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Neutrino Mass Evidence - Student Project
Phys4410 Intro. to Nuclear and Particle Physics

[Neutrinos]   [History about Neutrinos]   [Experimental vs Theoretical]   [Reference]

 ¤ Brief History about Neutrinos

  • Experiment by Chadwick (1914)

β-ray spectra continuous not like α and γ ray spectra

  • Ellis & Meitner's Total Energy

Measurement of the total energy of the β decay spectrum

The total energy was less than the theoretical value and energy loss couldn't be explained by neutral gamma energy

Conclusion: missing energy only could be explained by Niels Bohr's statistical energy conservation or by the existence of a new particle.

  • Pauli's Suggestion of a New Particle - Neutron

A proton-electron of nitrogen nucleus with Z = 7 and atomic number = 14 required half integral total spin of 21 fermions. BUT, experimentally band spectra of nitrogen was spin = 1 (Obeyed Bose statistics).

Solution: Wolfgang Pauli's suggestion of a neutral fermion called "Neutron" with mass order of an electron mass and penetrating power stronger than a photon.

NEUTRINO - After Chadwick's discovery of heavy neutron in 1932, Fermi changed Pauli's neutron into NEUTRINO to distinguish from Chadwick's neutron.

  • Fermi & Perrin's Suggetion of Massless Neutrino

In 1934, Fermi developed a β-decay theory based on QED (Quantum Electrodynamics) of Dirac, Heisenburg, and Pauli.

Dirac's Theory: (= quantum mechanics + theory of special relativity) Prediction of positron, the first antiparticle, also the intrinsic spin of the electron.

  • Fermi-Gamow-Teller Theory

Gamow & Teller's suggestion of the axial vector current

ψ*γμγ5ψ (γ5 = -iγ0γ1γ2γ3)

to explain β-decay processes where the spin of initial and final nucleus differed (Fermi hinted this earlier.).

  • Yukawa's Particle

Yukawa's π meson decayed into μ meson.

The π meson & the μ meson had unique energy which implies the emission of a very low-mass neutral particle (muon decayed into an electron with a continuous β spectrum of its own.).

  • Neutrino Detection Impossible - Bethe & Peierls's Prediction

A strength of a weak interaction would occur a neutrino to pass through 50 billion miles of water without interaction.

  • Fred Reine's Address about Bethe & Peirels's Prediction

Fred Reines and C. Cowan searched a way to measure inverse β-decay:
e)* + p → n + e+ (* as anti)

Requirement: low-cross-section, large target, and enormous flux.

Experiment: Nuclear Fission to provide a large amount of antineutrino flux and resulting two 0.5 MeV γ-rays.

Result: Reines and Cowan sent a telegram in June 1956 informing Pauli of their discovery.

  • Neutrino found to be negative helicity (1957)

By Goldhaber, Grodzins and Sunyar: Neutrino Left handed

  • Bruno Pontecorvo's proposal (1957)

νν* oscillations analogously to K0K*0 (Later to be oscillations into sterile states.)

  • Evidence for a Second Type of Neutrino(1962, Brookhaven)
By L. Lederman, J. Steinberger, and M. Schwartz:
The Nobel Prize in Physics 1988 "for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino" → It is confirmed that νμ are different from νe

  • Introduction of Neutrino Flavour mixing and Flavour Oscillations

By Ziro Maki, Masami Nakagawa, and Sakata in 1962.

  • The First Experiment to Detect Solar Neutrinos

Ray Davis and his colleagues got first radiochemical solar neutrino results at Homestake Mine in North Dakoda in 1968.

  • The Discovery of Third Neutrino Type

Discovery of ντ at SLAC (the Stanford Linear Accelerator Center) by Martin Perl and his colleagues (1976? or 1978?)

Martin Perl and Frederick Reines won the Nobel Prize in 1995 for the discovery of the tau lepton and the detection of the neutrino, respectively.

  • In 1985.....

The IMB Experiment (Irvine Michigan Brookhaven Experiment), using H2O (Water) detector for the search of proton decay (also detects neutrinos) → Observation of fewer νμ-interactions than expected. → The anomaly is, at first, believed to be a detector error.

→ Atmospheric Neutrino Anomaly (Observed by IMB and Kamiokande)

Measurement of Non-zero νmass approx. 10-4 times the mass of the electron by Russian Team → BUT subsequent attempts of independent reproduce measurement FAIL.

  • Kamiokande group:

In 1986, confirms deficit by first directional counting observation of solar neutrinos.

In 1987, IMB experiment and Kamiokande detect the burst of the neutrinos from Supernova 1987A.

In 1988, Kamiokande's search for proton decay with improved results: distinguishable between νμ-interactions and νe-interactions.
Measurement of approx. 60% of the νμ-interactions

  • In 1989.....

Frejus and NUSEX (The Nucleon Stability EXperiment) used Iron target instead of water (H2O)
→ Reporting NO DEFICIT of νμ-interactions

LEP (Large Electron-Positron) Accelerator Experiment in Switzerland and the SLC (The Stanford Linear Collider) at SLAC (Stanford Linear Accelerator Center: founded in 1962.): Determined only 3 existing light neutrino species (νμ, ντ, νe)

Kamiokande: the Second Experiment to detect solar Neutrinos → Confirmation of the Long-Standing anomaly by finding approx. 1/3 of the expected interactions.

  • In 1990, IMB's confirmation of the DEFICIT of νμ-interaction

IMB experiment: upgrade → better ability to figure νμ-interaction

  • In 1991~2, Confirmation of the Solar Neutrino DEFICIT in radiochemical Experiment.

SAGE (The Russian-American Gallium Experiment, in Russia) and GALLEX (GALLium EXperiment, in Italy)

  • In 1994,.....

Kamiokande: Finds Deficit of high-energy νμ-interactions. → νμ traveling the longest distances from production point to the detector makes the largest depletion.

Kamiokande and IMB groups: Test of the ability of water detectors to distiguish between νμ-interactions and νe-interactions by using a test beam at KEK.

  • In 1996, SUPER-KAMIOKANDE activated for the search of neutrinos(Japan-US joint team; leader: Yoji Totsuka).

  • In 1998, Super-kamiokande team reports: found oscillation and therefore non-zero mass for νμ (Neutrino '98 Conference).

  • In 2000, DONUT - Observation of the ντ.

  • In 2001 ~ 2002,.....

SNO (The Sudbury Neutrino Observatory): Observation of Neutral Current, Charged Current, and Elastic Scattering from Solar neutrinos → Neutrino oscillations cause the Solar Neutrino Problem.

KamLAND (Kamioka Liquid scintillator Anti Neutrino Detector) started in January. After 10 months, announcement of a detection of a deficit of ν*e

in Japan.

[Neutrinos]   [History about Neutrinos]   [Experimental vs Theoretical]   [Reference]

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