Phy107Spr06Lect36

Phy107Spr06Lect36 - From Last Time Neutrino N e u t rin o w...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Mon. Apr. 24, 2006 Phy107 Lect. 36 1 From Last Time… • Particles are quanta of a quantum field – Represent excitations of the associated field – Particles can appear and disappear • Particles interact by exchanging other particles – Electrons interact by exchanging photons • This is the Coulomb interaction • Electrons are excitations of the electron field • Photons are excitations of the photon field Today More particles! Essay due Wednesday Mon. Apr. 24, 2006 Phy107 Lect. 36 2 Neutrino • Neutrino was first detected in 1956 • The neutrino has Zero charge, spin 1/2, almost zero mass • Electron has Charge -e, spin 1/2, mass 0.5 Mev/c 2 • Electron and neutrino generically called leptons But what about protons and neutrons? Fred Reines, Clyde Cowan, at the Hanford nuclear reactor Mon. Apr. 24, 2006 Phy107 Lect. 36 3 Protons/Neutrons are composite Mon. Apr. 24, 2006 Phy107 Lect. 36 4 Protons, neutrons, and quarks • Protons and neutrons are made up of – ‘up’ quarks and ‘down’ quarks Charge +(2/3 )e - (1/3) e Spin 1/2 1/2 Mass (MeV/c 2 ) 3 6 Up Down Mon. Apr. 24, 2006 Phy107 Lect. 36 5 Question A neutron is a composite particle consisting of three quarks (up=charge +2/3e, and down = charge -1/3e). Which is the structure of the neutron. A. up, up, up B. up, up, dow C. up, down, down Total charge : +2e +e 0 Neutron has zero total charge Mon. Apr. 24, 2006 Phy107 Lect. 36 6 Protons & Neutrons To make a proton: We bind 2 up quarks of Q = +2/3 and 1 down quark of Q = -1/3 . The total charge is 2/3 + 2/3 + (-1/3) = +1 ! To make a neutron: We bind 2 down quarks of Q= -1/3 with 1 up quark of Q = +2/3 to get: (-1/3) + (-1/3) + (2/3) = 0 !
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Mon. Apr. 24, 2006 Phy107 Lect. 36 7 Hierarchy of structure R ~ 10 -15 m (strong) protons and neutrons are made from quarks R ~ 10 -10 m (electromagnetic) Atoms are made from protons, neutrons, and electrons R > 10 6 m (gravitational) We’ll talk about the rest of the universe later Mon. Apr. 24, 2006 Phy107 Lect. 36 8 What have we learned? Matter is made of atoms Leptons e ν e Quarks d u “ Atoms are made of leptons and quarks “ Atoms are made of leptons and quarks Bind together to form nuclei, atoms, etc Mon. Apr. 24, 2006 Phy107 Lect. 36 9 What about the muon? • The muon found early on. – Heavy version of the electron. • Otherwise would have been fairly simple! e- μ - e+ μ + μ , Muon mass: 100MeV/c 2 , electron mass 0.5 MeV/c 2 Mon. Apr. 24, 2006 Phy107 Lect. 36 10 More particles • In 1978, the tau was discovered. Just like the electron and muon, but 3500 times heavier than the electron – Same charge, same spin, but different mass. • Made this particle by creating more energy. Both the muon and tau have neutrinos Muon-neutrino Tau-neutrino Mon. Apr. 24, 2006 Phy107 Lect. 36 11 The particle garden • Particle physics at this point has settled on a countable number of ‘fundamental particles’.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

Page1 / 7

Phy107Spr06Lect36 - From Last Time Neutrino N e u t rin o w...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online