1. The Development of Particle Physics
Dr. Vitaly Kudryavtsev
D36a, Tel.:

2. Introduction to the course
PHY466: THE DEVELOPMENT OF PARTICLE PHYSICS
Dr. Vitaly Kudryavtsev, D36a, tel.:
Introduction
The course describes the development of several crucial concepts in particle
physics, emphasising the role and significance of experiments. Students are
encouraged to work from the original literature (the recommended text includes
reprints of key papers). The course will focus not only on the particle physics
issues involved, but also on research methodology - the design of experiments,
the critical interpretation of data, the role of theory, etc. Topics covered
include the discoveries of the neutron, the positron and the neutrino,
experimental evidence for quarks and gluons, the neutral kaon system and
CP violation, etc.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

3. The Development of Particle Physics
Textbooks
Textbooks
1. “The experimental foundations of particle physics” by R. N. Cahn and
G. Goldhaber, published by Cambridge University Press.
2. “Introduction to high energy physics” by D. H. Perkins, published by
Addison-Wesley.
3. “The ideas of particle physics” by G. D. Coughlan and J. E. Dodd, published
by Cambridge University Press.
4. “Particle physics” by B. R. Martin and G. Shaw, published by John Wiley & Sons.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

4. The Development of Particle Physics
Course structure
Course structure
The course follows Cahn and Goldhaber and will consist of a set of lectures by myself and minute presentations by students. Every student will be assigned a topic. Each student should give two presentations (one presentation in the first half and amother one in the second half of the course). The presentation should consist of an introduction to the knowledge of the time, discuss experiments and their results and describe the impact of the results. Presentations will be followed by questions and short discussion. The schedule will be posted on the web when the students will be assigned topics for presentations. The students have to choose a topic by Monday, 4th October (talk to me).
27/09 L1 Introduction. Discovery of the neutron and the positron.
01/10 L2 Discovery of the muon and the pion.
04/10 L3 Discovery of strangeness.
08/10 L4 Resonances.
11/10 – 13/12 Talks given by students and lectures by VK.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

5. The Development of Particle Physics
Assessment
No formal exam!
The assessment will consist of three elements:
20% of the final mark for each of the presentation, making this a total of 40%. Each presentation will be assessed by two people.
There will be two homeworks contributing a total of 20% each to the final mark.
There will also be a word essay amounting to 20% of the final mark. Each essay will be assessed by two people.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

6. Topics for lectures and student presentations
1. Antibaryons: antiprotons.
2. Antibaryons: antineutrons.
Weak interactions: parity violation.
Weak interactions: experimental evidence for neutrino.
Weak interactions: evidence for two neutrinos.
Kaon system: discovery of the K0L.
Kaon system: CP violation.
Nucleon structure: ep elastic scattering.
Nucleon structure: ep inelastic scattering
10. Nucleon structure: p inelastic scattering.
11. New particles: J/.
12. New particles: -leptons.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

7. Topics for lectures and student presentations
13. New particles: charm.
14. Quarks, gluons and jets: quark jets.
15. Quarks, gluons and jets: gluon jets.
16. Quarks, gluons and jets: UA2-experiment.
17. The fifth quark: discovery of .
18. The fifth quark: discovery of B-meson.
19. Neutral currents and weak vector bosons: neutral currents.
20. Neutral currents and weak vector bosons: charged weak vector bosons.
21. Neutral currents and weak vector bosons: Z -bosons.
22. Search for neutrino mass and oscillations.
23. Solar neutrinos.
24. Discovery of the t-quark.
25. Discovery of .
26. Present and future of particle physics and particle astrophysics
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

8. Some notes on giving presentation
Your presentation should last about min followed by a 5-minute question/discussion period.
Step 1: Generate a draft of your talk (on a plain paper or computer).
Step 2: Talk to me, we will go through your talk and check that you have made the essential points. This should be done well in advance.
Step 3: Revise your talk.
You can get transparencies and pens from the departmental office. You can also prepare your slides using the Microsoft PowerPoint and show them from laptop computer using LCD projector (see me if you want to do this). If you prepare your talk on Windows, your fonts may not be seen properly on my Mac. So, please, see me well in advance to check fonts.
You should provide me with a copy of your presentation (hard copy or electronic copy) and this will be used in marking your presentation. Ideally I would like to put your presentations on the web to allow other students to use them in writing essay and answering homework questions.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

9. Some notes on giving presentation
You should view this as opportunity to learn how to speak to people in a small informal group.
All lectures will be on the web after there were given as part of the course.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

10. The Development of Particle Physics
Topics for essays
Choose one of the following:
1. Development of the theory of electroweak interactions.
This essay should present a review of experimental evidence that has led to the development of the current electroweak theory. Parity violation, discovery of neutrino, demonstration of two distinct neutrinos and the discovery of the neutral currents should be included. The essay should also contain the basic principles, the development and the current status of the electroweak theory.
2. Development of the theory of strong interactions.
This should present a review of quarks and gluons, parton model and structure functions. The essay should also include the discovery of jets, evidences for quark colors, hypothesis of scaling and scaling violation.
Essays should be handed into the physics office by 5 p.m. on Monday, 13 December The essays should be around words in length with appropriate diagrams (about 10 pages).
References: Perkins, Cahn and Golhaber, Coughlan and Dodd, other particle physics textbooks, scientific journals.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

11. Introduction. Discovery of neutron and positron.
Outline
Introduction: Chronology of particle physics.
Discovery of neutron.
Discovery of positron.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

12. Particle Physics Timeline
For over two thousands years people have thought about fundamental particles from which all matter is made, starting with the gradual development of atomic theory, followed by a deeper understanding of the quantized atom, leading to the recent theory of the Standard Model.
Earliest times AD: The Ancients
: The Scientific Revolution and Classical Mechanics
: Quantum Theory
Present: The Modern View (the Standard Model)
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

13. Particles discovered 1898 - 1964:
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

14. Particles discovered since 1964:
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

15. Chronology of Particle Physics
Discovery of X-rays (W. Roentgen)
Discovery of radioactivity (H. Becquerel)
Discovery of electron (J.J. Thomson)
1898 Isolation of radium (M. Curie and P. Curie)
Special theory of relativity (A. Einstein)
1909 Alpha particle shown to be helium nucleus (Rutherford and Royds)
Discovery of nucleus (E. Rutherford)
Discovery of cosmic radiation (Victor Hess)
Planetary atomic model (N. Bohr)
General theory of relativity (final form) (A. Einstein)
1919 Eddington observes deflection of light by Sun in total eclipse
1926 Quantum mechanics (E. Schrodinger)
1927 Dirac equation and prediction of antiparticles (P. Dirac)
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

16. Chronology of Particle Physics
Theory of - radioactivity (Gamow, Gurney, Condon)
Hubble discovers expansion of universe
Neutrino hypothesis (W. Pauli)
Invention of cyclotron (E.O. Lawrence)
Discovery of positron in cosmic rays (Anderson)
Discovery of neutron (Chadwick)
Theory of -radioactivity (E. Fermi)
Meson hypothesis (Yukawa)
Discovery of muon in cosmic rays (Neddermeyer, Anderson)
Discovery of pion in cosmic rays (Powell)
Discovery of V-particles in cosmic rays (strange meson - kaon)
(Rochester and Butler)
Discovery of more V-particles (strange baryon - ) (Anderson)
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

17. Chronology of Particle Physics
1952 More strange particles (, ) discovered in cosmic rays.
1955 Discovery of antiproton at Berkeley Bevatron (Chamberlain and
Segre)
1956 Discovery of antineutron at Berkeley Bevatron
1956 Experimental detection of neutrino (Reines and Cowan)
1974 Discovery of J/ resonance (Charm quark) (Richter and Ting)
1975 Discovery of -lepton (Perl)
1977 Discovery of Bottom quark
1983 Discovery of W and Z bosons (Rubbia and Van der Meer)
1995 Discovery of Top quark (D0 and CDF)
2000 Discovery of tau-neutrino (DONUT)
1995- Discovery of neutrino mass and oscillations (solar and atmospheric
2001 neutrino) (Homestake, GALLEX, SAGE, Super-K, SNO)
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

18. The Development of Particle Physics
Structure of the atom
Thomson's model:
Electron is a universal constituent of matter.
Atom consists of many electrons with balancing positive charge.
Geiger, Marsden and Rutherford: scattering of alpha particles off thin
metal foil. Many of the alpha particles were scattered through large angles,
in disagreement with Thomson model of atom.
Rutherford published his analysis of the experiment showing that the atom
had a small, charged nucleus.
Rutherford found the first evidence for proton by radiating nitrogen with
alpha-particles.
Rutherford proposed the existence of neutron, although physicists
continued to speak of the nucleus as having A protons and A-Z electrons.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

19. Discovery of the neutron
Bothe and Becker, and Curie and Joliot (1931) - experiment which involves
irradiation of beryllium by alpha particles from polonium source. At that time
alpha particles were already known (Rutherford) to be doubly ionised helium
atoms. They observed neutral penetrating radiation that they thought was X-rays.
In fact, they observed the reaction:
Curie and Joliot showed that this radiation
was able to knock protons out of
paraffin. But they misinterpreted the
phenomenon as scattering of gamma rays
on protons (a process similar to the
Compton effect - scattering of gamma rays
on electrons).
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

20. Discovery of the neutron: Chadwick’s experiment
James Chadwick reported to Lord Rutherford on Joliot-Curies' result.
Lord Rutherford "I do not believe it!"
Chadwick used ionisation chamber in which he could measure ionisation (number
of ions) produced by a charged particle and the length of the track. He also used
alpha particles from polonium source and beryllium as a target for alpha particles.
He put several additional target materials (hydrogen, helium, lithium, beryllium,
carbon, air and argon) on the way of neutral radiation from beryllium.
Particles ejected from hydrogen behaved like protons (what else can we expect to
be ejected from hydrogen?) with speeds up to 3.2109 cm/s. The particles ejected
from heavier targets had larger ionising power and were in each case recoil ions
of the element.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

21. Discovery of the neutron
If the ejection of a proton is due to the scattering of photon on nucleus, then to
speed up proton up to 3.2109 cm/s, a 52 MeV photon is needed. This exceeded
all known energies of photons, emitted by nuclei.
Similar process on nitrogen with 52 MeV photons would produce 400 keV
nitrogen recoils with ionisation yield and track length much less than observed
in Chadwick’s experiment.
All difficulties disappear if we assume that incident particles are neutral particles
with the mass equal to that of proton.
Chadwick called it the neutron in a letter to Nature in February 17, 1932.
Chadwick received the Nobel Prize.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

22. Discovery of the positron
Search for new fundamental particles by C. D. Anderson (since 1933).
X-rays and radioactive sources have limited energies (up to a few MeV).
Higher energies were reachable using cosmic rays.
Pioneering measurements of cosmic rays were done by Victor Hess and Dmitry
Skobeltzyn.
A cloud chamber (Wilson chamber) was normally used at that time to detect
tracks of charged particles. It contained a supersaturated vapour. When a charged
particle enters the chamber, it collides with air or alcohol vapour atoms,
producing free ions (ionisation process). Vapour in the chamber condenses
around these free ions, forming droplets. The droplets are what form the trail.
Expansion type
cloud chamber
Original Wilson
chamber
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

23. Cloud chamber (Wilson chamber)
Tracks of particles in
the cloud chamber
Different types of particles will leave different trails. Alpha particles, which are
relatively heavy, will produce straight dense trails (left). Slow electrons leave
wispy, irregular trails (centre). Tracks of cosmic-ray particles are shown on the
right.
Particle track can be photographed. Cloud chamber can be placed in a magnetic
field, thus allowing the measurement of the particle momentum which is inversely
proportional to the curvature of the track in the magnetic field. Particle momentum
component perpendicular to the field is p(MeV/c)=0.310-3 B(gauss) r(cm), where
r is the radius of curvature.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

24. Discovery of the positron
Anderson used cloud chamber in a 15 kG magnetic field.
The chamber was divided into two parts by a 6-mm lead plate.
Greater curvature of the track in the upper part of the chamber indicates that the particle entered the chamber from below. This determines the positive charge of the particle.
If this was a proton, then its energy (from the track curvature, which determines its momentum) would be eV and the track length would be 5 mm in air. So the mass of the particle should be similar to the electron mass.
If the mass is approximately known, then specific ionisation (including the energy loss in lead) gives the magnitude of the charge of the particle.
Anderson concluded that the positive charge of the particle is less than twice (or is probably exactly equal to) that of proton (electron) and the mass is less than twenty times the electron mass.
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

25. The Development of Particle Physics
Summary
The atom was completed in 1932 with the discovery of neutron.
The positron, discovered in 1933, was just the first known particle created in an interaction of other particle with matter (not emitted from atom or nucleus).
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

26. The Development of Particle Physics
References
J. Chadwick. "Possible existence of a neutron", Nature, 129, 312 (1932).
C. D. Anderson. "The positive electron", Phys. Rev., 43, 491 (1933).
Dr. Vitaly Kudryavtsev
The Development of Particle Physics

27. The Development of Particle Physics
References
Physical Review home page:
LANL e-print archives: or
CERN e-print archive:
SLAC e-print database:
Web of Science:
Materials from the web-site have been used in preparation of this lecture
Dr. Vitaly Kudryavtsev
The Development of Particle Physics