From electrons to quarks

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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
• http//www-d0.fnal.gov (Fermilab homepage)
• http//sg1.hep.fsu.edu/wahl/Quarknet/index.html
  (has links to many particle physics sites)
• http//www.fnal.gov/pub/tour.html
  (Fermilab particle physics tour)
• http//ParticleAdventure.org/
  (Lawrence Berkeley Lab.)
• http//www.cern.ch (CERN -- European Laboratory
  for Particle Physics)

Outline
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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 ???... ???

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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 10-10 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

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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?)

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• 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
• 1870s William Crookes (1832-1919) (London)
• detailed investigation of discharges
• Confirms Hittorfs findings about deflection in
  magnetic field
• Concludes that rays consist of particles carrying
  negative charge
• 1886 - 1887 Heinrich Hertz (1857-1894)
  (Karlsruhe)
• Built apparatus to generate and detect
  electromagnetic waves predicted by Maxwells
  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

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• 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

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• 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)

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• 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 (1845-1923) (Würzburg)
• Uses discharge tubes designed by Hittorf and
  Lenard (but improved pump) to verify Hertz and
  Lenards experiments
• Discovers X-rays -- forget about cathode rays!

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• Röntgen and X-rays

Hand of Anna Röntgen
From Life magazine,6 April 1896
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• 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 (1853-1928) (Leiden)
• Formulates atomistic interpretation of Maxwells
  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 (1865-1943) (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 (1861-1928) (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

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• 1897 Joseph John Thomson (1856-1940) (Cambridge)
• Improves on tube built by Perrin with Faraday cup
  to verify Perrins 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.

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• 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

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• 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 Plancks constant,
  ffrequency)
• ? 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 (1868-1963) (Chicago)
• Did not accept Einsteins explanation
• Tried to disprove it by precise measurements
• Result confirmation of Einsteins theory,
• measurement of h with 0.5 precision
• 1923 Arthur Compton (1892-1962)(St.Louis)
• Observes scattering of X-rays on electrons

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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 Marsdens SCATTERING EXPERIMENT
• (Geiger, Marsden, 1906 - 1911) (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) .

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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 lt 10-14 m, surrounded by electrons at
  ?10-10 m

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Rutherford model

• RUTHERFORD MODEL OF ATOM(planetary model of
  atom)
• positive charge concentrated in nucleus (lt10-14
  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 ? 10-10 s )
• ? we would not exist to think about this!!

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Beta decay

• 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
  1956-1958 (Cowan and Reines)

b decay n p e- ne
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• 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

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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

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Experimentalists ...

• Strange quark
• kaons discovered 1947

Not seen, but should be common
K0 production and decay in a bubble chamber
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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.

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Particle physics experiments

• 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

___________
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About Units

• Energy - electron-volt
• 1 electron-volt kinetic energy of an electron
  when moving through potential difference of 1
  Volt
• 1 eV 1.6 10-19 Joules 2.1 10-6 Ws
• 1 kWhr 3.6 106 Joules 2.25 1025 eV
• mass - eV/c2
• 1 eV/c2 1.78 10-36 kg
• electron mass 0.511 MeV/c2
• proton mass 938 MeV/c2
• professors mass (80 kg) ? 4.5 1037 eV/c2
• momentum - eV/c
• 1 eV/c 5.3 10-28 kg m/s
• momentum of baseball at 80 mi/hr
  ? 5.29 kgm/s ? 9.9 1027 eV/c

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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

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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 ee- 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

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How to make qq collisions, contd

• 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)

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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

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Fermilab accelerator complex
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DÆ Upgrade
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Luminosity and cross section

• Luminosity is a measure of the beam intensity
  (particles per
  area per second) (
  L1031/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 10-24 cm2
• 1 pb 10-12 b 10-36 cm2 10- 40 m2
• interaction rate

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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)

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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

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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

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Particle detectors, contd

• 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

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Particle detectors, contd

• 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

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Particle detectors, contd

• 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.

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Particle detectors, contd

• 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

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Particle detectors, contd

• 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

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Particle detectors, contd

• 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.

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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

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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

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Standard Model
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Brief History of the Standard Model

• Late 1920s - early 1930s Dirac, Heisenberg,
  Pauli, others extend Maxwells 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 Yukawas 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
• 1950s - early 1960s 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)

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Brief History of the Standard Model (continued)

• 1970 Glashow, Iliopoulos, Maiani 4th quark
  (charm) explains suppression of K decay into ??
• 1964-1967spontaneous 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)
• 1971-1972 Gauge theories are renormalizable
  (tHooft, 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)

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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
  (?????)

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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.

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• 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 10-20
  coulomb, close to
• the modern value of 1.6021892 x 10-19 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.

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• 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.

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• 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.

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• 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.