The Development of Particle Physics - vitaly · There will be 4 homeworks contributing a total of 10% each to the final mark ... Modern View (the Standard Model) Particle ... The

The Development of Particle Physics

Dr. Vitaly Kudryavtsev E45, Tel.: 0114 2224531

[email protected]

Dr. Vitaly Kudryavtsev The Development of Particle Physics Lecture 1

Introduction to the course

PHY466: THE DEVELOPMENT OF PARTICLE PHYSICS Dr. Vitaly Kudryavtsev, E45, tel.: 2224531 E-mail: [email protected]

•  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 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.


Learning outcomes

•  On successful completion of the module you should: •  Be familiar with the experimental methods and techniques used

in particle physics experiments, be able to analyse their advantages and compare them with each other.

•  Demonstrate understanding and ability to critically assess crucial particle physics experiments carried out during last 100 years and their results.

•  Understand basic principles of theoretical models and their development, be able to analyse their connection to experimental data.

•  Be confident in communicating scientific results to your peers via oral presentations and essays.


Textbooks

•  Textbooks 1. “The experimental foundations of particle physics” by R. N. Cahn and

G. Goldhaber, published by Cambridge University Press, 2nd edition. 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. 5. Other textbooks on Particle Physics.


Course structure

•  Course structure The course follows Cahn and Goldhaber and will consist of a set of lectures by myself and 15-20-minute presentations by students. Students will form pairs and each pair will be assigned a topic that will be presented in class. 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 discussions. The schedule will be posted on the web after the students are assigned topics for presentations. The students have to choose a topic by Tuesday, 3 October (talk to me).

26,28/09 L1 Introduction. Discovery of the neutron and the positron. 03/10 L2 Discovery of the muon and the pion. 05/10 L3 Discovery of strangeness. 10/10 L4 Resonances.

From 11/10 – talks given by students and lectures by VK.


Assessment

•  No formal exam!

The assessment will consist of three elements: 1.  30% for the presentation. Each presentation will be assessed by two people.

You will be preparing presentations and delivering them in pairs. 2.  There will be 4 homeworks contributing a total of 10% each to the final mark. 3.  There will also be an essay (about 4000 words) amounting to 30% of the final

mark. Each essay will be assessed by two people. Note: The department takes very seriously all cases of plagiarism and collusion.

Please, submit your essays in two hard copies and in the electronic form. The electronic version should be submitted by YOU to Turnitin system first.


Topics for lectures and student presentations

1.  Introduction. Discovery of the neutron and the positron. 2.  Discovery of the muon and the pion. 3.  Strangeness. 4.  Resonances. 5.  Antibaryons: antiprotons. 6.  Antibaryons: antineutrons. 7.  Weak interactions: experimental evidence for neutrino. 8.  Weak interactions: evidence for two neutrinos. 9.  Weak interactions: parity violation. 10.  Kaon system: discovery of the K0

L. 11.  Kaon system: CP violation. 12.  Nucleon structure: ep elastic scattering. 13.  Nucleon structure: ep inelastic scattering 14.  Nucleon structure: νp inelastic scattering.


Topics for lectures and student presentations

15.  New particles: J/ψ. 16.  New particles: charm. 17.  New particles: τ-leptons. 18.  Quarks, gluons and jets: quark jets. 19.  Quarks, gluons and jets: gluon jets. 20.  Quarks, gluons and jets: UA2-experiment. 21.  The fifth quark: discovery of Υ and B-meson. 22.  Neutral currents and weak vector bosons: neutral currents. 23.  Neutral currents and weak vector bosons: W-bosons. 24.  Neutral currents and weak vector bosons: Z -bosons. 25.  Discovery of the top-quark. 26.  Discovery of ντ. 27.  LEP experiments. 28.  Neutrino mass and oscillations.


Some notes on giving presentation

•  Your presentation should last about 15-20 min followed by a ~5 minute question/discussion period.

•  Step 1: Get guidelines from me and generate a draft of your talk (on a 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 prepare your slides using Microsoft PowerPoint and show them from laptop

computer using data projector. If you prepare your talk on Windows, your fonts and pictures may not be seen properly on my Mac. So, please, see me well in advance to check fonts and pictures. You can also use university computers, your own laptop or convert your presentation to pdf (this usually removes problems with the format).

•  You should provide me with a copy of your presentation (preferably electronic copy) and this will be used in marking your presentation. I would like to put your presentations on the web to allow other students to use them in writing essay and answering homework questions.

Some hints on presentations

•  Use colours, bold, italic, to make your presentation visually interesting. •  Do not crowd a slide and make sure your font is visible (14 pt is a small print

on a slide). •  Make sure your figures are clear. •  For 15-20 minutes you will need 10-20 slides. It depends on how fast you go

and how dense your slides are. It is a good idea to go through your talk and time yourself (with your partner).

•  Have a structure of your talk: tell a story beginning, middle and end. •  Do not exceed 20 minutes’ limit. •  Start your presentation with a title and your name; include outline. •  End your presentation with a summary and the list of references (properly

formatted).



Some notes on giving presentation

•  Do not exceed 20 min limit.•  Presentation assessment:

•  Content - 25%•  Clarity - 25%•  Presentation - 25%•  Questions - 25%

•  You should view this as an opportunity to learn how to speak to people in a small informal group.

•  All lectures will be on the web after they are given as part of the course: http://kudryavtsev.staff.shef.ac.uk/phy466/


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.

3. Physics with the ATLAS detector at LHC.The essay should include the description of the LHC and the ATLAS detector, main goals of the ATLAS experiment and the results so far. Search for Higgs bosons and Supersymmetry, and the results should be included.


Hand-in date for essay

•  The guidelines are not explicit and essays should also contain other material relevant to the topic.

•  Essays should be handed into the physics office by 4 p.m. on Wednesday, 13 December 2017. The essays should be around 4000 words in length with appropriate diagrams (about 10 pages but no limit).

References: Perkins, Cahn and Goldhaber, Coughlan and Dodd, other particle physics textbooks, scientific papers in refereed journals.


Introduction. Discovery of the neutron and the positron.

Outline

•  Introduction: Chronology of particle physics.•  Discovery of the neutron.•  Discovery of the positron.


•  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 - 1550 AD: The Ancients

1550 - 1900 : The Scientific Revolution and Classical Mechanics 1900 - 1964 : Quantum Theory 1964 - Present: The Modern View (the Standard Model)

Particle Physics Timeline


Particles discovered 1898 - 1964:


Particles discovered since 1964:

ντ H


Chronology of Particle Physics

1895 Discovery of X-rays (W. Roentgen) 1896 Discovery of radioactivity (H. Becquerel) 1897 Discovery of electron (J.J. Thomson) 1898 Isolation of radium (M. Curie and P. Curie) 1905 Special theory of relativity (A. Einstein) 1909 Alpha particle shown to be helium nucleus (Rutherford and Royds) 1911 Discovery of nucleus (E. Rutherford) 1912 Discovery of cosmic radiation (Victor Hess) 1913 Planetary atomic model (N. Bohr) 1915 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)



1928 Theory of α-radioactivity (Gamow, Gurney, Condon) 1930 Hubble discovers expansion of universe 1930 Neutrino hypothesis (W. Pauli) 1930 Invention of cyclotron (E.O. Lawrence) 1932 Discovery of neutron (Chadwick) 1933 Discovery of positron in cosmic rays (Anderson) 1934 Theory of β-radioactivity (E. Fermi) 1935 Meson hypothesis (Yukawa) 1937 Discovery of muon in cosmic rays (Neddermeyer, Anderson) 1947 Discovery of pion in cosmic rays (Powell) 1947 Discovery of V-particles in cosmic rays (strange meson - kaon) (Rochester and Butler) 1950 Discovery of more V-particles (strange baryon - Λ) (Anderson)



1952 More strange particles (Ξ, Σ) discovered in cosmic rays. 1955 Discovery of antiproton at Bevatron (Chamberlain and Segre) 1956 Discovery of antineutron at Berkeley Bevatron 1956 Experimental detection of neutrino (Reines and Cowan) 1974 Discovery of J/ψ resonance (Charm quark) (Richter and Ting) 1975 Discovery of τ-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 neutrino)

(Homestake, GALLEX, SAGE, Super-K, SNO, …) 2012 Discovery of Higgs boson at the LHC (ATLAS, CMS)


Structure of the atom

Thomson's model: Electron is a universal constituent of matter.Atom consists of many electrons with balancing positive charge.

1909 - 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. 1911 - Rutherford published his analysis of the experiment showing that the atom had a small, charged nucleus.1919 - Rutherford found the first evidence for proton by radiating nitrogen with alpha-particles.1920 - Rutherford proposed the existence of neutron, although physicists continued to speak of the nucleus as having A protons and A-Z electrons.


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 heliumatoms. They observed neutral penetrating radiation that they thought was X-rays.In fact, they observed the reaction:

€

24 He + 4

9Be → 612C + 0

1nCurie and Joliot showed that this radiationwas able to knock protons out ofparaffin. But they misinterpreted thephenomenon as scattering of gamma rayson protons (a process similar to the Compton effect - scattering of gamma rayson electrons).


Discovery of the neutron: Chadwick’s experiment

•  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. 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 recoiling ions of the element.

•  James Chadwick reported to Lord Rutherford on Joliot-Curies' result. •  Lord Rutherford "I do not believe it!"


Discovery of the neutron

•  If the ejection of a proton is due to the scattering of a photon on a nucleus, then to speed up the 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 a mass equal to that of the proton.

•  Chadwick called it the neutron in a letter to Nature in February 17, 1932. •  1935 - Chadwick received the Nobel Prize.


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 typecloud chamber

Original Wilsonchamber


Cloud chamber (Wilson chamber)

Tracks of particles in the cloud chamber

Different types of particles will leave different trails. Alpha particles, which arerelatively 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 isproportional to the radius of 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.


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 were a proton, then its kinetic energy (from the track curvature, which determines its momentum) would be 300 keV and the track length would be 5 mm in air. So the mass of the particle should be close to me.

•  If the mass is known, then the specific ionisation (also in lead) gives the magnitude of the charge.

•  Anderson concluded that the positive charge of the particle is less than twice (or is probably exactly equal to) that of the proton (electron) and the mass is less than 20 me.


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 another particle with matter (not emitted from atom or nucleus).


References

1.  J. Chadwick. "Possible existence of a neutron", Nature, 129, 312 (1932). 2.  C. D. Anderson. "The positive electron", Phys. Rev., 43, 491 (1933).


References

•  High Energy Physics Literature Database: http://inspirehep.net •  The Review of Particle Physics: http://pdg.lbl.gov •  Physical Review home page: http://publish.aps.org •  LANL e-print archives: http://xxx.lanl.gov •  Web of Knowledge: http://wok.mimas.ac.uk •  SCOPUS (papers, preprints etc.): http://www.scopus.com •  Materials from the web-site http://particleadventure.org have been used in

preparation of this lecture.

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The Development of Particle Physics - vitaly · There will be 4 homeworks contributing a total of 10% each to the final mark ... Modern View (the Standard Model) Particle ... The