1. From electrons to quarks –- 1st part: the development of Particle Physics
What is particle physics -- why do it?
Early days – atoms, electron, proton
Models of the atom – Thomson, Rutherford, Bohr
Cosmic rays
Detectors – scintillators, cloud chamber, emulsion, bubble chamber, spark chamber
More particles: neutron, positron
Muon, pion
Kaon – “strange particles”
Webpages of interest
(Fermilab homepage)
(has links to many particle physics sites)
(Fermilab particle physics tour)
(Lawrence Berkeley Lab.)
(CERN -- European Laboratory for Particle Physics)
Outline:

2. What is particle physics?
particle physics or high energy physics
is looking for the smallest constituents of matter (the “ultimate building blocks”) and for the fundamental forces between them;
aim is to find description in terms of the smallest number of particles and forces (“interactions”)
at given length scale, it is useful to describe matter in terms of specific set of constituents which can be treated as fundamental; at shorter length scale, these fundamental constituents may turn out to consist of smaller parts (be “composite”)
concept of “smallest building block” changes in time:
in 19th century, atoms were considered smallest building blocks,
early 20th century research: electrons, protons, neutrons;
now evidence that nucleons have substructure - quarks;
going down the size ladder: atoms -- nuclei -- nucleons -- quarks – preons, strings ???... ???

3. WHY CAN'T WE SEE ATOMS? “seeing an object”
= detecting light that has been reflected off the object's surface
light = electromagnetic wave;
“visible light”= those electromagnetic waves that our eyes can detect
“wavelength” of e.m. wave (distance between two successive crests) determines “color” of light
wave hardly influenced by object if size of object is much smaller than wavelength
wavelength of visible light: between 410-7 m (violet) and 7 10-7 m (red);
diameter of atoms: m
generalize meaning of seeing:
seeing is to detect effect due to the presence of an object
quantum theory  “particle waves”, with wavelength 1/(m v)
use accelerated (charged) particles as probe, can “tune” wavelength by choosing mass m and changing velocity v
this method is used in electron microscope, as well as in “scattering experiments” in nuclear and particle physics

4. Experimental High Energy Physics
Goal:
To understand matter and energy under extreme conditions: at T ~ 1015 K
Why?
To understand more organized forms of matter
To understand the origin and destiny of the universe.
Basic questions:
Are there irreducible building blocks?
Are there few or infinitely many?
What are they?
What are their properties?
What is mass?
What is charge?
What is flavor?
How do the building blocks interact?
Why are there 3 forces?
gravity, electroweak, strong
(or are there more?)

5. 1869: Johann Hittorf (1824-1914) (Münster)
determined that discharge in a vacuum tube was accomplished by the emission of rays ( named “glow rays” by him, later termed “cathode rays”) capable of casting a shadow of an opaque body on the wall of the tube.
rays seemed to travel in straight lines and produce a fluorescent glow where they passed through the glass.
Rays deflected by magnetic field
1870’s: William Crookes ( ) (London):
detailed investigation of discharges;
Confirms Hittorf’s findings about deflection in magnetic field
Concludes that rays consist of particles carrying negative charge
: Heinrich Hertz ( ) (Karlsruhe)
Built apparatus to generate and detect electromagnetic waves predicted by Maxwell’s theory
High voltage induction coil to cause spark discharge between two pieces of brass; once spark forms conducting path between two brass conductors  charge oscillated back and forth, emitting e.m. radiation
Circular copper wire with spark gap used as receiver; presence of oscillating charge in receiver signaled by spark across the spark gap
Experiment successful –
detected radiation up to 50 ft away
Established that radiation had properties reminiscent of light: was reflected and refracted as expected, could be polarized, speed = speed of light

6. 1887: Heinrich Hertz:
Unexpected new observation: when receiver spark gap is shielded from light of transmitter spark, the maximum spark-length became smaller
Further investigation showed:
Glass effectively shielded the spark
Quartz did not
Use of quartz prism to break up light into wavelength components  find that wavelenght which makes little spark more powerful was in the UV
Hertz’ conclusion: “I confine myself at present to communicating the results obtained, without attempting any theory respecting the manner in which the observed phenomena are brought about”

7. 1888: Wilhelm Hallwachs (1859-1922) (Dresden)
Performs experiment to elucidate effect observed by Hertz:
Clean circular plate of Zn mounted on insulating stand; plate connected by wire to gold leaf electroscope
Electroscope charged with negative charge – stays charged for a while; but if Zn plate illuminated with UV light, electroscope loses charge quickly
Electroscope charged with positive charge:
UV light has no influence on speed of charge leakage.
But still no explanation
Calls effect “lichtelektrische Entladung” (light-electric discharge)

8. 1894: Hertz and Philipp Lenard (1862-1947):
Further investigations of cathode rays using discharge tubes:
Cathode rays penetrate through thin Al window ate end of tube,
Cause fluorescence over distance of few centimeters in air
Deflected by magnetic field
No deflection by electric fields
(later explained due to insufficiently good vacuum)
1895: Wilhelm Röntgen ( ) (Würzburg)
Uses discharge tubes designed by Hittorf and Lenard (but improved pump) to verify Hertz’ and Lenard’s experiments
Discovers X-rays -- forget about cathode rays!

9. Röntgen and X-rays: Hand of Anna Röntgen
From Life magazine,6 April 1896

10. 1895: Jean Perrin (1870-1942) (Paris):
Modifies cathode ray tube – adds “Faraday cup” which is connected to electrometer
Shows that cathode rays carry negative charge
1896: Hendrik A Lorentz ( ) (Leiden)
Formulates atomistic interpretation of Maxwell’s equations in terms of electrically charged particles (called “ions” by him)
“Lorentz force” = force exerted by magnetic field on moving charged particles
1896: Pieter A. Zeeman ( ) (Amsterdam)
Observes broadening of Na D line in magnetic field
measures broadening vs field strength
1896: Explanation of this effect by Lorentz:
based on light emitted by “ions” orbiting within Na atom
Calculates expected broadening f  (e/m)B
By comparing with measured line broadening, obtains estimate of e/m of “ions” in Na atom:
e/m  107 emu/g  1011 C/kg (cf modern value of 1.76x10 C11/kg)
1897: three experiments measuring e/m, all with improved vacuum:
Emil Wiechert ( ) (Königsberg)
Measures e/m – value similar to that obtained by Lorentz
Assuming value for charge = that of H ion, concludes that “charge carrying entity is about 2000 times smaller than H atom”
Cathode rays part of atom?
Study was his PhD thesis, published in obscure journal – largely ignored
Walther Kaufmann ( ) (Berlin)
Obtains similar value for e/m, points out discrepancy, but no explanation
J. J. Thomson

11. 1897: Joseph John Thomson (1856-1940) (Cambridge)
Improves on tube built by Perrin with Faraday cup to verify Perrin’s result of negative charge
Conclude that cathode rays are negatively charged “corpuscles”
Then designs other tube with electric deflection plates inside tube, for e/m measurement
Result for e/m in agreement with that obtained by Lorentz, Wiechert, Kaufmann, Wien
Bold conclusion: “we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter... is of one and the same kind; this matter being the substance from which all the chemical elements are built up.“

14. 1899: J.J. Thomson: studies of photoelectric effect:
Modifies cathode ray tube: make metal surface to be exposed to light the cathode in a cathode ray tube
Finds that particles emitted due to light are the same as cathode rays (same e/m)
1902: Philipp Lenard
Studies of photoelectric effect
Measured variation of energy of emitted photoelectrons with light intensity
Use retarding potential to measure energy of ejected electrons: photo-current stops when retarding potential reaches Vstop
Surprises:
Vstop does not depend on light intensity
energy of electrons does depend on color (frequency) of light

17. 1905: Albert Einstein (1879-1955) (Bern)
Gives explanation of observation relating to photoelectric effect:
Assume that incoming radiation consists of “light quanta” of energy hf (h = Planck’s constant, f=frequency)
 electrons will leave surface of metal with energy
E = hf – W W = “work function” = energy necessary to get electron out of the metal
When cranking up retarding voltage until current stops, the highest energy electrons must have had energy eVstop on leaving the cathode
Therefore eVstop = hf – W
 Minimum light frequency for a given metal, that for which quantum of energy is equal to work function
1906 – 1916 Robert Millikan ( ) (Chicago)
Did not accept Einstein’s explanation
Tried to disprove it by precise measurements
Result: confirmation of Einstein’s theory,
measurement of h with 0.5% precision
1923: Arthur Compton ( )(St.Louis):
Observes scattering of X-rays on electrons

18. WHAT IS INSIDE AN ATOM? THOMSON'S MODEL OF ATOM
(“RAISIN CAKE MODEL”):
atom = sphere of positive charge (diameter 10-10 m),
with electrons embedded in it, evenly distributed (like raisins in cake)
Geiger & Marsden’s SCATTERING EXPERIMENT:
(Geiger, Marsden, ) (interpreted by Rutherford, 1911)
get particles from radioactive source
make “beam” of particles using “collimators” (lead plates with holes in them, holes aligned in straight line)
bombard foils of gold, silver, copper with beam
measure scattering angles of particles with scintillating screen (ZnS) .

19. Geiger, Marsden, Rutherford expt.
result:
most particles only slightly deflected (i.e. by small angles), but some by large angles - even backward
measured angular distribution of scattered particles did not agree with expectations from Thomson model (only small angles expected),
but did agree with that expected from scattering on small, dense positively charged nucleus with diameter < m, surrounded by electrons at 10-10 m

21. Rutherford model RUTHERFORD MODEL OF ATOM: (“planetary model of atom”)
positive charge concentrated in nucleus (<10-14 m);
negative electrons in orbit around nucleus at distance 10-10 m;
electrons bound to nucleus by Coulomb force.
problem with Rutherford atom:
electron in orbit around nucleus is accelerated (centripetal acceleration to change direction of velocity);
according to theory of electromagnetism (Maxwell's equations), accelerated electron emits electromagnetic radiation (frequency = revolution frequency);
electron loses energy by radiation  orbit decays,
changing revolution frequency  continuous emission spectrum (no line spectra), and atoms would be unstable (lifetime  s )
 we would not exist to think about this!!

22. Beta decay b decay n ® p + e- + ne _
b decay changes a neutron into a proton
Only observed the electron and the recoiling nucleus
“non-conservation” of energy
Pauli predicted a light, neutral, feebly interacting particle (1930)
the neutrino
Although accepted since it “fit” so well, not actually observed initiating interactions until (Cowan and Reines)
b decay n ® p + e- + ne _

23. g e+ e-

24. Cloud chamber:
Container filled with gas (e.g. air), plus vapor close to its dew point (saturated)
Passage of charged particle  ionization;
Ions form seeds for condensation  condensation takes place along path of particle  path of particle becomes visible as chain of droplets

25. Positron Positron (anti-electron)
Predicted by Dirac (1928) -- needed for relativistic quantum mechanics
Anderson + Neddermeyer discovered it (1932) in a cloud chamber
existence of antiparticles doubled the number of known particles!!!
Positron track going upward through lead plate

27. Experimentalists ... KL ® m-m+ Not seen, but should be common
Strange quark
kaons discovered 1947
KL ® m-m+
Not seen, but should be common
K0 production and decay
in a bubble chamber

28. Experimental High Energy Physics
Method
Subject matter to extreme temperatures and densities.
Energy ~ 2 trillion eV
Temperature ~ 24,000 trillion K
Density ~ 2000 x nuclear density
Accelerate sub-atomic particles, to closer than 100 millionth the speed of light, and arrange for them to collide head on.
Study the debris of particles that emerges from the collisions.

29. Particle physics experiments
collide particles to
produce new particles
reveal their internal structure and laws of their interactions by observing regularities, measuring cross sections,...
colliding particles need to have high energy
to make objects of large mass
to resolve structure at small distances
to study structure of small objects:
need probe with short wavelength: use particles with high momentum to get short wavelength
remember de Broglie wavelength of a particle  = h/p
in particle physics, mass-energy equivalence plays an important role; in collisions, kinetic energy converted into mass energy;
relation between kinetic energy K, total energy E and momentum p : E = K + mc2 = (pc)2 + (mc2)c2
___________

30. About Units Energy - electron-volt mass - eV/c2 momentum - eV/c:
1 electron-volt = kinetic energy of an electron when moving through potential difference of 1 Volt;
1 eV = 1.6 × Joules = 2.1 × W•s
1 kW•hr = 3.6 × 106 Joules = 2.25 × 1025 eV
mass - eV/c2
1 eV/c2 = × kg
electron mass = MeV/c2
proton mass = MeV/c2
professor’s mass (80 kg)  4.5 × 1037 eV/c2
momentum - eV/c:
1 eV/c = 5.3 × kg m/s
momentum of baseball at 80 mi/hr  5.29 kgm/s  9.9 × 1027 eV/c

31. How to do a particle physics experiment
Outline of experiment:
get particles (e.g. protons, antiprotons,…)
accelerate them
throw them against each other
observe and record what happens
analyse and interpret the data
ingredients needed:
particle source
accelerator and aiming device
detector
trigger (decide what to record)
recording device
many people to:
design, build, test, operate accelerator
design, build, test, calibrate, operate, and understand detector
analyze data
lots of money to pay for all of this

32. How to get high energy collisions-
Need Ecom to be large enough to
allow high momentum transfer (probe small distances)
produce heavy objects (top quarks, Higgs boson)
e.g. top quark production: e+e- ® tt, qq ® tt, gg ® tt, …
Shoot particle beam on a target (“fixed target”):
Ecom = 2ÖEmc2 ~ 20 GeV for E = 100 GeV, m = 1 GeV/c2
Collide two particle beams (“collider :
Ecom = 2E ~ 200 GeV for E = 100 GeV - _ _ _ -
_____

33. How to make qq collisions, cont’d
However, quarks are not found free in nature!
But (anti)quarks are elements of (anti)protons.
So, if we collide protons and anti-protons we should get some qq collisions.
Proton structure functions give the probability that a single quark (or gluon) carries a fraction x of the proton momentum (which is 900 GeV/c at the Tevatron) _ -

34. Accelerator accelerators:
use electric fields to accelerate particles, magnetic fields to steer and focus the beams
synchrotron: particle beams kept in circular orbit by magnetic field; at every turn, particles “kicked” by electric field in accelerating station;
fixed target operation: particle beam extracted from synchrotron, steered onto a target
collider operation: accelerate bunches of protons and antiprotons moving in opposite direction in same ring; make them collide at certain places where detectors are installed

35. Fermilab accelerator complex

36. DÆ Upgrade Forward Scintillator + New Electronics, Trig, DAQ
New Solenoid, Tracking System
Si, SciFi,Preshowers
Shielding
Forward Mini-drift
chambers
Forward Scintillator
Central Scintillator
+ New Electronics, Trig, DAQ

37. Luminosity and cross section
Luminosity is a measure of the beam intensity (particles per area per second) ( L~1031/cm2/s )
“integrated luminosity” is a measure of the amount of data collected (e.g. ~100 pb-1)
cross section s is measure of effective interaction area, proportional to the probability that a given process will occur.
1 barn = cm2
1 pb = b = cm2 = m2
interaction rate:

38. Examples of particle detectors
photomultiplier:
photomultiplier tubes convert small light signal (even single photon) into detectable charge (current pulse)
photons liberate electrons from photocathode,
electrons “multiplied” in several (6 to 14) stages by ionization and acceleration in high electric field between “dynodes”, with gain  104 to 1010
photocathode and dynodes made from material with low ionization energy;
photocathodes: thin layer of semiconductor made e.g. from Sb (antimony) plus one or more alkali metals, deposited on glass or quartz;
dynodes: alkali or alkaline earth metal oxide deposited on metal, e.g. BeO on Cu (gives high secondary emission);

39. Examples of particle detectors
Spark chamber
gas volume with metal plates (electrodes); filled with gas (noble gas, e.g. argon)
charged particle in gas  ionization  electrons liberated;  string of electron - ion pairs along particle path
passage of particle through “trigger counters” (scintillation counters) triggers HV
HV between electrodes  strong electric field;
electrons accelerated in electric field  can liberate other electrons by ionization which in turn are accelerated and ionize  “avalanche of electrons”, eventually formation of plasma between electrodes along particle path;
gas conductive along particle path  electric breakdown  discharge  spark
HV turned off to avoid discharge in whole gas volume

40. Examples of particle detectors, contd
Scintillation counter:
energy liberated in de-excitation and capture of ionization electrons emitted as light - “scintillation light”
light channeled to photomultiplier in light guide (e.g. piece of lucite or optical fibers);
scintillating materials: certain crystals (e.g. NaI), transparent plastics with doping (fluors and wavelength shifters)
Geiger-Müller counter:
metallic tube with thin wire in center, filled with gas, HV between wall (-, “cathode”) and central wire (+,”anode”);  strong electric field near wire;
charged particle in gas  ionization  electrons liberated;
electrons accelerated in electric field  liberate other electrons by ionization which in turn are accelerated and ionize  “avalanche of electrons”; avalanche becomes so big that all of gas ionized  plasma formation  discharge
gas is usually noble gas (e.g. argon), with some additives e.g. carbon dioxide, methane, isobutane,..) as “quenchers”;

41. Particle detectors, cont’d
Scintillator:
energy liberated in de-excitation and capture of ionization electrons emitted as light - ``scintillation light'’
light channeled to photomultiplier in light guide (e.g. optical fibers);
scintillating materials: certain crystals (e.g. NaI), transparent plastics with doping (fluors and wavelength shifters)
proportional tube:
metallic tube with thin wire in center, filled with gas, HV between wall (-, “cathode”) and central wire (+,”anode”);  strong electric field near wire;
charged particle in gas  ionization  electrons liberated;
electrons accelerated in electric field  can liberate other electrons by ionization which in turn are accelerated and ionize  “avalanche of electrons” moves to wire  current pulse; current pulse amplified  electronic signal:
gas is usually noble gas (e.g. argon), with some additives e.g. carbon dioxide, methane, isobutane,..) as “quenchers”;

42. Particle detectors, cont’d
multi wire proportional chamber:
contains many parallel anode wires between two cathode planes (array of prop.tubes with separating walls taken out)
operation similar to proportional tube;
cathodes can be metal strips or wires  get additional position information from cathode signals.
drift chamber:
field shaping wires and electrodes on wall to create very uniform electric field, and divide chamber volume into “drift cells”, each containing one anode wire;
within drift cell, electrons liberated by passage of particle move to anode wire, with avalanche multiplication near anode wire;
arrival time of pulse gives information about distance of particle from anode wire; ratio of pulses at two ends of anode wire gives position along anode wire;

43. Particle detectors, cont’d
Cherenkov detector:
measure Cherenkov light (amount and/or angle) emitted by particle going through counter volume filled with transparent gas liquid, aerogel, or solid  get information about speed of particle.
calorimeter:
“destructive” method of measuring a particle's energy: put enough material into particle's way to force formation of electromagnetic or hadronic shower (depending on kind of particle)
eventually particle loses all of its energy in calorimeter;
energy deposit gives measure of original particle energy.
Note: many of the detectors and techniques developed for particle and nuclear physics are now being used in medicine, mostly diagnosis, but also for therapy.

44. Particle detectors, cont’d
Scintillator:
energy liberated in de-excitation and capture of ionization electrons emitted as light – “scintillation light'’
light channeled to photomultiplier in light guide (e.g. optical fibers);
scintillating materials: certain crystals (e.g. NaI), transparent plastics with doping (fluors and wavelength shifters)
proportional tube:
metallic tube with thin wire in center, filled with gas, HV between wall (-, “cathode”) and central wire (+,”anode”);  strong electric field near wire;
charged particle in gas  ionization  electrons liberated;
electrons accelerated in electric field  can liberate other electrons by ionization which in turn are accelerated and ionize  “avalanche of electrons” moves to wire  current pulse; current pulse amplified  electronic signal:
gas is usually noble gas (e.g. argon), with some additives e.g. carbon dioxide, methane, isobutane,..) as “quenchers”;

45. Particle detectors, cont’d
multi wire proportional chamber:
contains many parallel anode wires between two cathode planes (array of prop.tubes with separating walls taken out)
operation similar to proportional tube;
cathodes can be metal strips or wires  get additional position information from cathode signals.
drift chamber:
field shaping wires and electrodes on wall to create very uniform electric field, and divide chamber volume into “drift cells”, each containing one anode wire;
within drift cell, electrons liberated by passage of particle move to anode wire, with avalanche multiplication near anode wire;
arrival time of pulse gives information about distance of particle from anode wire; ratio of pulses at two ends of anode wire gives position along anode wire;

46. Particle detectors, cont’d
Cherenkov detector:
measure Cherenkov light (amount and/or angle) emitted by particle going through counter volume filled with transparent gas liquid, aerogel, or solid  get information about speed of particle.
calorimeter:
“destructive” method of measuring a particle's energy: put enough material into particle's way to force formation of electromagnetic or hadronic shower (depending on kind of particle)
eventually particle loses all of its energy in calorimeter;
energy deposit gives measure of original particle energy.
Note: many of the detectors and techniques developed for particle and nuclear physics are now being used in medicine, mostly diagnosis, but also for therapy.

47. Detectors
Detectors
use characteristic effects from interaction of particle with matter to detect, identify and/or measure properties of particle; has “transducer” to translate direct effect into observable/recordable (e.g. electrical) signal
example: our eye is a photon detector; (photons = light “quanta” = packets of light)
“seeing” is performing a photon scattering experiment:
light source provides photons
photons hit object of our interest -- some absorbed, some scattered, reflected
some of scattered/reflected photons make it into eye; focused onto retina;
photons detected by sensors in retina (photoreceptors -- rods and cones)
transduced into electrical signal (nerve pulse)
amplified when needed
transmitted to brain for processing and interpretation

48. Standard Model
A theoretical model of interactions of elementary particles
Symmetry:
SU(3) x SU(2) x U(1)
“Matter particles”
quarks
up, down, charm,strange, top bottom
leptons
electron, muon, tau, neutrinos
“Force particles”
Gauge Bosons
 (electromagnetic force)
W, Z (weak, elctromagnetic)
g gluons (strong force)
Higgs boson
spontaneous symmetry breaking of SU(2)
mass

49. Standard Model

50. Brief History of the Standard Model
Late 1920’s - early 1930’s: Dirac, Heisenberg, Pauli, & others extend Maxwell’s theory of EM to include Special Relativity & QM (QED) - but it only works to lowest order!
1933: Fermi introduces 1st theory of weak interactions, analogous to QED, to explain b decay.
1935: Yukawa predicts the pion as carrier of a new, strong force to explain recently observed hadronic resonances.
1937: muon is observed in cosmic rays – first mistaken for Yukawa’s particle
1938: heavy W as mediator of weak interactions? (Klein)
1947: pion is observed in cosmic rays
1949: Dyson, Feynman, Schwinger, and Tomonaga introduce renormalization into QED - most accurate theory to date!
1954: Yang and Mills develop Gauge Theories
1950’s - early 1960’s: more than 100 hadronic “resonances” have been observed !
1962 two neutrinos!
1964: Gell-Mann & Zweig propose a scheme whereby resonances are interpreted as composites of 3 “quarks”. (up, down, strange)

51. Brief History of the Standard Model (continued)
1970: Glashow, Iliopoulos, Maiani: 4th quark (charm) explains suppression of K decay into 
:spontaneous symmetry breaking (Higgs, Kibble)
1967: Weinberg & Salam propose a unified Gauge Theory of electroweak interactions, introducing the W±,Z as force carriers and the Higgs field to provide the symmetry breaking mechanism.
1967: deep inelastic scattering shows “Bjorken scaling”
1969: “parton” picture (Feynman, Bjorken)
: Gauge theories are renormalizable (t’Hooft, Veltman, Lee, Zinn-Justin..)
1972: high pt pions observed at the CERN ISR
1973: Gell-Mann & Fritzsch propose that quarks are held together by a Gauge-Field whose quanta, gluons, mediate the strong force Þ Quantum Chromodynamics
1973: “neutral currents” observed (Gargamelle bubble chamber at CERN)

52. Brief History of the Standard Model (continued)
1975: J/ interpreted as cc bound state (“charmonium”)
1974: J/ discovered at BNL/SLAC;
1976: t lepton discovered at SLAC
1977:  discovered at Fermilab in 1977, interpreted as bb bound state (“bottomonium”)  3rd generation
1979: gluon “observed” at DESY
1982: direct evidence for jets in hadron hadron interactions at CERN (pp collider)
1983: W±, Z observed at CERN (pp collider built for that purpose)
1995: top quark found at Fermilab (D0, CDF)
1999: indications for “neutrino oscillations” (Super-Kamiokande experiment)
2000: direct evidence for tau neutrino () at Fermilab (DONUT experiment)
2003: Higgs particle observed at Fermilab (?????) - -

53. Cathode ray history
1855 German inventor Heinrich Geissler develops mercury pump - produces first good vacuum tubes, these tubes, as
modified by Sir William Crookes, become the first to produce cathode rays, leading eventually to the discovery of the
electron (and a bit farther down the road to television).
1858 Julius Plücker shows that cathode rays bend under the influence of a magnet suggesting that they are connected in some way; this leads in 1897 to discovery that cathode rays are composed of electrons.
1865 H. Sprengel improves the Geissler vacuum pump. Plücker uses Geissler tubes to show that at lower pressure,
the Faraday dark space grows larger. He also finds that there is an extended glow on the walls of the tube and that
this glow is affected by an external magnetic field.
1869 J.W. Hittorf finds that a solid body put in front of the cathode cuts off the glow from the walls of the tube.
Establishes that "rays" from the cathode travel in straight lines.

54. 1871 C.F. Varley is first to publish suggestion that cathode rays are composed of particles. Crookes proposes that
they are molecules that have picked up a negative charge from the cathode and are repelled by it.
1874 George Johnstone Stoney estimates the charge of the then unknown electron to be about coulomb, close to
the modern value of x coulomb. (He used the Faraday constant (total electric charge per mole of
univalent atoms) divided by Avogadro's Number. James Clerk Maxwell had recognized this method soon after
Faraday had published, but he did not accept the idea that electricity is composed of particles.) Stoney also proposes
the name "electrine" for the unit of charge on a hydrogen ion. In 1891, he changes the name to "electron."
1876 Eugen Goldstein shows that the radiation in a vacuum tube produced when an electric current is forced through
the tube starts at the cathode; Goldstein introduces the term cathode ray to describe the light emitted.
1881 Herman Ludwig von Helmholtz shows that the electrical charges in atoms are divided into definite integral
portions, suggesting the idea that there is a smallest unit of electricity.

55. 1883 Heinrich Hertz shows that cathode rays are not deflected by electrically charged metal plates, which would
seem to indicate (incorrectly) that cathode rays cannot be charged particles.
1886 Eugen Goldstein observes that a cathode-ray tube produces, in addition to the cathode ray, radiation that travels
in the opposite direction - away from the anode; these rays are called canal rays because of holes (canals) bored in
the cathode; later these will be found to be ions that have had electrons stripped in producing the cathode ray.
1890 Arthur Schuster calculates the ratio of charge to mass of the particles making up cathode rays (today known as
electrons) by measuring the magnetic deflection of cathode rays. Joseph John (J.J.) Thomson first becomes interested
in the discharge of electricity through a gas a low pressure, that is to say, cathode rays.

56. 1892 Heinrich Hertz who has concluded (incorrectly) that cathode rays must be some form of wave, shows that the
rays can penetrate thin foils of metal, which he takes to support the wave hypothesis. Philipp von Lenard develops a
cathode-ray tube with a thin aluminum window that permits the rays to escape, allowing the rays to be studied in the
open air.
1894 J.J. Thomson announces that he has found that the velocity of cathode rays is much lower than that of light. He
obtained the value of 1.9 x 107 cm/sec, as compared to the value 3.0 x 1010 cm/sec for light. This was in response to
the prediction by Lenard that cathode rays would move with the velocity of light. However, by 1897, he distrusts this
measurement.
Special Note: At this time there was great rivalry between German and British researchers. As concerning the nature
of the cathode ray, the Germans tended to the explanation that cathode rays were a wave (like light), whereas the
British tended to believe that the cathode ray was a particle. As events unfold over the next few decades,
both will be
proven correct.

57. In fact, J.J. Thomson will be awarded the Nobel Prize in Physics in 1906 for proving the electron is a particle and his
son, George Paget Thomson, will be awarded the Nobel Prize in Physics in 1937 for showing that the electron is a
wave.
1895 Jean-Baptiste Perrin shows that cathode rays deposit a negative electric charge where they impact, refuting
Hertz's concept of cathode rays as waves and showing they are particles.
1896 Pieter P. Zeeman discovers that spectral lines of gases placed in a magnetic field are split, a phenomenon call
the Zeeman effect; Hendrik Antoon Lorentz explains this effect by assuming that light is produced by the motion of
charged particles in the atom. Lorentz uses Zeeman's observations of the behavior of light in magnetic field to
calculate the charge to mass ratio of the electron in an atom, a year before electrons are discovered and 15 years
before it is known that electron are constituents of atoms.