This document is a project report submitted by Priyanka Verma and Smriti Singh for their Bachelor of Science degree in physics. It discusses elementary particles, including their characteristics, classification, conservation laws, and examples like electrons, positrons, protons, neutrons, pions, and kaons. The report includes certificates of completion from their college principal and physics professors.

1. Shri Agrasen Kanya Autonomous
P.G. College, Varanasi
External Supervisor Internal Supervisor
Dr. Shubha R. Saxena (HOD)
Dr. Sunil Mishra
Shri A. K. A. P. G. College
Varanasi
Submitted by
Priyanka Verma
Smriti Singh
B. Sc. (Final Year)
A Project on: Elementary particles
Subject:- Physics
Session: 2015-16
Bachelor of Science
In
Physics

2. Sri Agrasen Kanya Autonomous P.G. College
Varanasi – 221001
CERTIFICATE
This is to certify that the Project Work
entitled Elementary Particles in Atom.
A Project report has been undertaken
in much supervision and guidance, the
result presented in the project report is
based on her own independent effort
that had been checked and verify by me. I
am fully satisfied with the work which is
being presented by Smriti Singh &
Priyanka Verma.
Forwarded by Supervised by
Dr. Kumkum Malviya Dr. Shubha R. Saxena (HOD)
Principal Dr. Sunil Mishra
Sri A.K.P.G. College Department Of Physics
Bulanala, Varanasi Sri A.K.P.G. College
Bulanala, Varanasi

3. ACKNOWLEDGEMENT
I am thankful to our Principal Dr.
Kumkum Malviya, I am deeply indebted
by our Mam Dr. Shubha R Saxena Head,
of Department of Physics, Shri A. K. A.
P.G. College, Varanasi for inspiring and
providing important books S. N. Ghosal,
S.Chand & David Griffith for this work.
I am thankful to respected teacher
Dr. Sunil Mishra Department of Physics,
Shri A. K. A. P.G. P.G. College, and
Varanasi for helping me lots by; giving
suggestion and guidance.
I am heartily thankful to all our
teachers of the department whose great
blessing and love made it possible for
me to go and succeeded in my work.
Priyanka Verma& Smriti Singh
B.Sc. (Physics)
Final year

4. CONTENTS
INTRODUCTION
ELEMENTARY PARTICLES
CHARACTERISTICS
PARTICLES AND ANTIPARTICLES
CLASSIFICATION
CONSERVATION LAWS

5. INTRODUCTION
Matter in this universe is supposed to
be made of microscopic elementary
constituents these particles are known
as elementary particles. A few of
them, such as Proton, Electron, are
stable but most of them decay soon
after their production

6. Elementaryor fundamentalparticles
An elementary particle is
one which is not a composite
of others, i.e., whose internal
structure cannot be describe
as a combination of other
particles.
In early 30’s people knew
about only four elementary
particles-the electron, the
proton, the neutron and the
photon. This number had
grown to 14 by 1947 and to
32 by 1957.

8. Characteristicproperties of elementary
particles
Mass:-An elementary
particles has always the same
rest mass. The magnitude of
the rest mass serves as the
principal label to identify the
particle uniquely.
Charge :-All elementary
particles have charge +e, -e or
zero. This charge or conserved
in any collision process. It may
be seen from the following
neutron-proton(n-p) collision:
n + p -> p + p + π¯
n + p -> n + n + π⁺
n + p -> n + p + k⁻ + k⁺

9. Life time :-All elementary
particles, except photon,
electron, proton and neutrinos,
are unstable and decay into
other elementary particles of
smaller mass.
Spin :- the particles of half
integral, i.e., spins,, etc.
obeying Fermi-Dirac statistics,
are called Fermions. The
particles of spins are
electrons, positrons, protons,
neutrons, neutrinos,
antineutrinos, µ-mesons and
many hyperons. Particles having
zero or integral spins, i.e., 0, 1,
2 etc. are bosons because they
obey Bose-Einstein statistic.

10. Interactions
Gravitational interactions
It is the weakest interaction which is
attractive and universal.
Weak interactions
These interaction cause the light
particles to interact with one another
and with heavier particles.
Electromagnetic interactions
It is similar to the gravitational
interactions but depends upon the
nature of charges on the particles.
Strong interactions
It is the dominant interaction in high-
energy particles physics. These are
also called nuclear interaction.
The relative magnitudes of
gravitational, weak, electromagnetic
and strong interactions are in the
ratio:
10-39: 10-13: 10-3: 1

12. PARTICLES AND
ANTI-PARTICLES
Dirac predicted theoretically the existence of
antiparticles for the electron. He actually
postulated that every particle has
antiparticles. The antiparticles of a given
particles has exactly the same mass, spin, and
life time (if unstable) but an opposite charge
(if any).
Electron and positron
The first antiparticles known was positron
which was discovered by Anderson in 1932. It
is a positively charged electron, i.e., it has the
same mass and the same spin as an electron but
opposite charge. When an electron and a
positron come in contact with each other.
e+ + e- = 2ϒ
Proton and antiproton
The antiparticles of proton are called the
antiproton. It has the same mass as a proton,
but an opposite charge and the same spin as a
proton but an opposite magnetic moment. Thus
it is a negative proton and is denoted by p- . It
was established in1955 by Segre, Chamberlain
and their collaborators.

13. Neutron and antineutron
It is much harder to detect an antineutron
because it has no charge. Both neutron
and antineutron have zero charge and the
same mass but antineutron is supposed to
have an internal charge distribution to
that of neutron.
Neutrino and antineutrino
The antiparticles of neutrino v are
antineutrino. The neutrino spins counter
clockwise when viewed from behind from
behind, while antineutrino spins clockwise.

14. Classificationof elementaryparticles
On the basis of the characteristic
properties such as mass, spin, intrinsic
angular momentum and the nature of
reactions they can undergo, the
elementary particles are usually
classified into following groups.

15. Photons
Photon is a quantum of electromagnetic radiation. It
is a stable particle with zero charge and zero rest
mass. It is a bosom because its spin is unity. It has
energy given by Planck’s equation E=hv where v is the
frequency of radiation. It has an equivalent mass
given by Einstein equation E=mc2. therefore,
Leptons
These are light weight elementary particles. They
have a spin equal to and are, therefore, fermions.
They are characterized by their Spin-momentum
.The leptons are
stable except muons. They interact weakly with
other particles and occur as particles and
antiparticles.
The members of lepton class are electron and
positron (e- , e+), muons (µ- , µ+), electron-neutrinos
(ve, e) and muon-neutrinos (vµ, µ).
Electron and positron
Electron is stable atomic particles of mass 9.1x10-31
kg and negative charge of 1.6x10-19 coulomb. It has
spin quantum number s= and so its angular momentum
has magnitude . Therefore, it is a fermion.
Positron is the antiparticle of electron. It is
identical with electron in all respects except that it
is positively charged. When electron and positron
come in contact, they annihilate each other
producing two ϒ-photons:
e+ + e- = ϒ + ϒ

16. Muons (or µ-Mesons)
Mu-mesons, called muons, were discovered by
Anderson in 1936. µ-mesons exist as both negative
and positive and are denoted by µ+ and µ-
respectively. They are created as π-meson decay in
cosmic radiations.
µ+ and µ- mesons have the same spin of and
resemble with positron and electron respectively in
all respects except the following:
Muons are heavier than electron or positron. They
have the same rest mass of 207 me is the mass of
electron.
Both µ+ and µ- mesons are unstable ( unlike electron
and positron) having an average life of 2.2x10-6 sec.
they decay spontaneously into an electron or
positron, a µ-neutrino and an ordinary neutrino
according to the following scheme:
µ+ -> e+ + µ + v
µ- -> e- + vµ +
Energy of 105 MeV is released in the decay.
Neutrinos and Antineutrinos:
These particles have negligible rest mass and no
charge. They have a spin value of and a spin
angular momentum .
Neutrinos are of two kinds. Those associated
with electrons are called simply neutrinos (v) or
electron neutrinos (ve) while those associated with
muons are called µ-neutrinos (vµ). Both of these
neutrinos have their antiparticles denoted by (or e)
and µ respectively. They participate in weal
interaction with matter and hence their detection
causes difficulty. In 1956, however, a nuclear
reaction induced by neutrinos was actually observed.

17. Mesons
Mesons are the agent of interaction between particles inside the
nucleus. Their existence was predicted by Yukawa in his meson theory of
nuclear forces.
Mesons are middle weight particles having masses intermediate between
the electrons and protons. They are all bosons having zero spin. They
possess zero intrinsic (spin) angular momentum and are unstable.
Variety of mesons is now known. They include:
Π π -mesons or pions
π-mesons were discovered in 1947 in the cosmic rays. They can exist in
three states: π +, π- and π0. The π+ and π- are antiparticles of each
other while π0 (neutral pi-meson) has no charge and it is its own anti
particle.
π + and π- mesons have a rest mass of 273 me (me being rest mass of
electron) while the rest mass of π+ meson is slightly less, equal to 264
me.
Pions interact strongly with nucleus
They are produced by collisions of high energy (kinetic energy 140 MeV)
protons with nucleons (proton or neutron) according to the following:
p + p = p + n + π+
p + n = p + p + π-
p + p = p + p + π0
They are also produced by annihilation of proton-antiproton and neutron-
antineutron:
p + p- = π+ + π- + π0
n + n = π+ + π- + π0
The π-mesons are unstable particles. The average life time of charged
π-mesons (π0 and π-) is of the order of 10-8 sec while that of neutral π-
mesons (π0) is still shorter (=9x10-17sec). Consequently, only a fraction of
cosmic ray π-mesons can reach and they decay in flight by weak
interaction into corresponding muons and µ-neutrinos:
Π+ -> µ+ + µ
π- -> µ- + µ
µ+ and µ- further decay into e+ and e- respectively.
The neutral π-meson (π0) decays by an electromagnetic interaction into
two high energy ϒ-photons:
π -> ϒ + ϒ

18. K-Mesons (or Kaons)
K-Mesons is a heavier class of
mesons. They exist as K+ and its
antiparticles k-1 and also as k0 and its
antiparticles 0.
The charged K-mesons (K+ and K-)
have rest masses of 966me, spin zero
and mean lives 1.2x10-8 sec. they
commonly decay giving rise to two or
three less massive particles:
K+ -> π+ + π+ + π-
K± -> π± + πo
K+ ->µ+ + Vµ
K+ ->π+ + πo + πo
The K0 mesons are produced through
strong interaction of high energy
pions and protons:
π- + p+ -> ᴧ0 + Ko
Where 0 is lambda particle.
η-Mesons: The central eta meson (ɳ+)
was discovered in1961. It has a rest
mass of 1073 me and a zero spin value
(boson). Its average half life is 7x10-
19 sec. in which it decays
electromagnetically in two photons.

19. Baryons
There are heavy weight elementary
particles, having their rest mass equal to
or greater than that of nucleon (Proton
and neutrons), but less than that of
deuteron. They have spin values of and
hence are fermions. They are strongly
interacting and posses intrinsic angular
momentum Except protons, all baryons
are unstable.
Baryons have been grouped into two
subclasses:
Nucleons
These are nuclear particles and include
proton (p), neutron (n) and their anti
particles, anti proton and anti neutron
. Proton has a mass 1836 me while neutron’s
mass Is 1839 me. They all have a spin of
and are fermions.
Hyperons
The baryons possessing the rest mass
greater than that of nucleons are called
hyperons. They are unstable and have an
average life time of the order of 10-10 sec.
Their decay time is very much greater
than the time of their formation (10-3 sec).
Therefore, these particles, along with the
K-mesons are called strange particles.

20. There are four types of hyperons
Lambda hyperons (ᴧ0):- There are two
lambda hyperons, which have zero
charge and 2181 me, rest mass. They
are represented by ᴧ0 and - one is
anti particles of the other.
Sigma Hyperons: - There are six particles
Σ+, ∑-, ∑0 and their anti particlesΣ+,Σ- ,Σo,
they have respectively positive, negative
and zero charges. Σ+ is the lightest of all
three particles having rest mass 2328
me.
Xi Hyperons: - There are four Xi-hyperons
each with a ret mass of 2580 me. They
are Ξ- Ξ(with negative charge) and their
anti particles.
Omega Hyperons: - - (with negative
charge) and its anti particles.
The spin of all hyperons is except that
of hyperons which have a spin of.

21. Conservation laws governing elementary
particles
The production and decay of
elementary particles is governed by
certain conservation laws. The
applications of these laws have led to
the discovery of new fundamental
particles. The discovery of neutrino in -
decay is such an example. In fact, by
assuming the validity of these laws,
many of the fundamental particles
were first predicted theoretically and
then discovered experimentally. These
conservation laws are essential
features of all interactions and are
listed below:
 Conservation of electric charge
 Conservation of mass energy
 Conservation of linear momentum
 Conservation of angular momentum
(spin)

22. Law of conservationof Lepton-Number
According to this law, in any
process the total lepton number
is always conserved. It includes
the conservation of electron-
lepton number (L) and
conservation of muon-lepton
number (M).
L = +1 for electron and e-neutrino
(e- and ve)
L = -1 for anti leptons (e+ and ve)
L = 0 for all other particles.
SimilarlY, muon-lepton number.
M = +1 for µ meson and µ neutrino
M = -1 for their antiparticles
M = 0 for all other particles.

23. Law of conservation of baryons number
According to this law, in any process,
the total baryon number is always
conserved. Conventionally, the baryon
number
B = +1 for baryons
B = -1 for anti baryons
B = 0 for all other particles
As an example, consider the decay of
neutron
N0 -> p+ + e- + e
For it B = 1 -> 0 + 0