2.3 Leptons at work

Question 1

What is produced from a single electron-positron annihilation event

Answer 1

A quark and an antiquark is produced which move away in opposite directions, producing a shower of hadrons in each direction

Question 2

Are the neutrinos and antineutrinos produced in beta decays were different from those produced by muon decays?

Answer 2

NONONONONONO

Question 3

If there were only one type of neutrino and antineutrino, equal numbers of…

Answer 3

… electrons and muons would be produced

Question 4

Symbol for the muon neutrino

Answer 4

vμ

Question 5

Symbol for the electron neutrino (and similarly for the two types of antineutrinos

Answer 5

ve

Question 6

How can scientists figure out if the universe will continue to expand forever (big yawn) or if it will stop expanding and contract (big crunch)

Answer 6

If the rest mass of the neutrinos can be measured accurately

Question 7

What can leptons change into

Answer 7

Other leptons through the weak interaction and can be produced or annihilated in particle-antiparticle interactions

Question 8

In an interaction between a lepton and a hadron, a neutrino or antineutrino can change into or from a corresponding charged lepton. Electron neutrino can interact wit neutron:

Answer 8

ve + n –> p + e-

Even though charge is conserved, an electron neutrino and neutron could not change into antiproton and positron:
_
ve + n -/-> p + e+

By assigning +1 to lepton, -1 to antilepton and 0 to any non-lepton, cam see that charge in first eq. before and after change is +1, this is permitted. and in second eq, +1 to -1. This is not permitted

Question 9

In muon decay the muon changes into a muon neutrino. Also, an electron is created to conserve charge and a corresponding antineutrino is create to conserve lepton number Eg:

Answer 9

_
μ- –> e- + ve + vμ

However, muon cannot decay into muon antineutrino, electron and electron antineutrino through charge is conserved

μ- -/-> e- + ve + vμ

First equation has lepton number of + 1 before change and lepton number of +1 after change, equation is permitted. Second equation has lepton number of +1 before change and -1 after change. This is not permitted

Question 10

The lepton number is…

Answer 10

… conserved in any change

Question 11

Why is
_
μ- –> e- + ve + vμ

never seen

Answer 11

The muon can only change into a muon neutrino

Muon can’t change into a muon antineutrino and an electron can only be created with an electron antineutrino

Question 12

The lepton number is ______ for any lepton, ______ for any antilepton and ______ for any non-lepton

Answer 12

+1
-1
0