1. M. Velasco -- Lecture 1 & 2 Problems – 1.1, 1.2, 1.7, 1.12, 1.13
Introduction – “Historical Overview of Particle Physics, Accelerators and Detectors”
M. Velasco -- Lecture 1 & 2
Problems – 1.1, 1.2, 1.7, 1.12, 1.13

2. Particle Physics
What are the fundamental building “blocks” of the universe ? Visible matter, dark matter, dark energy…
What are the interactions between them? Gravitational, electro-weak, strong…
How can we explain the universe?
its history
its present form
its future
Is there a theory of everything? …bring us back at the beginning of the universe

3. Clear relationship between energy of “particle” and “time”
How we go from tT ? (Boltzman Eq.? Or other gas eq.)

4. What is a particle and how we learn from them?
a small piece of matter...
characterized by
charge
mass
lifetime
spin
particles can scatter off each other like billiard balls
unlike billiard balls, most particles are unstable and decay
particles can be produced by colliding other particles and form bound states

5. Models used to described general principles
Small
Classical
Mechanics
Quantum
Relativistic
Field Theory
Fast
Quantum
Gravity
What is missing? …

6. Quantum Field Theories included in Standard Model
QED=Quantum
Electro Dynamics
QCD=Quantum
Chromo Dynamics
Electro-Weak

7. Production of Particles
Primary cosmic rays:
90% protons, 9% He nuclei
Air nuclei (Nitrogen & Oxygen) + n  K + e+  e _ 
Primaries interact with atmosphere:
Hadronic interaction produces mainly pions (& kaons)
These decay producing a relatively large flux of neutrinos between <100MeV and 104 GeV.
At sea level: c.r. flux approx 1cm-2s-1
The dominating decay sequence is shown, but it is also important to consider the many different decay channels of charged and neutral kaons. (These are significant to neutrino production at high energies)
Nuclear Reactors
 alpha, neutrons, etc.

8. Chronology of Early Discoveries Interplay with introduction of new detectors/particle sources
Electron (1897) J.J. Thompson
Cloud Chamber(1912) C.T.R.Wilson
Cosmic Rays(1913) V.F.Hess &C.Anderson
Discovery of Proton(1919) E. Rutherford
Compton Scattering gege (1923) C.T.R.Wilson
Waves nature of e’s(1927) C. Davisson

9. Cloud Chamber Supersaturated Gas Cloud formation Used until 1950’s
Condensation started around the ions generated by passing charged particles (ionization), and the resulting droplets were photographed. 9

10. Scattering Geiger&Marsden , b Zinc Sulphide Screen E. Rutherford
source
Zinc Sulphide Screen
E. Rutherford
1927, Rutherford, as President of the Royal Society, expressed a wish
for a supply of "atoms and electrons which have an individual energy far
transcending that of the alpha and beta particles from radioactive bodies..."

11. Penetrating Power    Neutron Paper sheet Lead Paraffin Aluminum
Charged particles are characterized by their definite range. Changeless particles including photons are stopped in an exponential manner. Lead though a good shield for Gamma and X-rays, is extremely inefficient in stopping neutrons. Paraffin or polyethylene or hydrogenous materials are good shield for neutrons but bad shield for photons
Neutron
Paper sheet
Lead
Paraffin
Aluminum

12. Cross-Section Approximately the area of a proton Radii of nuclei ~ fm
1 barn =10-24 cm2
Approximately the area of
a proton
Radii of nuclei ~ fm
Distribution of scattering angles tell us about the force/particles
Precision required

13. Accelerator technology
The first successful cyclotron, built by Lawrence and his graduate student M. Stanley Livingston, accelerated a few
hydrogen-molecule ions to an energy of 80,000 electron volts. (80KeV)
MeV

15. Particle guidance
In circular machines use magnetic field to guide particles along orbit (Lorentz force)
in early machines e.g. cyclotrons B field occupied entire accelerating plane
What about machines with larger energies like the one we need today?
Can you guess based on your basic knowledge of E&M ?

16. Kinematics of circular accelerators
Use relativistic equations of motion (v = c)
Centripetal force = Lorentz force (magnetic)
mv2/r = mv = qvB/c v  B  = 1/(1 - v²/c²)
 rev. freq.  = /2 = qB/2mc
at relativistic speeds v = c and momentum P = mc
  = c/2 = qB/2P  = radius of orbit
 P = qB/c
or, P (GeV/c) = 0.3 B (Tesla)  (m) ( q = e )
In another words,  = (q/2mc) (1 - v²/c²) B
as particle accelerates, v increases,  B and/or  must increase to compensate
in electron synchrotrons (LEP)  fixed , B increases

17. Summary of what the world was made of by 1932
electrons (1897)
orbit atomic nucleus
photon (1905)
quantum of the electromagnetic field
proton (1911)
nucleus of lightest atom
neutron (1932)
neutral constituent of the nucleus
 Required new experimental techniques...not stable … more questions

18. Postulates  to explain what was observed & known at that time
1927 Dirac’s relativistic quantum mechanics
antiparticles: for every particle there exists an antiparticle with same mass, lifetime, spin, but opposite charge
1931 the positive electron (positron) found
1930 Pauli’s neutrino
energy conservation in beta (b) decay requires the existence of a light, neutral particle
n  p+ + e- +  (e- = b)
observed in 1956  Why it took so long?
… To come …1937 Yukawa’s pion to explain inter-nuclear forces

19. E2 – p2c2 = (m0c2) 2 “relativistic invariant”
Just as the equation x2=4 can have two possible solutions (x=2 OR x=-2), so Dirac's equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy.
Dirac interpreted this to mean that for every particle that exists there is a corresponding antiparticle, exactly matching the particle but with opposite charge. For the electron, for instance, there should be an "anti-electron" called the positron identical in every way but with a positive electric charge.
E2 – p2c2 = (m0c2) 2 “relativistic invariant”
(same value in all reference frames)

20. 1931 the positive electron (positron)

21. Neutrinos must be present to account
for conservation energy & momentum __
Wolfgang Pauli
Large variations in the emission velocities of the  particle seemed to indicate that both energy and momentum were not conserved.
This led to the proposal by Wolfgang Pauli of another particle, the neutrino, being emitted in  decay to carry away the missing mass and momentum.

22. 1937: Theory of nuclear forces
Hideki Yukawa
Existence of a new light particle (“meson”)
as the carrier of nuclear forces (140GeV)
Relation between interaction radius & meson mass m:
mc2  200 MeV
for Rint  cm
Since t = hbar/mc^2, and boson travels < c, max distance R = ct = hbar c/MeV. Nuclear force only 10^-12cm, so pion has mass 140 GeV.

23.
Neutron(1932) J. Chadwick
Triggered Cloud Chamber(1932) P.Blackett
Muon(1937) S.H. Neddermeyer
Muon Decay(1939) B.Rossi, Williams
Kaon(1944) L. Leprince-Ringuet
Pion(1947) H.Perkins,G.P.S.Occialini

24. Emulsion heavily used in the early days of Cosmic Ray experiments
Dates back to Becquerel (1896)
Three components
silver halide (600mm thick)
plate
target
Grain diameter 0.2mm
Still the highest resolution device

25. Emulsion  used in discovery of m, p, k, etc.
Scale 100mm

26. The particle “Zoo”  Cosmic rays 1st , followed by accelerator
1947: strange particles
K0+ -, K++ + -
p+ -
, 
long lifetime  ~ s
more particles...
p,

short lifetime  ~10-24 s

27.
Efficient production of particles with higher masses is going to required high energy
Before 50’s E=mc2 was still just a theory…
Next period will required the development of both accelerators in addition to detectors
Cockcroft and Walton…

28. Energy and momentum for relativistic particles
(velocity v comparable to c)
Speed of light in vacuum c = x 108 m / s
Total energy:
m: relativistic mass
m0: rest mass
Expansion in powers
of (v/c):
energy
associated
with rest mass
“classical”
kinetic
energy
Momentum:

29. E = mc2 Cockcroft & Walton Accelerator
First artificial splitting of nucleus
First transmutation using artificially accelerated particles
First experimental verification of
E = mc2

30. Relativity “Mass” not conserved  Energy & Momentum are conserved
Experimental verification of E = mc2
17.3 MeV
1 MeV
Proton + Lithium a particles + Energy

31. Other discoveries between 1947-1953
Scintillation Counters(1947) F. Marshall
pion decay(1947) C. Lattes
Unstable V’s(1947) G.D.Rochester
Semi-Conductor Detectors(1949) K.G.McKay
SparkChambers(1949) J.W.Keuffel
K Meson decays(1951) R.Armenteros

32. Basic principles of particle detection
Passage of charged particles through matter
Interaction with atomic electrons K p
ionization
(neutral atom  ion+ + free electron) p e
excitation of atomic energy levels
(de-excitation  photon emission) m
Ionization + excitation of atomic
energy levels energy loss
Momentum
Mean energy loss rate – dE /dx
proportional to (electric charge)2
of incident particle
for a given material, function only
of incident particle velocity
typical value at minimum:
-dE /dx = 1 – 2 MeV /(g cm-2)
What causes this shape?

33. Most detectors at that time based on Ionization
Charged particles
interaction with material + -
“track of ionisation”

34. Mean ionization potential
Density of electrons
Important for all charged particles
Bethe-Bloch Equation
velocity
Mean ionization potential
(10ZeV)

35. Ionization
In low fields the ions eventually recombine with the electrons
However under higher fields it is possible to separate the charges
Note: e-’s and ions generally move at a different rate - - - - - - - - - - - - - + + + E + + + + +

36. 1953-1968 Neutrino (1953) F. Reines Bubble Chamber(1953) D.A. Glaser
K+ Lifetime(1955) L.W.Alvarez
Flash Tubes(1955) M. Conversi
Spark Chamber(1959) S. Fukui
Streamer Chambers(1964) B.A.Dolgoshein
MWPC(1968) G. Charpak

37. CERN SLAC LEP-1984-1999 SC 1957-1990 Synchrotron Radiation
The Stanford two-mile electron linear accelerator (SLAC)
SLAC

38. Before we move to accelerator based measurement let’s talk about neutrinos - n  Puzzle in b – decay: the continuous e- energy spectrum
First measurement
by Chadwick (1914)
Radium E: 210Bi83
(a radioactive isotope
produced in the decay chain
of 238U)
If  – decay is (A, Z)  (A, Z+1) + e–, then the emitted electron
is mono-energetic  e- total energy E = [M(A, Z) – M(A, Z+1)]c2
(neglecting the kinetic energy of the recoil nucleus ½p2/M(A,Z+1) << E)

39. Theory of -decay - decay: n  p + e- + 
Enrico Fermi
Theory of -decay
- decay: n  p + e- + 
+ decay: p  n + e+ +  (e.g., 14O8  14N7 + e+ + )
: the particle proposed by Pauli
(named “neutrino” by Fermi)
: its antiparticle (antineutrino)
Fermi’s theory:  particles emitted in  – decay need not
exist before emission –
they are “created” at the instant of decay
Prediction of  – decay rates and electron energy spectra as a function of only one parameter: Fermi coupling constant GF (determined from experiments)

40. First neutrino detection
(Reines, Cowan 1953)
E = 0.5 MeV
 + p  e+ + n
detect 0.5 MeV -rays from
e+e–   (t = 0)
neutron “thermalization”
Followed by capture in Cd nuclei
Emission of delayed -rays
(average delay ~30 s)
H2O +
CdCl2
I, II, III:
Liquid scintillator
2 m
Event rate at the Savannah
River nuclear power plant:
3.0  0.2 events / h
in agreement with
expectations

41. Cosmic ray muon stopping decaying to an electron
in a cloud chamber and
decaying to an electron 
decay electron track
±  e± +  + 
Muon decay
Decay electron
momentum distribution
Muon spin = ½
Muon lifetime at rest:  = x s  s
Muon decay mean free path in flight:
p : muon momentum
c  0.66 km
 muons can reach the Earth surface after a path  10 km because
the decay mean free path is stretched by the relativistic time
expansion

42. Lepton Number Conservation
Electron, Muon and Tau Lepton Number
Lepton
Conserved Quantity
Lepton Number e- Le +1 ne m- Lm nm t- Lt nt
Anti-Lepton
Conserved Quantity
Lepton Number e+ Le -1 ne m+ Lm nm t+ Lt nt
We find that Le , Lm and Lt are each conserved quantities

43. Lepton Number Conservation
n  p e ne Le B +1 +1 +1 -1 . .
m  e ne nm Lm Le -1 -1 +1 -1 . .
The first two processes are not forbidden by lepton number conservation, while the third is. Note that we require that both electron number and muon number are conserved. If tau or tau neutrinos were involved, we would also check this as well.
m  e g Lm Le -1 -1 X

44. Other conserved quantities
Baryon Number Conservation
When we collide particles together, we find that the number of baryons is conserved.
A + B  C + D
For each baryon, we simply assign B = +1 (protons, neutrons, for example)
For each anti-baryon ,we assign B = -1 (antiprotons, antineutrons, for example)
 Compute the total baryon number on each side and they must be equal!

45. Baryon number conservation
B = +1 for baryon in a decay or reaction, and B = -1 for each anti-baryon, then the total baryon number must be the same before and after the process.
Eg p+ + n  p+ + p+ + n + p-  .
p+ + n  p+ + p+ + p-  X

46. More and More Mystery particles
Recall: We had many new types of matter!
More and More Mystery particles
Fermilab: Bubble
Chamber Photo

47. Strange particles observed: Long lifetimes & Heavy

48. Invention of a new, additive quantum number “Strangeness” (S)
(Gell-Mann, Nakano, Nishijima, 1953)
conserved in strong interaction
processes:
not conserved in weak decays:
S = +1: K+, K° ; S = –1: , ±, ° ; S = –2 : °, – ;
S = 0 : all other particles
(and opposite strangeness –S
for the corresponding antiparticles)

49. Summary of strangeness puzzles & their contribution to the SM
: Strangeness  quark model
 Basis for QCD
1956: Parity violation
Spin-dependence of weak interactions
1964: Suppression of Flavour Changing NC
 Suggested charm quark
 Properties of the neutral currents
1964: CP violation
 Absolute matter-antimatter asymmetry…

50. Puzzle #1 -- Strange particles observed: Long lifetimes & Heavy
Strangeness
- produced by strong interaction
conserved by strong interactions
 these strange particles produced in pairs d u g s s u u d

51. Invariance under Lorentz transformation implies  CPT invariance
Therefore… big impact on the foundation of the theory, if interactions behave in different ways under:
Charge conjugation(C): reverses the electric charge & all the internal quantum numbers.
Parity (P): space inversion; reversal of the space coordinates.
Time reversal (T): replacing t by -t. This reverses time derivatives like momentum and angular momentum.
 Particles and antiparticles have identical masses and lifetimes. This arises from CPT invariance of physical theories and is used experimentally to test CPT.

52. Kaons are mesons (Spin = 0; Parity = -1):
Puzzle #2 – Parity violating Decays: V-A Theory of Weak Interactions (WI)
Kaons are mesons (Spin = 0; Parity = -1):
K+  p+p P=(-1)(-1) Even
 p+p-p P=(-1)(-1)(-1) Odd
Strangeness not conserved WI
Extra confidence in the V-A theory
(Spin-Flip)
 BR = 63%
Helicity suppressed due to low mass
of e+
 BR = %

53. Extra u like quark needed to
Puzzle #3 – Low rate of KLm+m-: Predicts no mixing with Z0 boson & existence of Charm Quark
Consistent with observed rate ~10-5
If possible should represent ~ 60% of the decays
 Not Observed d s u W- W+ _ m- m+ nm KL d s c W- W+ _ m- m+ nm KL
Flavor Changing
Neutral Current
(FCNC) not allowed
Extra u like quark needed to
get proper rate Charm

54. Puzzle #4 – CP violating Decays (CP): K0 reveals a more intricate picture
Flavor Eigenstate K0 - K0
oscillations d s - W- K0 K0
u, c, t
u, c, t _ _ W+ s d s d
u, c, t - K0 W- _ _ _ W+ _ K0 _
u, c, t s d

55. K0 - K0 Oscillation quantified from leptonic decay
Get positron:
Kaon Interferometry
G+ >> G-
G+ ≈ Dm
Or electron:

56. Puzzle #4 – CP violating Decays (CP): K0 reveals a more intricate picture
Flavor Eigenstate K0 - K0
oscillations
CP Eigenstate d s - W-
K1oo
K1+-
K2+-o
K2ooo K0 K0
u, c, t
u, c, t
CP=+1 _ _ W+ s d s d
u, c, t -
CP=-1 K0 W- _ _ _ W+ _ K0 _
u, c, t s d
Mass Eigenstate  Before observation of CP violation
 = 0.9 x s
 = 5.2 x 10-8 s

57. Why Puzzle #4 was so interesting
Why Puzzle #4 was so interesting? Potential Solution to the Baryon Asymmetry in the Early Universe
 2 g
10,000,000,001
10,000,000,000
 They basically have all annihilated away except a tiny difference between them

58. Baryon Asymmetry in the Current Universeus 1
…This is us TODAY!!!
… After 40 years of studying CP-violation in the quark sector:
Now we know that the effect is too small to be source of the
Baryon Asymmetry

59. THE “STATIC” QUARK MODEL
Late 1950’s – early 1960’s: discovery of many strongly interacting particles
at the high energy proton accelerators (Berkeley Bevatron, BNL AGS, CERN PS),
all with very short mean life times (10–20 – 10–23 s, typical of strong decays)
 catalog of > 100 strongly interacting particles (collectively named “hadrons”)
ARE HADRONS ELEMENTARY PARTICLES?
1964 (Gell-Mann, Zweig): Hadron classification into “families”;
observation that all hadrons could be built from three spin ½
“building blocks” (named “quarks” by Gell-Mann):
u d s
Electric charge
( units |e| )
Baryonic number
Strangeness
+2/ / /3
1/ / /3
and three antiquarks ( u , d , s ) with opposite electric charge
and opposite baryonic number and strangeness

60. The quark model 1964 Gell-Mann, Zweig
there are three quarks and their antiparticles
each quark can carry one of three colors
red blue green
anti-quarks carry anticolor
anti-red anti-blue anti-green
Quark Up
Down
Strange
Charge
+2/3
-1/3

61. The quark model
only colorless (“white”) combinations of quarks and antiquarks can form particles
qqq qq
no others observed

62. SU(3) Flavor Symmetry  uds
1964 Symmetry operations on an octahedron illustrate the theory of quarks. Theorist Murray Gell-Mann (and, independently, Yuval Ne'eman) discovered a theory that organized all the particles into families with properties mathematically the same as those of a "group of eight" in abstract algebra. Gell-Mann called it "The Eightfold Way." When physicists recognized that underlying fundamental particles could explain the eightfold pattern, the idea of quarks was born.
In the 1970s, experiments at the Department of Energy's SLAC showed that quarks were not just mathematical constructs but real building blocks of protons and neutrons.

63. The 8-fold way baryons qqq mesons qq 0 - + + 0  - 0 - ++ -
uss
uus
dss
dds
udd
uud
uds -
ddd
++
uuu -
sss n p
mesons qq K0 - K+ +
0  K- sd ud su du ds us
uu,dd

64. Prediction and discovery of – particle
A success of the static quark model 3 2
The “decuplet” of spin baryons
Strangeness Mass (MeV/c 2 )
D D D° D–
uuu uud udd ddd
– * *° *–
suu sud sdd
– *° *–
ssu ssd
– – (predicted)
sss
W–: the bound state of three s – quarks with the lowest mass
with total angular momentum = 3/ 2 
Pauli’s exclusion principle requires that the three quarks
cannot be identical

65.
ETC…

66. Quark confinement What holds quarks/antiquarks together? strong force
acts between all “colored” objects
short range
independent of distance

67. 1968-1999 J/ (charm) (1974) J.J, Aubert, J.E. Augustin
First major discovery with Solid State Detectors
J/ (charm) (1974) J.J, Aubert, J.E. Augustin
t lepton(1975) M.Perl et al
B-mesons(1981) CLEO
W,Z(1983) UA1
number of n (1991) LEP
t-quark(1994) CDF

68. Conclusion -- Standard Model – Fundamental Particles
Leptons: q=1
q=0 e ne u d m nm c s t nt b
Missing H
Higgs
q=0
Quarks: q=+2/3
q=-1/3
Only one missing Component
Discovery Dates Add?
Force Carriers
q=0
q=0
q=1
q=0