What is a Neutrino?
       Bradley J. Wogsland
      University of Tennessee




                                    What ...
Quantum Weirdness

                        λ = h/p
●   Quanta are not particles
    –   But can be approximated as such in...
Examples
●   Monsieur de Broglie
    –   riding his bicycle at about 25 mph would have a
        wavelength λ ≈ 10-37m (an...
Wolfgang Pauli

                                     ●   Made up neutrino to
                                         cons...
The Standard Model
●   Tabulation of the
    results of “particle”
    physics
●   Like the periodic table
    in Chemistr...
The Weak Interaction
●   Allows quarks & leptons to change flavor
●   For example, neutron decay can be written
          ...
Massive Particles
●   Must travel at subluminal velocities
●   How fast they travel through the vacuum at a
    given ener...
Bruno Pontecorvo
      ●   Born in 1913 (Pisa, Italy)
      ●   Worked under Fermi
      ●   Fled Italian fascism to North...
Pontecorvo's Idea
●   The mass eigenstates of neutrinos don't
    correspond to the flavor eigenstates.
●   This is expres...
Geometrically




θ12 ≈ π/6   θ23 ≈ π/4   θ13 ≈ 0 (< .2)
Quarks do it,too
●   This is expressed by the CKM matrix:

          [d] [.97 .22 .0037] [d m]
          [s] ≈ [.22 .97 .0...
Mass Differences
●   So far, only the differences between the mass
    eigenstates can be measured
●   |∆m12| ≈ 9 meV
●   ...
Neutrino Mass Hierarchies


        2
       m3                                              2
                           ...
So what is a neutrino?

A massive neutral lepton that interacts weakly. To
 calculate its propagation, use the mass basis....
An Analogy
●   An electron is a spin-½ particle
●   We can measure this spin either up or down
●   Nevertheless, an electr...
Don't be surprised when neutrino oscillations
        become a textbook example of a macroscopic
                        q...
A Few BIG Questions Remain
●   What are the actual neutrino mass eigenstates?
    –  Currently we can only measure the
   ...
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Neutrinos

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A discussion of the basic quantum mechanics behind neutrino mixing.

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Neutrinos

  1. 1. What is a Neutrino? Bradley J. Wogsland University of Tennessee What am I? ν
  2. 2. Quantum Weirdness λ = h/p ● Quanta are not particles – But can be approximated as such in limit of large momenta ● Quanta are not waves – But can be approximated as such in limit of low momenta
  3. 3. Examples ● Monsieur de Broglie – riding his bicycle at about 25 mph would have a wavelength λ ≈ 10-37m (and about 1030 eV/c momentum) ● Photons – visible light at λ ≈ 500nm has about 2.5 eV/c per photon ● Neutrinos...
  4. 4. Wolfgang Pauli ● Made up neutrino to conserve lepton number ● n → p+ + e- + νe ● Had already worked for Dirac vis a vis the positron Pauli & Bohr at the top of physics
  5. 5. The Standard Model ● Tabulation of the results of “particle” physics ● Like the periodic table in Chemistry ● A good guide, but starting to get a little too stretched at the seams...
  6. 6. The Weak Interaction ● Allows quarks & leptons to change flavor ● For example, neutron decay can be written - d(ud) → u(ud) + e + νe ● (quarks not involved in the decay but still bound in the baryon are in parentheses) ● Similar c to s and t to b reactions also occur
  7. 7. Massive Particles ● Must travel at subluminal velocities ● How fast they travel through the vacuum at a given energy depends on the mass -iEt |ψ(t)> = e |ψ(0)> E= p m 2 2 with
  8. 8. Bruno Pontecorvo ● Born in 1913 (Pisa, Italy) ● Worked under Fermi ● Fled Italian fascism to North America in the mid-1930's ● Proposed inverse β-decay detection of neutrinos in 1946 via 37 ● Cl + νe → 37Ar + e- ● Fled to the USSR after arrest of Klaus Fuchs in 1950 ● Predicted neutrino oscillations in 1957 ● Dies in 1993 (Dubna, Russia)
  9. 9. Pontecorvo's Idea ● The mass eigenstates of neutrinos don't correspond to the flavor eigenstates. ● This is expressed by the PMNS matrix: [v1] [3/4 -1/8 1/8 ] [v e] [v2] ≈ [1/4 3/8 -3/8 ] [v μ] [v3] [ 0 1/2 1/2 ] [v τ] (All terms are squareroots)
  10. 10. Geometrically θ12 ≈ π/6 θ23 ≈ π/4 θ13 ≈ 0 (< .2)
  11. 11. Quarks do it,too ● This is expressed by the CKM matrix: [d] [.97 .22 .0037] [d m] [s] ≈ [.22 .97 .04 ] [s m] [b] [ 0 .04 .99 ] [b m] (Here the weak eigenstates are on the left) ● Note that there is almost no mixing in this case
  12. 12. Mass Differences ● So far, only the differences between the mass eigenstates can be measured ● |∆m12| ≈ 9 meV ● |∆m32| ≈ 50 meV ● Overall upper bound ~200meV
  13. 13. Neutrino Mass Hierarchies 2 m3 2 m2 m12 m21 2 m32 2 m32 2 2 m2 m2 21 (0.00 eV )22 (0.20 (0.10 (0.23 2 m12 m3 “Verted” “Inverted”
  14. 14. So what is a neutrino? A massive neutral lepton that interacts weakly. To calculate its propagation, use the mass basis. To calculate its probability of interacting weakly, use the flavor basis. What am I? Really? ν
  15. 15. An Analogy ● An electron is a spin-½ particle ● We can measure this spin either up or down ● Nevertheless, an electron can be in a state where it has a certain probability to be up and a certain probability to be down ● Generally, we don't think of spin up and spin down electrons as two different particles, but as electrons with different spin orientations
  16. 16. Don't be surprised when neutrino oscillations become a textbook example of a macroscopic quantum effect. Recommended reading: Neutrino Oscillations for Dummies
  17. 17. A Few BIG Questions Remain ● What are the actual neutrino mass eigenstates? – Currently we can only measure the differences. ● Is the neutrino its own antiparticle? – Majorana or Dirac question ● Is there a deeper reason for so much mixing, unlike the quark case? ● How did this craft of junk cross the Atlantic?
  1. ¿Le ha llamado la atención una diapositiva en particular?

    Recortar diapositivas es una manera útil de recopilar información importante para consultarla más tarde.

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