1900 Charles T. R. Wilson’s ionization chamber Electroscopes eventually discharge even

2. 1900Charles T. R. Wilson’s ionization chamber • Electroscopes eventually discharge even • when all known causes are removed, • i.e., even when electroscopes are • sealed airtight • flushed with dry, • dust-free filtered air • far removed from any • radioactive samples • shielded with 2 inches • of lead! seemed to indicate an unknown radiation with greater penetrability than x-rays or radioactive rays • Speculating they might be extraterrestrial, Wilson ran • underground tests at night in the Scottish railway, but • observed no change in the discharging rate.

3. 1909 Jesuit priest, Father Thomas Wulf , improved the ionization chamber with a design planned specifically for high altitude balloon flights. A taut wire pair replaced the gold leaf. This basic design became the pocket dosimeter carried to record one’s total exposure to ionizing radiation. 0

4. 1909 Taking his ionization chamber first to the top of the Eiffel Tower (275 m) Wulf observed a 64% drop in the discharge rate. Familiar with the penetrability of radioactive rays, Wulf expected any ionizing effects due to natural radiation from the ground, would have been heavily absorbed by the “shielding” layers of air.

5. 1930s plates coated with thick photographic emulsions (gelatins carrying silver bromide crystals) carried up mountains or in balloons clearly trace cosmic ray tracks through their depth when developed • light produces spots of submicroscopic silver grains • a fast charged particle can leave a trail of Aggrains • 1/1000 mm (1/25000 in) diameter grains • small singly charged particles - thin discontinuous wiggles • only single grains thick • heavy, multiply-charged particles - thick, straight tracks

6. November 1935 Eastman Kodak plates carried aboard Explorer II’s record altitude (72,395 ft) manned flight into the stratosphere

7. 1937 Marietta Blau and Herta Wambacher report “stars” of tracks resulting from cosmic ray collisions with nuclei within the emulsion Cosmic ray strikes a nucleus within a layer of photographic emulsion 50mm

8. Elastic collision

9. p p p p p p

10. 1894After weeks in the Ben Nevis Observatory, • British Isles,Charles T. R. Wilsonbegins • study of cloud formation • a test chamber forces trapped moist air to expand • supersaturated with water vapor • condenses into a fine mist upon the dust • particles in the air • each cycle carried dust that • settled to the bottom • purer air required larger, • more sudden expansion • observed small wispy trails • of droplets forming without • dust to condense on!

12. Tracks from an alpha source

17. boiling begins at nucleation centers (impurities) in a • volume of liquid • along ion trails left by the passage of charged particles • in a superheated liquid tiny bubbles form for ~10 msec • before obscured by a rapid, agitated “rolling” boil • hydrogen,deuterium,propane(C3H6)or Freon(CF3Br) • is stored as a liquid at its boiling point by external • pressure (5-20 atm) • super-heated by sudden expansion created by piston or • diaphragm • bright flash illumination and stereo cameras record 3 • images through the depth of the chamber (~6mm • resolution possible) • a strong (2-3.5 tesla) magnetic field can identify the • sign of a particle’s charge and its momentum (by the • radius of its path) • 1960 Glaserawarded the Nobel Prizefor Physics 1952 Donald A. Glaser invents the bubble chamber

19. Side View 3.7mdiameter Big European Bubble Chamber CERN (Geneva, Switzerland) Top View

22. Primary proton 1936 Millikan’s group shows at earth’s surface cosmic ray showers are dominated by electrons, gammas, and X-particles capable of penetrating deep underground (to lake bottom and deep tunnel experiments) and yielding isolated single cloud chamber tracks

23. 1937 Street and Stevenson • 1938 Andersonand Neddermeyer • determine X-particles • are charged • have 206× the electron’s mass • decay to electrons with • a mean lifetime of 2msec 0.000002 sec

24. Schrödinger’s Equation Based on the constant (conserved) value of the Hamiltonian expression total energy  sum of KE + PE with the replacement of variables by “operators” As enormously powerful and successful as this equation is, what are its flaws? Its limitations?

25. We could attempt a RELATIVISTIC FORM of Schrödinger: What is the relativistic expression for energy? relativistic energy-momentum relation As you’ll appreciate LATER this simple form (devoid of spin factors) describes spin-less (scalar) bosons For m=0 this yields the homogeneous differential equation: Which you solved in E&M to find that wave equations for these fields were possible (electromagnetic radiation).

26. (1935)Hideki Yukawa saw the inhomogeneous equation as possibly descriptive of a scalar particle mediating SHORT-RANGE forces like the “strong” nuclear force between nucleons (ineffective much beyond the typical 10-15 meter extent of a nucleus For a static potential drop and assuming a spherically symmetric potential, can cast this equation in the form: with a solution (you will verify for homework): h mc whereR=

27. h mc Let’s compare: whereR= to the potential of electromagnetic fields: with e-r/R=1 its like R orm = 0! For a range something like 10-15 m Yukawa hypothesized the existence of a new (spinless) boson with mc2 ~ 100+ MeV. In 1947 the spin 0 pion was identified with a mass ~140 MeV/c2

28. 1947 Lattes, Muirhead, Occhialini and Powell observe pion decay Cecil Powell (1947) Bristol University 

29. C.F.Powell, P.H. Fowler, D.H.Perkins Nature 159, 694 (1947) Nature 163, 82 (1949)

30. Quantum Field Theory Not only is energy & momentum QUANTIZED (energy levels/orbitals) but like photons are quanta of electromagnetic energy, all particle states are the physical manifestation of quantum mechanical wave functions (fields). Not only does each atomic electron exist trapped within quantized energy levels or spin states, but its mass, its physical existence, is a quantum state of a matter field. the quanta of the em potential  virtual photons as opposed to observable photons These are not physical photons in orbitals about the electron. They are continuously and spontaneously being emitted/reabsorbed. e-

31. The Boson Propagator What is the momentum spectrum of Yukawa’s massive (spin 0) relativistic boson? Remember it was proposed in analogy to the E&M wave functions of a photon. What distribution of momentum (available to transfer) does a quantum wave packet of this potential field carry? qr = qrcos dV = r2 d sin d dr Integrating the angular part: 2 The more massive the mediating boson, the smaller this distribution…

32. Consistently ~600 microns (0.6 mm) 

41. pdg.lbl.gov/pdgmail

42. BraKet notation We generalize the definitions of vectors and inner products ("dot" products) to extend the formalism to functions (like QM wavefunctions) and differential operators. v = vxx + vyy + vzzSnvnn then the inner product is denoted by vu = ^ ^ ^ ^ Snvnun ^ ^ Remember: nm = nm sometimes represented by row and column matrices: [vxvyvz] ux uy= [ ] uz vxux + vyuy + vzuz

43. We most often think of "vectors" in ordinary 3-dim space, but can immediately and easily generalize to COMPLEX numbers: vu =Sn [vxvyvz] ux uy = [ ] uz Snvn*un * * * vx*ux + vy*uy + vz*uz transpose column into row and take complex conjugate and by the requirement < v| u> = < v| u>* we guarantee that the “dot product” is real

44. Every “vector” is a ket : |v1> |v2> including the unit “basis” vectors. We write: | v > = Sn| > and the scalar product by the symbol < | > and the orthonormal condition on basis vectors can be stated as < | > = d Now if we write |v1> = SC1n|n>and |v2> = SC2n|n>then “we know”: < v2 | v1 > = SnC2n*C1n = S < v2 | | v1 > = “bra” Cnn v u m n mn Sn,mC2m* C1n<m|n> because of orthonormality SmC2m* <m|SnC1n|n>

45. C1n So what should this give? < n | v1 > = ?? So if we write |v > = SCn|n> = Sn|n> = Sn = {Sn } = <n|v> |n><n|v> 1 |v> |v> |n><n| |v> Remember: < m | n > gives a single element 1 x 1 matrix but: | m > < n | gives a???

46. Sn|n><n| In the case of ordinary 3-dim vectors, this is a sum over the products: [ 1 0 0 ] [ 0 1 0 ] [ 0 0 1 ] 1 0 0 0 1 0 0 0 1 + + 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 = + + 1 0 0 0 1 0 0 0 1 =

47. Two important BASIC CONCEPTS • The “coupling” of a fermion • (fundamental constituent of matter) • to a vector boson • (the carrier or intermediary of interactions) e- • Recognized symmetries • are intimately related to CONSERVED quantities in nature • which fix the QUANTUM numbers describing quantum states • and help us characterize the basic, fundamental interactions • between particles

48. Should the selected orientation of the x-axis matter? As far as the form of the equations of motion? (all derivable from a Lagrangian) As far as the predictions those equations make? Any calculable quantities/outcpome/results? Should the selected position of the coordinate origin matter? If it “doesn’t matter” then we have a symmetry: the x-axis can be rotated through any direction of 3-dimensional space or slid around to any arbitrary location and the basic form of the equations…and, more importantly, all the predictions of those equations are unaffected.

49. If a coordinate axis’ orientation or origin’s exact location “doesn’t matter” then it shouldn’t appear explicitly in the Lagrangian! EXAMPLE:TRANSLATION Moving every position (vector) in space by a fixed a (equivalent to “dropping the origin back” –a) –a original description of position r r' or new description of position

50. For a system of particles: function of separation acted on only by CENTAL FORCES: no forces external to the system generalized momentum (for a system of particles, this is just the ordinary momentum) for a system of particles T may depend on q or r but never explicitly on qi or ri =