1. Before class experiment #1: Cloud chamber reveals tracks of charged particles

2. Before class experiment #2: Muon cosmic ray telescope
...half life of muon at rest = 2 micro sec even at speed of light.  At 1 nanosec/foot, muon only goes 2000 feet
how does muon get here from top of atmosphere? 7 miles up (time dilation...see next lecture)
every second a cosmic ray muon pierces you...

3. Weak (Radioactive) Interaction: Power and Longevity of the Sun
if 6 kinds of quarks and 6 types of leptons, why only see up and down quark and electron?

weak interactions cause massive quarks and leptons to decay into lighter quarks and leptons
weak interactions cause quark or lepton to transform via W and Z force carrying particles

Why is sun 4.5 billion years old? slowness of weak interaction
Where does it get its power? nuclear fusion converting mass to energy... ultimate source of all our energy
pp -> (pn) e⁺ v= d e⁺ v                 d= deuteron = ²H¹₁ = n+p

4. Radioactive Beta Decay of the Neutron ... Classic Weak Interaction
neutron (udd) decays to a proton (uud) + electron + e-antineutrino
decay electrons initially called "beta rays" / didn't know they were electrons
intermediate stages occur in <10^-27 , second not observable

5.Particle Decay Mediators
nucleus can decay into less massive nucleus by splitting apart
how can a fundamental particle decay into another fundamental particle?
a particle can decay into less massive particle + force-carrier ( W or a gluon) boson
boson then decays into other particles / mediating particle decays / seems to violate conservation of energy because their high mass, but "virtual" bosons exist so briefly no "rule" broken

6. Uncertainty and Virtual Particles
1927- Heisenberg's formulation of a fundamental property of quantum mechanics:
it is impossible to measure both a particle's position and its momentum exactly
the more precisely we determine one, the less we know about the other , and 
7. Neutrinos
have no charge, and little, if any, mass / almost never interact with other particles / pass right through earth without interacting / 1/sec pass through you...and only one will interact in your lifetime / produced only in weak interaction decays
observation of radioactive decay of neutron reveals the neutrino's existence.

sum of momenta of electron and proton not equal to the original momentum of the neutron
some other particle accounts for the missing momentum: the neutrino

neutrinos: produced by weak interactions in stars and supernova, 99% of energy a lot of them in the Universe like 3 degree big bang photons

8. Antimatter
every particle (matter) has corresponding antiparticle (antimatter), the electron (e^-) antiparticle is a positron (e⁺)

antiparticles are same as corresponding matter particle, except all charges opposite e.g. proton is electrically positive; anti-proton is electrically negative, but both have exactly same mass and affected in the same way by gravity

when particle and its antiparticle meet, annihilate into pure energy which this energy may materialize into any particle/anti-particle pair, or into neutral force-carrier particles, such as photons, Z bosons, or gluons

9. Anti-proton Annihilations in Hydrogen
photograph of antiproton colliding with a proton in liquid hydrogen / eight pions produced / one pion decays into muon and neutrino positive and negative particles curve in opposite directions in magnetic field

bubble chamber more advanced detector than cloud chamber, but much less powerful than modern detectors ...see cloud chamber in class experiment

10. Discovery of Top ...March 1995...one of first events:
top quark --> bottom quark + W⁺ --> e⁺ + neutrino / bottom quark emerges as neutral anti-B meson and decays into Jet 4
antitop quark --> antibottom quark + W^- --> anti-up quark + down quark/antibottom quark (B^o meson) decays into Jet 1
cannot tell which of Jets 2 and 3 is the anti-up quark and which is the down quark
bottom & antibottom meson have long lifetimes and enough energy to travel visible distance before decay / both emerge as neutral particles, neither leave tracks until they decay
neutrino leaves no track, presence is inferred by missing momentum and energy

11. Annihilation of Antimatter Positron Electron Tomography
Example: e⁺ + e^- --> + (photon + photon) / Experiment:  ²²Na nucleus (in salt) is unstable, emitting positron / positron finds an electron in NaCl / crystal annihilation produces 2 back-to-back gamma rays

12. Positron Emission Tomography
Application:  ingested radioactive salt is rapidly metabolized, concentrated by cancer / trace back 2 gamma rays to source with < 1mm accuracy, before tumor metastasizes
physicists can also annihilate two particles of tremendous energies to create new, massive particles

13. Electromagnetism ... the second step on the road to unification
first: Newton unified planetary & terrestrial gravity
Maxwell: second unification of forces - electricity and magnetism / electrical charge (positive/negative) and magnetism (north/south) are different aspects of the same force
photons absorbed or radiated by any accelerating electrically charged particle
photons have zero mass / always have the speed c = 300, 000, 000 m/s in a vacuum ...in any frame of reference!!!
...and they behave as particles...see in-class experiment

14. Photons as Particles... in-class experiment
absorb light and see decrease of signal in detector / number of photons decreasing, not energy of each, until reach a minimum size pulse...cannot get 1/2 / photon more attenuation, fewer photons, but all of same energy

15. Unified Electroweak Interaction
weak charges closely related to electromagnetic charges / force not actually small at very short distances, where weak interaction comparable to electromagnetic.

difference in strength due to huge difference in mass between W and Z, (very heavy) and massless photon

Next unifications in progress 1) electroweak with strong (Grand Unified Theory (GUT)) 2) electroweak/strong with gravity (string theory) ...again, another Nobel prize for your generation

16. Grand Unification Theory
theory which (we hope!) unifies the strong, weak, & electromagnetic interactions, more data is needed to tell which of many theories describes nature

all interactions we observe appear to be different aspects of the same, unified interaction / current data and theory show that all forces merge into one force at a high enough energy, at small distances, and at early times in the universe

this primordial force-carrier particles would cause the proton to decay / such decays extremely rare; otherwise our world would not exist today/ and asymmetric, otherwise universe would not be dominated by matter, rather than antimatter.

17. Summary: A Short History of the Universe
The active forces and particle in each era: big bang, age of leptons, age of nucleons, age of ions, age of atoms, and age of stars