charge charge Baryon Baryon number number Strangene Strangene
ss ss
Quark Quark
combination combination
proton proton
2/3 + 2/3 + ( 2/3 + 2/3 + (- -1/3) = 1/3) =
1 1
1/3 + 1/3 + 1/3 1/3 + 1/3 + 1/3
= 1 = 1
0 + 0 + 0 0 + 0 + 0
= 0 = 0
uud uud Baryo Baryo
n n
neutron neutron
2/3 + ( 2/3 + (- -1/3) + ( 1/3) + (- -1/3) 1/3)
= 0 = 0
1/3 + 1/3 + 1/3 1/3 + 1/3 + 1/3
= 1 = 1
0 + 0 + 0 0 + 0 + 0
= 0 = 0
udd udd
A meson is made up of a quark and an anti-quark. For example, the A meson is made up of a quark and an anti-quark. For example, the p  p 
+ +
-meson is -meson is
the combination of a the combination of a u u-quark and a -quark and a d  d  -antiquark (u -antiquark (u?    ?    d), d), p  p 
- - - -
-meson is the -meson is the
combination of a combination of a u u-antiquark and a -antiquark and a d  d  -quark (ud). K -quark (ud). K
+ +
has quark combination (u has quark combination (u?    ?    s) s)
and K and K
- -
 has (  has (?    ?    us). us).
Coloured Quarks Coloured Quarks   
It is believed that It is believed that ?  ? 
- -
-hyperon is composed of three identical -hyperon is composed of three identical s s-quarks ( -quarks (sss sss). So, ). So,
there is a problem with this quark model, because it violates the Pauli Exclusion there is a problem with this quark model, because it violates the Pauli Exclusion
Principle that prohibits two or more fermions from occupying identical quantum Principle that prohibits two or more fermions from occupying identical quantum
states. Similarly, the proton, neutron, and others with two identical quarks would states. Similarly, the proton, neutron, and others with two identical quarks would
violate this principle also. To resolve this difficulty, a new property is assigned to violate this principle also. To resolve this difficulty, a new property is assigned to
the quarks, which can be regarded as new quantum number. The new quantum the quarks, which can be regarded as new quantum number. The new quantum
number is called number is called colour  colour  . There are three colours labeled Red (R), Blue (B), and . There are three colours labeled Red (R), Blue (B), and
Green (G), which distinguish three identical quarks. Green (G), which distinguish three identical quarks.