DOCSLIB.ORG

Very Elementary Particle Physics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Very Elementary Particle Physics 17 Very Elementary Particle Physics Martinus J.G. Veltman Abstract This address was presented by Martinus J.G. Veltman as the Nishina Memorial Lecture at the High Energy Accelerator Research Organization on April 4, 2003, and at the University of Tokyo on April 11, 2003 Introduction Today we believe that everything, matter, radiation, gravita- tional fields, is made up from elementary particles. The ob- ject of particle physics is to study the properties of these el- ementary particles. Knowing all about them in principle im- plies knowing all about everything. That is a long way off, we do not know if our knowledge is complete, and also the way from elementary particles to the very complicated Uni- verse around us is very very difficult. Yet one might think that at least everything can be explained once we know all about the elementary particles. Of course, when we look to Martinus J.G. Veltman such complicated things as living matter, an animal or a hu- c NMF man being, it is really hard to see how one could understand all that. And of course, there may be specific properties of particles that elude the finest detection instruments and are yet crucial to complex systems such as a human being. In the second half of the twentieth century the field of elementary particle physics came into existence and much progress has been made. Since 1948 about 25 Nobel prizes have been given to some 42 physicists working in this field, and this can be seen as a measure of the amount of ingenuity involved and the results achieved. Relatively little of this is known to the general public. Martinus J.G. Veltman (1931 – ). Nobel Laureate in Physics (1999) University of Michigan (USA) at the time of this address M. J. G. Veltman: Very Elementary Particle Physics, Lect. Notes Phys. 746, 371–392 (2008) DOI 10.1007/978-4-431-77056-5 17 c Nishina Memorial Foundation 2008 372 Martinus J.G. Veltman In this short account a most elementary introduction to the subject is presented. Itmaybeasmallsteptohelpbridgingthe gap between the scientific knowledge achieved and the general understanding of the subject. Photons and Electrons Photons are very familiar to us all: all radiation consists of photons. This includes radio waves, visible light (from red to dark blue), X-rays, gamma rays. The first physics Nobel prize, in 1901, was given to R¨ontgen, for his discovery of X-rays or r¨ontgen rays. The 1921 physics Nobel prize was awarded to Einstein for his discovery that light is made up from particles, photons. Einstein is most famous for his theory of relativity, but it is his discovery of photons that is mentioned by the Swedish Academy. Indeed, many think that this is perhaps his most daring and revolutionary discovery! The difference between all these types of photons is their energy. The photons of radio waves have lower energy than those of visible light (of which red light photons are less energetic than blue light photons), those of X-rays are of still higher energy, and the gamma rays contain photons that are even more energetic than those in X-rays. In particle physics experiments the photon energies are usually very high, and then one deals with individual photons. The energy of those photons starts at 100,000,000,000 times that of the photons emitted by portable phones. Fig. 17.1 Especially at lower energies the number of photons involved is staggering. To give an idea: a 1 watt portable phone, when sending, emits roughly 10,000,000,000,000,000,000,000 photons per second. Together these photons make the wave pattern of radio waves. Also in visible light the number of photons is generally very large. Interestingly, there exist devices, called photo-multipliers that are so sensitive that they can detect single photons of visible light. The photons of visible light are one million times as energetic as those emitted by a portable phone, and while the number of photons emitted is correspondingly lower the amount is still enormous. 17 Very Elementary Particle Physics 373 Electrons are all around us. They move in wires in your house, make light, and function in complicated ways in your computer. They also make the pictures on your TV or computer screen. In the tube displaying the picture electrons are accelerated and deflected, to hit the screen thereby emitting light. Fig. 17.2 In the tube, on the left in the picture, a piece of material called the cathode is heated. As a consequence electrons jump out of the material, and if nothing were done they would fall back. However, applying an electric field of several thousand volt they are pulled away and accelerated. Then they are deflected, usually by means of magnetic fields generated by coils, deflection coils. They make the beam of elec- trons move about the screen. There they paint the picture that you can watch if you have nothing better to do. Thus inside your TV tube there is an accelerator, although of rather low energy as accelerators go. The energy of the electrons is expressed in electron-Volts. An electron has an energy of one electron-Volt (abbreviated to eV) after it has been accelerated by an electric field of 1 Volt. In a television tube the field may be some- thing like 5000 V, thus the electrons in the beam, when they hit the screen, have an energy of 5000 eV. In particle physics the energies reached are much higher, and one uses the unit MeV. One MeV is one million eV. Thus the electrons inside the TV tube have an energy of 0.005 MeV. Try to remember that unit, because it is used everywhere in particle physics. Related units are GeV (1GigaeV = 1000MeV) and TeV (1 Tera eV = 1000GeV). 374 Martinus J.G. Veltman Making New Particles In order to make particles one must first make an energetic beam of electrons or protons. Protons can be found in the nucleus of an atom together with neutrons. The simplest nucleus is that of hydrogen, it contains only one proton. The picture shows a hydrogen atom, one proton with one electron circling around it. The electron is negatively charged, the proton has exactly the same charge but of the opposite sign. The total charge of a hydrogen atom is the sum of these two and Is thus zero, it is electrically neutral. Fig. 17.3 The first step then is to take a box filled with hydrogen. Subsequently a strong spark, an electric discharge, is produced in that box. This amounts to a beam of electrons moving through the hydrogen. When it meets a hydrogen atom on its way the electron is knocked out of the atom, and there results an electron and a proton drifting in that box. Ionization is the name given to the process of stripping electrons from an atom. Fig. 17.4 The next step is to apply an electric field. If the field is positive on the left then the electrons are pulled to the left and the protons, having the opposite charge, are pulled to the right. Making a little window (of some thin material) the protons emerge on the right hand side and one has a proton beam. Likewise one has en electron beam on the left hand side, but this is not an efficient way to make electron beams. One can do it better as shown by the TV tube. 17 Very Elementary Particle Physics 375 To produce new particles one must create a minuscule bubble of concentrated energy. From Einstein’s equation E = mc2 we know that matter is a form of energy, and in order to make a particle of some mass one must have an energy bubble of at least that much energy. The bubble will decay into whatever is possible, sometimes this, sometimes that. But always, the energy equivalent to the sum of the masses of the particles that it decays into is less than the initial energy of the bubble. That is why particle physicists want forever bigger accelerators. Those bigger machines create ever more energetic bubbles, and very heavy particles, not seen before, may appear among the decay products of those bubbles. To create a bubble of high energy the beam of protons coming out of the ioniza- tion chamber is accelerated to high energy, and then the protons are smashed into other particles, for example particles in an atomic nucleus. Thus one simply shoots the beam into a suitable material, a target. Whenever there is a collision of a particle in the beam with a nucleus a bubble will form and that bubble will decay into all kinds of particles. In this way new particles can be found. Those particles, themselves little bubbles of energy, are usually unstable and they decay after a little while and that is why they are not seen in the matter around us. There are only a few stable particles, mainly photons, electrons, protons and neutrinos. Fig. 17.5 The new particles found are given names, and their properties are studied. In the early days these particles were called mesons. For example one finds copiously π-mesons, or briefly pions, particles with a mass about 260 times bigger than the electron mass. Those pions decay mostly into a muon (a μ-meson, a particle whose mass is about 200 times that of the electron) and a neutrino (ν, mass 0). The muon, while relatively long-lived, decays in an electron, a neutrino and an anti-neutrino. Anti-particles have almost the same properties as particles (they have the same mass, but opposite charge), but that will be discussed later.
Load more

Recommended publications
  • Lesson 46: Cloud & Bubble Chambers
    Lesson 46: Cloud & Bubble Chambers Imagine you're on a really stupid game show where they put a whole bunch of ping pong balls on the floor, turn off the lights, and then send you in to count them. How would you do it? • I'm thinking that your only chance is to get down on your hands and knees and try to touch them around you. • One of the problems is that in the very act of counting them (by reaching out), you change them by pushing them around, maybe even missing some of them. This is kind of the same problem that subatomic physicists have. They have to reach around “in the dark” to measure something that they can't see. • The amazing part is that methods have been developed to do this, and actually do it accurately. • This is the beginning of our journey into the modern subatomic realm of physics. Cloud Chambers In 1894 the Scottish physicist Charles Wilson was interested in the odd shadows that can sometimes be formed on cloud tops by mountain climbers (called Brocken Spectre). • To be able to study this further, he came up with a way water to build a device called a cloud chamber that would droplets allow him to make his own mini-clouds inside a glass chamber. ◦ To be able to do this he made his device so that he could keep the air inside supersaturated with water. ▪ Air can usually only hold a certain amount of path of vapour. Supersaturated means the air was charged particle holding more vapour than it would normally be Illustration 1: Water droplets condense able to at that pressure and temperature.
    [Show full text]
  • Proton Synchrotron
    PROTON SYNCHROTRON 1. Introduction of the machine. The earliest operational runs were carried out without any of the correcting devices The 25 GeV proton synchrotron has now been being employed, except for the self-powered pole put into operation. Towards the end of November face windings needed to correct eddy currents in 1959 protons were accelerated up to 24 GeV kinetic the metal vacuum chamber at injection when the energy and a few weeks later, after adjustments guiding magnetic field is only 140 gauss. The had been made to the shape of the magnetic field proton beam then disappeared at a magnetic field at field values above 12 OOO gauss by means of pole of about 12 kgauss due to the number of free face windings, the maximum energy was increased oscillations of the particles per revolution becoming to 28 GeV. The intensity of the accelerated beam an integer. As the magnet yoke saturates, the focus­ of protons was measured as 1010 protons per pulse ing forces diminish slightly, and instead of the and there was no noticeable loss of particles during machine working in the stable region between the the whole acceleration period up to the maximum unstable resonance bands, the operating point is energy. slowly forced into a resonance and the particles Measurements so far carried out on the PS are are lost to the walls of the vacuum chamber. In necessarily preliminary and incomplete. It will take later runs the pole face windings were energized by at least six months of measurement work before programmed generators designed to keep the sufficient is known about the behaviour of the ma­ focusing forces constant up to magnetic fields of chine to exploit it as a working nuclear physics tool.
    [Show full text]
  • Mmw11111m1111111111m11111~11~M1111wh CM-P00043015
    CHS-26 '-0 November 1988 N I -VJ CERN LIBRARIES, GENEYA mmw11111m1111111111m11111~11~m1111wH CM-P00043015 STUDIES IN CERN HISTORY The Construction of CERN's First Hydrogen Bubble Chambers Laura Weiss GENEVA 1988 The Study of CERN History is a project financed by Institutions in several CERN Member Countries. This report presents preliminary findings, and is intended for incorporation into a more comprehensive study of CERN's history. It is distributed primarily to historians and scientists to provoke discussion, and no part of ii should be ci1ed or reproduced wi1hout written permission from the author. Comments are welcome and should be sent to: Study Team for CERN History c!o CERN CH-1211 GENEVE 23 Switzerland Copyright Study Team for CERN History, Geneva 1988 CHS-26 November 1988 STUDIES IN CERN HISTORY The Construction of CERN's First Hydrogen Bubble Chambers Laura Weiss GENEVA 1988 The Study of CERN History is a project financed by Institutions in several CERN Member Countries. This report presents preliminary findings, and is intended for incorporation into a more comprehensive study of CERN's history. It is distributed primarily to historians and scientists to provoke discussion, and no part of it should be cited or reproduced without written permission from the author. Comments are welcome and should be sent to: Study Team for CERN History c/oCERN CH-1211GENEVE23 Switzerland " Copyright Study Team for CERN History, Geneva 1988 CERN~ Service d'information scicntifique - 400 - novembre 1988 TABLE OF CONTENTS 8.1 Historical overview
    [Show full text]
  • Bubble Chamber
    1: Bubble Chamber Purpose The purpose of this experiment is to determine the rest mass of the pion (mπ) and the rest mass of the muon (mµ). Introduction Particle physics (a.k.a. high energy physics) is the division of physics which investigates the behavior of particles involved in \high" energy collisions. (\High" here means energies greater than those found in nuclear reactions, i.e., more than 100 MeV=0.1 GeV. The highest energy particle accelerators available today produce collisions with energies of a few million MeV = TeV.) The first \new" particles discovered (circa 1940) by particle physicists were the pion (π) and the muon (µ). In spite of roughly similar masses (near 100 MeV, compare: electron mass = .511 MeV and proton mass = 938 MeV), these two particles have quite different properties. The muon is a relative of the electron (and hence is called a lepton). It comes in particle − + 1 (µ ) and anti-particle (µ ) versions and has spin 2 . Unlike the electron, the muon is unstable. It decays into two neutrinos (ν) and an electron (or positron) after a mean life of 2 10−6 s: × µ+ ν¯ + ν + e+ (1.1) −! µ− ν + ν¯ + e− (1.2) −! The pion belongs to the class of particles called mesons. Unlike leptons, mesons interact with protons and neutrons through an additional force called the strong nuclear force (a.k.a., color force). (Particles that can feel this force are called hadrons.) Unlike leptons, mesons are known to be composite particles: each is made of a quark and an antiquark.
    [Show full text]
  • II~ O Llbd 0026270 3 the Yeiu' 1993 Il A
    1111111~/11'~I~~l~i~l~~ij~I'1~~~II~ o llbD 0026270 3 The yeiU' 1993 il a. b&nner anniveuary ior our understanding of nature: it marks the 10th anniversary of the di.covery of the ca.rriera of the Weak force: the Wand Z particles at CERN, the laboratory near Geneva, Switzerland; the 20th anniversary of the discovery of Weak Neutral Currents in Nature: a Thirty Year the Weak Neutral Currents, and the 30th anniversary of the first revealing but null searches Retrospective· for Weak Neutral Currentl that change the Quark Family! All of these developments have left a profound mark on our study of the most fundamental aspects of nature: "the Elementary Particles and their Forces". These observations helped develop the foundation David B. Cline of the Standard Model of Elementary Particles. This article is a partial cele~ration of this Center for Advanced Accelerator anniversary and an attempt to peer into the future implications and gain a 'perspective 011 Department.! of Phllsia & Astronomy these accomplishment.. A. in the telling of the history of any human accomplishments. University of California Los Angdes it will appear more logical than when it actually occurred. We wiU also describe how .. OS Hilgard Avenue, Los Angeiu, CA 900f"-15"7, USA the intervening yean have taught UI the way in which Neutral Currents contribute to A.trophysic. and the ExplOlion o( Supernova, wiU help in future possible break.throu!1;hs UCLA-PPH0052-8/93 2 -0 in the study of Elementary Particles and possibly even the very nature of life on Earth: the double helix structure of DNA, present in all life forms! It can now be said the there have been three major advances in Physics during the Ab,tract past 100 or so yean.
    [Show full text]
  • Student Worksheet:Bubble Chamber
    STUDENT WORKSHEET: BUBBLE CHAMBER PICTURES Woithe, J., Schmidt, R., Naumann, F. (2018). Student worksheet & solutions: Bubble chamber pictures. CC BY 4.0 A guide to analysing bubble chamber tracks including the following activities: - Activity 1: How does a bubble chamber work? - Activity 2: Electrically charged particles in magnetic fields - Activity 3: Particle identification and properties - Activity 4: Particle transformations - Explanation puzzle pieces – cut out (to print on a separate sheet of paper) - Worksheet solutions for teachers Materials needed: - 1 student worksheet per student - Ruler - Scissors - Glue stick - Pocket calculator Where do the bubble chamber pictures come from? This worksheet is based on images recorded by the 2 m bubble chamber at CERN on 10 August 1972. The bubble chamber was exposed to a beam of protons from CERN’s proton synchrotron PS with a momentum of 24 GeV/c. The magnetic field of 1.7 Tesla is pointing out of the page for all images. This bubble chamber was 2 m long, 60 cm high, and filled with 1150 litres of liquid hydrogen at a temperature of 26 K (-247°C). After its closure, this bubble chamber has been donated to the Deutsche Museum in Munich. The original pictures as well as the pictured with coloured tracks can be found online: https://cds.cern.ch/record/2307419 Main body of the 2 m Bubble Chamber © CERN Activity 1: How does a bubble chamber work? A large cylinder is filled with a liquid at a temperature just below its boiling point. Then, the pressure inside the cylinder is lowered by moving a piston out to increase the chamber volume.
    [Show full text]
  • P INTERACTIONS USING a BUBBLE CHAMBER. By
    A STUDY OF 4 Gev/c % -p INTERACTIONS USING A BUBBLE CHAMBER. by 'LIU YAO SUN A thesis presented for the degree of Doctor of Philosophy of The University of London and for the Diploma of the Imperial College, Department of Physics, Imperial College of Science & Technology, London, S.W.7. =============== June 1963. CONTENTS Page Abstract AS 00 SO 0* ts 1. Preface .• .. .. .. PO 2. Introduction Os 400 OP ** 3. CHAPTER I. Pion Resonances. 1.1'. The Chew-Low Extrapolation Method. 5. 1.2. The Pion-Pion Interaction and the p-particle. 8. 1.3. Other Pion Resonances. 10. CHAPTER II. Contribution of the P -particle to g.-P Scattering. 2.1. One Pion Production. 14. 2.2. Low Energy Elastic Scattering. 16. A PENDIX 2.A. .. 19. APPENDIX 2.B. 27. CHAPTER III. Apyaratus and Experimental Procedure. 3.1. The Hydrogen Bubble Chamber. 33. 3.2. The Pion Beam. 34• 3.3. Method of Scanning. • • 34. 3.4. Measurement of Events. 38. 3.5. Data Processing. 40. 3.6. The Maximum Detectable Momentum. 43. 3.7. Measurement of Beam Momentum and Related Quantities. 45. CHAPTER IV. Interpretation of Events. 4.1. Interpretation of Events by -Pitting Prododure 50 412i Identification of Track by Ionization Measurement. 52 CHAPTER IV. -contd. 4.3. Scanning Efficiency and Cross-sactions 53 CHAPTER V Analysis of Four-prong Events. 111•• 5.1. The Reaction + p p + + 63. (A) Angular and Momentum Distributions. (B) Productional channels. (C) The 3 -particle channel. (D) The charged 3/2, 3/2 Isobar channel. (E) The Direct Channel. 5.2.
    [Show full text]
  • Bubble Chamber Experiments for Strong Interaction Studies Kasuke
    203 Bubble Chamber Experiments for Strong Interaction Studies Kasuke TAKAHASHI DK National Laboratory for High Energy Physics Oho-machi, Ts ukub a-gun , Ibaraki 204 Bubble Chamber Experiments for Strong Interaction Studies Kasuke Takahashi KEK (National Laboratory for High Energy Physics) 1. Introductory remarks In my lecture at this summer school, I would like to talk about what we call as "Bubble Chamber Experiment". Though there have been many interesting experiments done for so-called Weak Interaction Studies, I would like to confine myself only tD/the topics of strong interaction studies by using a bubble chamber. Because of the limitation of time I have to leave the topics of bubble chamber technologies out of my talk. Accordingly we will not discuss anything, unless otherwise necessary, about for examples such questions as "what is a bubble chamber ?" or "what should we prepare for bubble chamber exposures, about incident beams, bubble chamber operating condi­ tions, films and so on?" Instead we simply assume that we use a very conventional hydrogen bubble chamber with a size of up to 2-meters, with a usual 20 K Gauss magnetic field. We shall start with questions "What can we see on bubble chamber films ?" and "What can we learn about Strong Interaction Physics from the events we see on the hydrogen bubble chamber films ?" It would be however very helpful for you to know how scanning and measurement of bubble chamber films go, and to understand how measured data are processed into physically interesting results. Scanning; Scanning is to find an event with a specific topologie or some specific topologies in'which we are interested.
    [Show full text]
  • Four Decades of Computing in Subnuclear Physics – from Bubble Chamber to Lhca
    Four Decades of Computing in Subnuclear Physics – from Bubble Chamber to LHCa Jürgen Knobloch/CERN February 11, 2013 Abstract This manuscript addresses selected aspects of computing for the reconstruction and simulation of particle interactions in subnuclear physics. Based on personal experience with experiments at DESY and at CERN, I cover the evolution of computing hardware and software from the era of track chambers where interactions were recorded on photographic film up to the LHC experiments with their multi-million electronic channels. Introduction Since 1968, when I had the privilege to start contributing to experimental subnuclear physics, technology has evolved at a spectacular pace. Not only in experimental physics but also in most other areas of technology such as communication, entertainment and photography the world has changed from analogue systems to digital electronics. Until the invention of the multi-wire proportional chamber (MWPC) by Georges Charpak in 1968, tracks in particle detectors such as cloud chambers, bubble chambers, spark chambers, and streamer chambers were mostly recorded on photographic film. In many cases more than one camera was used to allow for stereoscopic reconstruction in space and the detectors were placed in a magnetic field to measure the charge and momentum of the particles. With the advent of digital computers, points of the tracks on film in the different views were measured, digitized and fed to software for geometrical reconstruction of the particle trajectories in space. This was followed by a kinematical analysis providing the hypothesis (or the probabilities of several possible hypotheses) of particle type assignment and thereby completely reconstructing the observed physics process.
    [Show full text]
  • 5.7 Bubble Chambers at the SPS: a Technique at Its Apogee Horst Wenninger
    164 N. Doble et al. 5.7 Bubble Chambers at the SPS: A Technique at its Apogee Horst Wenninger The story goes that in 1953 Donald Glaser observed bubble forming in his beer glass triggering him to study bubble formation in liquids traversed by cosmic rays. Glaser himself confirmed this during the discussion session of the last International Bubble Chamber Conference, at CERN in July 1993. The era of bubble chambers at CERN lasted 30 years, and finished in 1984 with the closure of BEBC — the Big European Bubble Chamber — and of GARGAMELLE — the large French heavy liquid bubble chamber, famous for the discovery by the neutrino physics collaboration of so‐called neutral current interactions, in striking support of the emerging theory of electroweak interactions. Analysis of data from experiments with bubble chambers in Europe ended ten years later with the conference cited above. Bubble chambers reveal the trajectories of charged particle as they pass through a superheated liquid (Fig. 5.17). A string of gas bubbles produced along the path of ionizing particles form tracks that can be recorded on stereo view photographs. A magnet creating a uniform field allows to determine the momentum of particles by measuring the curvature of the tracks (Fig. 5.18). Direct visible evidence of particle interaction patterns on millions of photos were thus analysed in physics institutes around the world [35]. Technology Meets Research Downloaded from www.worldscientific.com by GERMAN ELECTRON SYNCHROTRON @ HAMBURG on 05/10/17. For personal use only. Fig. 5.17. Schematic showing the principle of bubble chamber operation.
    [Show full text]
  • How to Discern a Physical Effect from Background Noise: the Discovery of Weak Neutral Currents
    How to Discern a Physical Effect from Background Noise: The Discovery of Weak Neutral Currents Samuel Schindler Department of Philosophy Division of History and Philosophy of Science University of Leeds Woodhouse Lane Leeds, LS2 9JT, UK [email protected] ****************************************************************************** Under Review! Please do not cite without permission! ****************************************************************************** Abstract In this paper I try to shed some light on how one discerns a physical effect or phenomenon from experimental background ‘noise’. To this end I revisit the discovery of Weak Neutral Currents (WNC), which has been right at the centre of discussion of some of the most influential available literature on this issue. Bogen and Woodward (1988) have claimed that the phenomenon of WNC was inferred from the data without higher level physical theory explaining this phenomenon (here: the Weinberg-Salam model of electroweak interactions) being involved in this process. Mayo (1994, 1996), in a similar vein, holds that the discovery of WNC was made on the basis of some piecemeal statistical techniques—again without the Salam-Weinberg model (predicting and explaining WNC) being involved in the process. Both Bogen & Woodward and Mayo have tried to back up their claims by referring to the historical work about the discovery of WNC by Galison (1983, 1987). Galison’s presentation of the historical facts, which can be described as realist, has however been challenged by Pickering (1984, 1988, 1989), who has drawn sociological-relativist conclusions from this historical case. Pickering’s conclusions, in turn, have recently come under attack by Miller and Bullock (1994), who delivered a defence of Galison’s realist account.
    [Show full text]
  • How to Spot Subatomic Particles
    Physics | TEACH CERN Artistically enhanced image of particle tracks in a bubble chamber Track inspection: how to spot subatomic particles Identify tracks of subatomic particles from their ‘signatures’ in bubble chamber photos – a key 20th century technology for studying particle physics. By Julia Woithe, Rebecca Schmidt and Floria Naumann What is the Universe made of? What holds it together? How will it evolve? Particle physicists are fascinated by these big eternal questions. By studying elementary particles and their fundamental interactions, they try to identify the puzzle pieces of the Universe and find out how to put them together. Our current understanding is summarised in the Standard Model of particle physics, one of the most successful theories in physicsw1. 40 I Issue 46 : Spring 2019 I Science in School I www.scienceinschool.org TEACH | Physics But how do we know anything about these particles, all of which are much smaller than the atom? From the 1920s Subatomic particles to the 1950s, the primary technique used by particle physicists to observe Ages 16–19 and identify elementary particles was the cloud chamber (Woithe, 2016). This article provides the opportunity to use photographs produced by a By revealing the tracks of electrically bubble chamber at CERN in 1972 to analyse particle tracks and get to charged subatomic particles through a know the typical characteristics of these subatomic particles. supercooled gas, with cameras used to The tasks are inspiring and detailed, and they allow for self- or peer- capture the events, researchers could assessment to be used. The historical aspects of the topic as well as the work out the particles’ mass, electric images could appeal to science teachers running science clubs.
    [Show full text]