Neutrino Physics. Kam-Biu Luk. Tsinghua University and University of California, Berkeley and Lawrence Berkeley National Laboratory

Transcription

1 Neutrino Physics Kam-Biu Luk Tsinghua University and University of California, Berkeley and Lawrence Berkeley National Laboratory 4-15 June, 2007

2 Outline Brief overview of particle physics Properties of neutrino Production of neutrino Detection of neutrino Massive neutrinos 2

3 References Spaceship Neutrino, by C. Sutton, Cambridge University Press, A popular science book on the history of neutrino. Nuclear and Particle Physics: An Introduction, by B.R. Martin, Wiley, A textbook for undergraduate students. Elementary Particles and Their Interactions: Concepts and Phenomena, by H.K. Quang and X.Y. Pham, Springer, A textbook on particle physics for advanced undergraduate and graduate students. Current Aspects of Neutrino Physics, ed. D. Caldwell, Springer, A reference overviewing the field of neutrino physics for researchers. Physics of Massive Neutrinos, 2nd.ed., by F. Boehm and P. Vogel, Cambridge University Press, A reference on neutrino physics for researchers. 3

4 A Quick Tour of Particle Physics 4

5 What Are The Basic Building Blocks? Ancient ideas: Greek (Aristotle) Chinese 5

6 (particle) (particle) 6

7 Current Basic Building Blocks of Matter Electric charge in unit of e : 2/3-1/3-2/3 1/ A particle and its antiparticle have the same mass All quarks and leptons are spin-1/2 particles 7

8 Some Units And Convention Unit of energy used in nuclear and particle physics: electron volt (ev) 1 ev = energy gained by a particle of charge e after accelerated through a potential difference of 1 V 3 1keV = 10 ev = ( C) 1 V = MeV = 10 ev J 9 1GeV = 10 ev We often take energy units as mass units: E = mc 2 ; c = 1 1 ev/c 2 1 ev = kg 1TeV = ev Relation between energy and distance: Planck constant, h = J-s Reduced Planck constant, h = h 2" =1.05 #10$34 J - s hc " h =197 #10 $15 MeV % m =197 MeV % fm 8

9 Quarks And Leptons 9

10 Spin A kind of angular momentum Fermions: 1/2, 3/2, Bosons: 0, 1, Spin ½ Left-handed state Right-handed state 10

11 quarks Quarks Carry Colour Antiquarks u u u up u u u d d d down d d d c c c charm c c c s s s strange s s s t t t top t t t b b b bottom b b b 11

12 Baryons: Hadrons: Strongly Interacting Particles Proton Λ Antiproton Mesons:! + 0! Hadrons are colourless! 12

13 Fundamental Forces (Interactions) Gravitation Electromagetism deuteron neutron proton 212 Po 208 Pb + α(8.95 MeV) Strong Weak 13

14 Feynman diagram: Interactions of Particles time particle antiparticle displacement Strong Electromagnetic Weak q 1 q 2 e e ν, e e, d Gluon g photon γ Z, W - q 1 q 2 e e ν e, u 14

15 Summary of Force Carriers 15

16 Standard Model Generation I Generation II Generation III Leptons! e e! µ µ "!! Assume: m ν = 0 Quarks u u u c c c t t t d d d s s s b b b Gauge Bosons 0 Z W + W!! gluons 16

17 Lepton Numbers Base on observations, in the Standard Model, : L e = 1 for e -, ν e such that Δ L e = 0 L μ = 1 for µ -, ν μ such that Δ L μ = 0 L τ = 1 for τ -, ν τ such that Δ L τ = 0 e.g. tau lepton decay: " # $ µ # + % µ + % " tau lepton number L τ : muon lepton number L µ : " + # e + + $ e + $ " tau lepton number L τ : electron lepton number L e :

18 Baryon number Observation: proton is stable! proton lifetime, τ p > years Why?? Introduce a quantum number in the Standard Model: quarks antiquarks Baryon number, B: +1/3-1/3 such that All baryons have B = 1 All mesons have B = 0 In any process ΔB = 0 B: 1 0 ΔB 0 18

19 Weak interactions Leptons: 0!1 W - " " " e e µ! µ! # # # W + W bosons transform leptons INSIDE the same generation Quarks: +! u c t W - W + d s b 19

20 Some Weak Decays Leptonic decay: Semileptonic decay: 20

21 Weak Interactions: CC and NC processes Charged Current (CC): - Charged-Current reaction: exchange of W boson - Proposed by Fermi (1934) - Responsible for neutron β decay - Incoming neutrino needs enough energy to produce the outgoing lepton Neutral Current (NC): - Neutral Current reaction: exchange of Z boson - Proposed by Weinberg-Salam - Discovered with neutrinos - Can occur for all flavours 21

22 Some Weak Reactions Involving Neutrinos Inverse beta-decay: Electron capture: 22

23 Summary The Standard Model accounts all the elementary particles known today. Interactions of quarks and leptons are identical However, studies of the neutrinos indicate the Standard Model is incomplete 23