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Neutrinos: The Most Elusive Particles on Earth

Neutrinos: The Most Elusive Particles on Earth. Nikolai Tolich. What Are Fundamental Particles?. Atoms are composed of electrons (e - ), protons (p), and neutrons (n). The proton (p) was discovered by the New Zealander , Lord Ernest Rutherford.

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Neutrinos: The Most Elusive Particles on Earth

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  1. Neutrinos: The Most Elusive Particles on Earth Nikolai Tolich

  2. What Are Fundamental Particles? • Atoms are composed of electrons (e-), protons (p), and neutrons (n). • The proton (p) was discovered by the New Zealander, Lord Ernest Rutherford. • The invention of the bubble chamber in 1952 leads to an “explosion” of new particles. • 1964 Gell-Mann and Zweig put forth the idea of quarks, reducing the number of fundamental particles to 12.

  3. Expected Observed Electron Energy What Are Neutrinos? • In 1930 Pauli postulated the particle we now call the neutrino. A Poet’s Description: e- Neutrinos, they are very small.They have no charge and have no massAnd do not interact at all.The earth is just a silly ballTo them, through which they simply pass,Like dustmaids down a drafty hallOr photons through a sheet of glass.They snub the most exquisite gas,Ignore the most substantial wall,Cold shoulder steel and sounding brass,Insult the stallion in his stall,And, scorning barriers of class,Infiltrate you and me. Like tallAnd painless guillotines they fallDown through our heads into the grass.At night, they enter at NepalAnd pierce the lover and his lassFrom underneath the bed—you callIt wonderful; I call it crass.—John Updike 1960 Nucleus Nucleus’ e- ? Nucleus Nucleus’ • Pauli’s particle would have almost zero mass and be almost impossible to observe. • In 1956 the impossible happened as Reines and Cowan observed neutrinos from a nuclear reactor, for which they got the 1995 Nobel prize in physics.

  4. The Solar Neutrino Problem • The Sun is one large nuclear fusion reactor, converting Hydrogen nuclei into Helium nuclei, releasing energy according to Einstein’s famous E=mc2equation, and producing neutrinos. • In 1961 Ray Davis set out to measure the neutrinos from the Sun using 400,000 liters of cleaning fluid 1500 meters below the Earth’s surface in order to verify the solar model. • In 1968 Ray Davis announced that he only saw a fraction of the expected number of solar neutrinos, the start of the “The Solar Neutrino Problem”. • Since 1968 this measurement has been repeated by 6 experiments all giving a reduced flux.

  5. Neutrino Oscillations? • The experimental observation of less neutrinos than expected can be explained if neutrinos somehow change from one type to another between being produced and detected. • All the solar neutrino detectors were only sensitive to electron neutrinos. tau & muon neutrino electron neutrino electron neutrino • In 2002 the SNO experiment in Canada, sensitive to all types of neutrinos, confirmed that the total number of neutrinos from the Sun matched that predicted from the solar model.

  6. Neutrinos at KamLAND 80% of our neutrinos come from 140 to 210km away. KamLAND uses the entire Japanese nuclear power industry (~60 GW, or 4% of world’s manmade power, or 20% of the world’s nuclear power) as a neutrino source and doesn’t pay a dime. Kashiwazaki Takahama Ohi KamLAND

  7. Our Neutrino Detector 1km below the Earth’s surface Steel sphere Photomultiplier tubes, detect light produced by particles in the scintillator 1 kton Liquid-scintillator enclosed in a large plastic balloon, inner detector Outer detector designed to eliminate backgrounds

  8. Building The Detector

  9. KamLAND Data • The total amount of light detected is proportional to the particle’s energy. Outer Detector • The arrival time of the light allows us to determine where the particle is. Inner Detector Light Intensity Time

  10. ne Detecting Neutrinos at KamLAND • Neutrinos produce a very distinctive signature. 1 MeV 2.2 MeV n e- e+ p p • One neutrino out of every 100,000,000,000,000,000 (1017) passing through KamLAND collides with a proton. • Despite these odds, the number of neutrinos produced at nuclear power plants is large enough for us to expect to detect about 1 to 2neutrinos per day.

  11. Observed Neutrino Spectrum

  12. Neutrino Disappearance From Reactors Solar Experiments

  13. Conclusions • In 2002 SNO proved that neutrinos coming from the Sun consisted of all three types of neutrinos, not just electron neutrinos. • In the same year KamLAND found for the first time disappearance of electron neutrinos from a man made sources as a function of distance. • This evidence taken together strongly suggests the existence of neutrino oscillations, which require the neutrino to have mass. • We have measured the difference in mass between the different types of neutrinos to be 0.000000016 (1.6*10-8) times the electron mass. • The absolute mass of any neutrino will have to be measured by future experiments.

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