Elementary Particles Presentation by Smriti and Priyanka

8/18/2019 Elementary Particles Presentation by Smriti and Priyanka

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Shri Agrasen KanyaAutonomous

P.G. College, Varanasi

External Supervisor Internal Supervisor

Dr. Shubha R. Saxena (HOD)

Dr. Sunil Mishra

Shri A. K. A. P. G. olle!e

"aranasi

Sub#itte$ b%

Pri%an&a "er#a

S#riti Sin!h

'. S. (inal *ear)

A Pro+et on, Ele#entar% partiles

Sub+et,- Ph%sis

Session, /01-02

'ahelor o3 Siene

In

Ph%sis


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ACK(&)*EDGEE(T

+ am than"ful to our Princi%al /r.

Kum"um al'iya( + am #ee%ly in#e&te#&y our am /r. Shu&ha 3 Sa4ena 5ea#(of /e%artment of Physics( Shri A. K. A.P.G. College( Varanasi for ins%iring an#%ro'i#ing im%ortant &oo"s S. 6. Ghosal(

S.Chan# - /a'i# Gri7th for this )or".+ am than"ful to res%ecte# teacher /r.Sunil ishra /e%artment of Physics( ShriA. K. A. P.G. P.G. College( an# Varanasifor hel%ing me lots &y8 gi'ing suggestion

an# gui#ance.+ am heartily than"ful to all our teachersof the #e%artment )hose great &lessingan# lo'e ma#e it %ossi&le for me to goan# succee#e# in my )or".

Priyan"a Verma- SmritiSingh

.Sc. 9Physics:

inal year


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I(TR&DCTI&(Matter in this universe is supposed to be

made of microscopic elementaryconstituents these particles are known aselementary particles. A few of them suchas !roton Electron are stable but most

of them decay soon after their production


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Elementary or-unamental /arti0les

An elementary particle isone which is not a compositeof others, i.e., whose internal

structure cannot be describeas a combination of otherparticles.

In early 30’s people knew

about only four elementaryparticles-the electron, theproton, the neutron and the

photon. This number hadgrown to ! by "!# and to3$ by "%#.


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Chara0teristi0 /ro/ertieso- elementary /arti0les

ass;


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Intera0tionsGra'itational interactions

It is the weakest interaction which isattracti&e and uni&ersal.

!ea" interactionsThese interaction cause the light particles to

interact with one another and with hea&ierparticles.

$lectromagnetic interactionsIt is similar to the gra&itational interactions

but depends upon the nature of charges onthe particles.

Strong interactionsIt is the dominant interaction in high-energy

particles physics. These are also callednuclear interaction.The relati&e magnitudes of gra&itational,

weak, electromagnetic and stronginteractions are in the ratio

0-3"

0-3

0-3


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PARTIC*ES A(D

A(TI1PARTIC*ES

2irac predicted theoretically the eistence ofantiparticles for the electron. 7e actuallypostulated that e&ery particle has antiparticles.The antiparticles of a gi&en particles has eactlythe same mass, spin, and life time *if unstable+but an opposite charge *if any+.

$lectron an# %ositron

The first antiparticles known was positron whichwas disco&ered by Anderson in "3$. It is apositi&ely charged electron, i.e., it has the samemass and the same spin as an electron butopposite charge. 8hen an electron and a positroncome in contact with each other.e( ( e- 9 $@

Proton an# anti%roton

The antiparticles of proton are called theantiproton. It has the same mass as a proton, butan opposite charge and the same spin as a protonbut an opposite magnetic moment. Thus it is anegati&e proton and is denoted by p- . It wasestablished in"%% by :egre, ;hamberlain and

their collaborators.


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6eutron an#antineutronIt is much harder to detect an antineutron

because it has no charge. 5oth neutronand antineutron ha&e )ero charge and thesame mass but antineutron is supposed toha&e an internal charge distribution tothat of neutron.

6eutrino an#

antineutrinoThe antiparticles of neutrino & areantineutrino. The neutrino spins counterclockwise when &iewed from behind from

behind, while antineutrino spins clockwise.


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Classi20ation o-elementary /arti0les

n the &asis of thecharacteristic %ro%erties suchas mass( s%in( intrinsic angularmomentum an# the nature of

reactions they can un#ergo(the elementary %articles areusually classi,e# into follo)inggrou%s.


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Photons4hoton is a 'uantum of electromagnetic radiation. It isa stable particle with )ero charge and )ero rest mass.It is a bosom because its spin is unity. It has energy

gi&en by 4lanck’s e'uation 69h& where & is thefre'uency of radiation. It has an e'ui&alent mass gi&enby 6instein e'uation 69mc$. therefore(

*e/tonsThese are light weight elementary particles. They ha&ea spin e'ual to and are, therefore, fermions. They

are characteri)ed by their :pin-momentum .The leptons are

stable ecept muons. They interact weakly with otherparticles and occur as particles and antiparticles.

The members of lepton class are electron and positron

*e- , e(+, muons * - , (+, electron-neutrinos *&e, e+ andmuon-neutrinos *& , +.

Ele0tron an /ositron6lectron is stable atomic particles of mass ".0-3 kgand negati&e charge of .


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uons $or 31esons'Mu-mesons, called muons, were disco&ered by Anderson in"3


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esons =esons are the agent of interaction between particles inside the nucleus.Their eistence was predicted by @ukawa in his meson theory of nuclearforces.=esons are middle weight particles ha&ing masses intermediate between theelectrons and protons. They are all bosons ha&ing )ero spin. They possess )erointrinsic *spin+ angular momentum and are unstable.

>ariety of mesons is now known. They include

5 6 1mesons or /ions-mesons were disco&ered in "!# in the cosmic rays. They can eist in threestates (, - and 0. The ( and - are antiparticles of each other while 0*neutral pi-meson+ has no charge and it is its own anti particle. ( and - mesons ha&e a rest mass of $#3 me *me being rest mass of electron+

while the rest mass of (

meson is slightly less, e'ual to $+protons with nucleons *proton or neutron+ according to the following

p ( p 9 p ( n ( (

p ( n 9 p ( p ( -

p ( p 9 p ( p ( 0

They are also produced by annihilation of proton-antiproton and neutron-antineutron

p ( p- 9 ( ( - ( 0

n ( n 9 ( ( - ( 0

The -mesons are unstable particles. The a&erage life time of charged -mesons *0 and -+ is of the order of 0- sec while that of neutral -mesons*0+ is still shorter *9"0-#sec+. ;onse'uently, only a fraction of cosmic ray -mesons can reach and they decay in flight by weak interaction intocorresponding muons and -neutrinos

B( - ( ( - - - (

( and - further decay into e( and e- respecti&ely.The neutral -meson *0+ decays by an electromagnetic interaction into twohigh energy -photons@ - (@ @


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K1esons $or Kaons'

D-=esons is a hea&ier class of mesons.They eist as D( and its antiparticles k- andalso as k0 and its antiparticles 0.The charged D-mesons *D( and D-+ ha&e restmasses of "


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9aryons

There are hea&y weight elementary particles,ha&ing their rest mass e'ual to or greater thanthat of nucleon *4roton and neutrons+, but less

than that of deuteron. They ha&e spin &alues ofand hence are fermions. They are strongly

interacting and posses intrinsic angularmomentum 6cept protons, all baryons are unstable.

5aryons ha&e been grouped into two subclasses;6ucleons

These are nuclear particles and include proton*p+, neutron *n+ and their anti particles, antiproton and anti neutron . 4roton has a mass

3< me while neutron’s mass Is 3" me. Theyall ha&e a spin of and are fermions.5y%erons

The baryons possessing the rest mass greaterthan that of nucleons are called hyperons. Theyare unstable and ha&e an a&erage life time of

the order of 0-0 sec. Their decay time is &erymuch greater than the time of their formation*0-3 sec+. Therefore, these particles, along withthe D-mesons are called strange particles.


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There are four types of hyperons*am"a hy/erons $:;'41 There are

t)o lama hy%erons( )hich ha'e

Dero charge an# 21E1 me( rest mass. They are re%resente# &y B0 an# <one is anti %articles of the other.

Sigma %y/erons4 < There are si4%articles F( H


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Conser!ation la7sgo!erning elementary/arti0les

The production and decay of elementaryparticles is go&erned by certainconser&ation laws. The applications ofthese laws ha&e led to the disco&ery of

new fundamental particles. Thedisco&ery of neutrino in -decay is suchan eample. In fact, by assuming the&alidity of these laws, many of thefundamental particles were firstpredicted theoretically and thendisco&ered eperimentally. Theseconser&ation laws are essential featuresof all interactions and are listed below

;onser&ation of electric charge;onser&ation of mass energy;onser&ation of linear momentum;onser&ation of angular momentum

*spin+


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*a7 o- 0onser!ation o-*e/ton1(um"er

According to this law, in anyprocess the total lepton number isalways conser&ed. It includes theconser&ation of electron-lepton

number *F+ and conser&ation ofmuon-lepton number *=+.F 9 ( for electron and e-neutrino*e- and &e+

F 9 - for anti leptons *e( and &e+F 9 0 for all other particles.

:imilarl@, muon-lepton number.= 9 ( for meson and neutrino= 9 - for their antiparticles= 9 0 for all other particles.


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*a7 o- 0onser!ation o-"aryons num"er

According to this law, in any process,the total baryon number is alwaysconser&ed. ;on&entionally, the baryonnumber5 9 ( for baryons5 9 - for anti baryons5 9 0 for all other particles

As an eample, consider the decay ofneutron

?0 - p( ( e- ( e1or it 5 9 - 0 ( 0


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Elementary Particles Presentation by Smriti and Priyanka

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