Elementary particles

ELEMENTARY PARTICLESPresented by,[object Object],S.N. Saravanamoorthy M.Sc., M.Phil., B.Ed.,,[object Object],Assistant Professor in Physics,,[object Object],Devanga Arts College (Autonomous),,[object Object],Aruppukottai – 626 101.,[object Object]

1. Introduction,[object Object],2. Classification,[object Object],3. Particles & Antiparticles,[object Object],4. Particles instability,[object Object],5. Conservation laws,[object Object]

INTRODUCTION,[object Object],* By the year 1932, only three elementary particles namely electron, ,[object Object], proton and photon were known.,[object Object],* The discovery of Neutron by Chadwick in 1932 raised their number to ,[object Object], four.,[object Object],* These elementary particles are the building blocks of matter & they ,[object Object], have characteristic properties such as rest mass, electric charge & ,[object Object], intrinsic angular momentum. ,[object Object],* The elementary particles discovered so far, form a long list of ,[object Object], around 200. These particles are elementary in the sense that they ,[object Object], are structureless, i.e., they cannot be explained as a system of ,[object Object], other elementary particles.,[object Object]

Elementary particle,[object Object],Baryons Leptons Mesons Antiparticles,[object Object], Electron Photon Neutron Muon ,[object Object], kaon ,[object Object], Pion Eta,[object Object],Nucleons Hyperons,[object Object],Proton Lambda, Sigma, Omega,[object Object],Neutron,[object Object]

BARYONS (Or) heavy particles,[object Object],* Protons & particles heavier than proton form this group.,[object Object],* Proton and neutron are called nucleons and the rest mass ,[object Object], are called hyperons.,[object Object],* Every baryons has an antiparticle.,[object Object],* If a number, called the baryon number +1 is assigned to ,[object Object], baryons and a number -1 is assigned to antibaryons, then ,[object Object], in any closed system interaction or decay, the baryon ,[object Object], number does not change. This is the law of conservation ,[object Object], of baryons.,[object Object]

HYPERONS,[object Object],* Time decay of the order of 10−10 seconds,[object Object],* Mass value intermediate between neutron & deuteron,[object Object],* Their decay time is very much greater than the time,[object Object], of their formation (10−3 sec).,[object Object],* K mesons – Strange Particles (Gellmann & Nishijima),[object Object],* Four types – Lambda, Sigma, Xi, Omega,[object Object]

Leptons,[object Object],*It contains electron, photon, neutrino & muon.,[object Object],* All these elementary particles have masses smaller,[object Object], than that of a pion.,[object Object],ELECTRON,[object Object],* First discovered particle,[object Object],* negative charge & stable particle,[object Object],* An electrostatic field exists between two electrons,[object Object]

PHOTON,[object Object],* no charge & no rest mass,[object Object],* It has energy given by Plank’s equation E=hν,[object Object],* It has an equivalent mass given by Einstein’s equation,[object Object], E=mc2.,[object Object],NEUTRINO,[object Object],* 1956 – Beta ray spectra in radioactivity,[object Object],* no charge & rest mass is zero,[object Object],* It travels with the speed of light,[object Object],* It exists in two form, one associated with electron & the other with the muon,[object Object]

Muon,[object Object],* It is similar to the electron except that its mass is ,[object Object], about 200 times that of the electron.,[object Object],* It decays very quickly with a half life of 2.2μs into,[object Object], one electron and two neutrinos. ,[object Object],* It is negatively charged and has a spin of ½. ,[object Object],* It was first discovered during the study of cosmic rays.,[object Object]

MESONS,[object Object],* Masses are between those of leptons & baryons.,[object Object],* They are unstable.,[object Object],* They decay into lighter mesons or leptons.,[object Object],* They have either positive, negative at zero charge.,[object Object],* The mesons include the pion, kaon and eta particles.,[object Object]

Positive Pimeson (Pion),[object Object],[object Object]

positively charged particle & life time - 10−8 secNeutral Pion,[object Object],[object Object]

Mass is equal to 264 times the mass of the electronCharged Kaon: +ve charge & a mass of about one-half of ,[object Object], proton.,[object Object],Neutral kaon: No charge & Its life is of the order of 10−9 sec,[object Object]

PARTICLES & ANTI-PARTICLES,[object Object],Electron – Positron,[object Object],* Same mass & the same spin but opposite charge,[object Object],*They annihilate each other with the emission of photons,[object Object],* The existence of an antiparticle for the electron was,[object Object], actually predicted by Dirac, because of a symmetry of ,[object Object], the equations of the relativistic quantum theory of the ,[object Object], electron.,[object Object],[object Object],[object Object]

Neutron and Antineutron,[object Object]

Neutrino and Antineutrino,[object Object],It has Charge Zero, spin ½, zero rest mass and magnetic moment smaller than 10−8 Bohr magneton or nearly zero.,[object Object],Finite energy, momentum and travels with the speed of light. It does not cause ionization on passing through matter.,[object Object],The spin of the neutrino is opposite in direction to the direction of its motion. (neutrino spins – counterclockwise),[object Object],The spin of the antineutrino is in the same direction as its direction of motion. (It spins clockwise),[object Object],The neutrino moves through space in the manner of a left-handed screw, while the antineutrino does so in the manner of a right-handed screw. ,[object Object],Continue…,[object Object]

Neutrino possesses a “left-handed” helicity ; the antineutrino possesses a “right-handed” helicity.,[object Object],Neutrino’s emitted in Beta decay have a negative helicity. ,[object Object],They are longitudinally polarized with their spin axes antiparallel to their direction of travel. ,[object Object],H = + 1 for ν- ; H = - for ν,[object Object],Because of its lack of charge and magnetic moment, a neutrino has essentially no interaction with matter, except that which leads to inverse beta decay. This interaction is extremely weak. (σ≈10- 20 barn),[object Object],Matter is almost totally transparent to neutrinos.,[object Object]

Conservation Laws,[object Object],Conservation of parity,[object Object],Charge conjugation symmetry,[object Object],Time reversal symmetry,[object Object],Combined Inversion of CPT,[object Object]

Conservation of Parity,[object Object],Parity relates to the symmetry of the wave function that represents the system.,[object Object],If the wave function is unchanged then the system has a parity of +1. If changed, then the system has parity of -1.,[object Object],During a reaction in which parity is conserved, the total parity number does not change.,[object Object],Prior to 1956 it was believed that all reactions in nature obeyed the law of conservation of parity.,[object Object],Yang and Lee pointed out that in reactions involving the weak interaction, parity was not conserved.,[object Object],Indeed parity conservation is found to hold true only in the strong and em interactions. ,[object Object]

Charge conjugate symmetry,[object Object],It is the act of symmetry operation in which every particle in a system is replaced by its antiparticle.,[object Object],If the anti-system or antimatter counterpart exhibits the same physical phenomena, then charge parity (C) is conserved.,[object Object],In fact C is not conserved in the weak interaction.,[object Object]

Time reversal symmetry,[object Object],Time parity T describes the behaviour of a wave function when t is replaced by –t. ,[object Object],The symmetry operation that corresponds to the conservation of time parity is time reversal.,[object Object],The direction of time is not significant, so that the reverse of any process that can occur is also a process that can occur.,[object Object],Prior to 1964, time parity T was considered to be conserved in every interaction.,[object Object],One form of Kokaon can decay in to π+, π−, which violates the conservation of T. ,[object Object],The symmetry of phenomena under time reversal does not seem to be universal.,[object Object]

Elementary particles

Elementary particles

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Elementary particles