PARTICLE PHYSICS CLASS 11 NOtes
INTRODUCTION
Elementary particles are the fundamental constituents of all the matter
in the universe. The branch of physics concerned with the property,
interaction, and structure of elementary particles is called particle
physics.
· Elementary particles
The particles which are structureless, indivisible, and not regarded as
made up of some other particles are called elementary particles. Hundreds
of elementary particles are discovered so far. These particles are
fundamental in the sense that these particles can not be explained as the
system of other particles.
· Particles and antiparticles
The antiparticle of a particle has the same mass, spin and lifetime if
unstable, but its charge(if any) has the opposite nature. Every particle has
its own antiparticle.
The anti-particle of the electron is a positron that has the same mass as
of electron but opposite charge.
The antiparticle of the proton is an antiproton that has the same mass as
of proton but the opposite charge.
The combination of particles gives matter and the combination of
antiparticles gives antimatter.
•The antiparticle of a particle is represented by putting the bar over the
symbol for the particle. The symbol of the proton is ‘p’ so its antiparticle
is (p compliment).
· Annihilation
The process in which, when a particle
interacts with its antiparticle, they destroyed converting into energy is
called annihilation.
When an electron and 1a positron come very close to each
other, they annihilate each other by combining together and two gamma rays
photons (energy) are produced.
-1e0 +
+1e0 = y + y
electron positron photon
· Pair production
When an energetic y- ray photon falls on a heavy substance, it is absorbed by some nucleus of
the substance, and its energy gives rise to the production of an electron
and a positron. This phenomenon in which energy is converted into mass is
called pair-production. It is represented by the following equation:
Y = -1e0 + +1e0
· Classification of elementary particles
Elementary particles or fundamental particles
|
Leptons |
Quarks |
Mediator particles |
|
electron (e-) |
Up (u) |
Gluons |
|
electron neutrino (ve) |
Down (d) |
Photons |
|
muon ( µ-) |
Charm (c) |
Intermediate boson |
|
muon neutrino (vµ) |
Strange (s) |
graviton |
|
taun |
Top (t) |
|
|
taun neutrino |
Bottom (b) |
|
· Leptons
Leptons are the light weight elementary particles. They do not have strong
interactions. They are fermions. they have spin 1/2. there are six leptons.
Each of six particles has six distinct anti particles.
· Quarks
A quark is a type of elementary particle and a fundamental constituent of
matter. Quarks combine to form composite particles called hadrons, the most
stable of which are protons and neutrons, the components of atomic nuclei.
They are strongly interacting particles. No isolated existence of quark is
discovered so far. There are six types of quarks and each quark has its own
anti quark.
|
Quarks |
Symbol |
charge |
Baryon number |
Strangeness |
|
Up |
u |
+2/3 |
1/3 |
0 |
|
Down |
d |
-1/3 |
1/3 |
0 |
|
Charm |
c |
+2/3 |
1/3 |
0 |
|
Strange |
s |
-1/3 |
1/3 |
-1 |
|
Top |
t |
+2/3 |
1/3 |
0 |
|
Bottom |
b |
-1/3 |
1/3 |
0 |
· Hadrons
Heavy particles that interact by the strong interaction are called hadrons.
This general classification includes mesons and baryons.
Hadrons
Barions Mesons
Nucleons hyperons (pions,
kaons,etc)
(protons,neutrons) (lambda,sigma,etc.)
· Mesons
Particles have a mass intermediate between lepton and baryon. They have
spin-zero or integral spin and so-called boson. It is a combination of quark
and anti quark.
· Color and Flavor of quarks
A serious problem with the quark model was that the presence of two or
three quarks of the same kind in a particular particle (for example, two up
quarks in a proton and two identical down quarks in neutron). This violates
the Pauli exclusion principle but quarks are fermions with spin ½ so they
should follow the Pauli exclusion principle. This problem is resolved by
assigning a new property to quarks and anti quarks which is called color.
There are three colors which are red, blue, and green. The anti-quark colors
are antired antiblue and anti-green.
The distinction between the six quarks was referred to as flavors. There is
six flavors of quarks in nature. Flavors mean varieties.
Baryon – three quarks and one of each color(colorless)
Meson- quark + antiquark and color +anticolor(colorless)
·
Universe
Red Shift and expanding of the
universe
According to the Doppler effect, there is an apparent change in the
wavelength of waves emitted by a source when it is in motion with respect to
an observer. The apparent wavelength observed by an observer is increased if
the source is moving away from the observer and is decreased if the source
is moving towards the observer.
The application of the Doppler Effect to the light emitted by a star in a
galaxy confirms whether stars are moving towards the earth. If stars are
moving towards the earth or away from the earth, the wavelength of the light
emitted by it will decrease gradually and shift towards the violet end of
the visible spectrum. VIBGYOR this shift in wavelength toward the violet end
of the visible spectrum is called blue shift.
Contrary to this if the star is moving away from us, the wavelength of the
light emitted by it will increase and shift toward the red end of the
visible spectrum VIBGYOR. This shift in wavelength toward the red end is
called the red shift.
In most cases, stars or galaxies are found to be moving away from the
earth. Hence all the galaxies are running from each other and therefore
the universe is expanding.
· Hubble’s law
Analysis of the red shift from many distant galaxies led Edwin Hubble to a
remarkable conclusion called Hubble law. It states that the speed of
recession of a galaxy is proportional to its distance from us.
If v is the speed of recession of galaxy and r is its distance from earth.
Then
vα r
or v= Hor, where Ho is Hubble’s constant. Its value is 2.3x10-18s-1
· The Big Bang
Hubble’s law suggests that at some time in the past, all the matter
in the universe was far more concentrated today. It was then blown apart on
an immense explosive called the big bang, giving all observable matter more
or less the velocities that we observe today.
According to Hubble law, the matter at a distance away from us is traveling
with speed v= Ho r
The time needed to travel a distance r is given by,
t=r/v
∴t=r/ Ho
t=1/ Ho =4.3× 1017s=1.4× 1010years
By this hypothesis, the big bang occurred about 14 billion years ago. It
assumes that all speeds are constant after the big bang; that is it neglects
any changes in the expansion rate due to gravitational attraction or other
effects.
If v be the speed of our galaxy relative to the center of the sphere, then
by Hubble’s law,
v= HoR (iv)
From equation (ii), (iii) and (iv) , we get
½ m(H0R)2 = Gm/R ( 4/3 πR3рϲ)
[рϲ = 3 H0 2/8πG]
Putting value of HO=2.3x 10-18 s-1 and G=6.67x 10-11 Kgm2s-2 we get
ρc=6.3x10-27kg/m3
· Dark energy and dark matter
•Dark matter is the non-luminous material distributed throughout the
universe that cannot be directly detected by observing any form of
electromagnetic radiation but whose existence is suggested by gravitational
effects on visible matter. According to present observations of a structure
larger than the galaxy, big bang cosmology, dark matter, and dark energy
account for the vast majority of the mass in the observable universe.
•The galaxies near the Milky Way appear to be rotating faster than the
rotation rate expected from the amount of visible matter that appears to be
in these galaxies. Many astronomers believe that 96% of the matter in a
typical galaxy is invisible. Some astronomers argue that the cluster
galaxies are bound together from billions of years by gravity due to the
presence of enough mass which includes up to 96 % dark matter and energy
(72% dark energy, 24% dark matter).
· Gravitational wave
Gravitational
waves are 'ripples' in space-time caused by some of the most violent and
energetic processes in the Universe. Albert Einstein predicted the existence
of gravitational waves in 1916 in his general theory of relativity.
Einstein's mathematics showed that massive accelerating objects (such as
neutron stars or black holes orbiting each other) would disrupt space-time
in such a way that 'waves' of undulating space-time would propagate in all
directions away from the source. These cosmic ripples would travel at the
speed of light, carrying with them information about their origins, as well
as clues to the nature of gravity itself.
First detection of a gravitational wave on September 14, 2015
