Structure of matter, 8

Authors

David Peak, Utah State UniversityFollow

Document Type

Course

Journal/Book Title/Conference

Physics 3710 – Intermediate Modern Physics, Spring 2018

Publication Date

1-8-2018

First Page

1

Last Page

3

Abstract

Neutrino mass and family mixing

Neutrinos are products of radioactive decay in many stellar fusion processes, primarily starting with the reaction p + p → ²He*→ ²H + e⁺ +ν_e . The nucleus ²He* is a highly unstable (that’s what the * represents) isotope of helium consisting of four primary u quarks and two primary d quarks. For years (since 1962 or so), various groups have been measuring the solar electron-neutrino flux, invariably observing it to be lower than theoretical predictions. Moreover, neutrinos are generated in the upper atmosphere, via collisions of cosmic ray particles with atmospheric atoms, and in nuclear reactors and some accelerator reactions. Attempts to measure one or other type of neutrino in these circumstances, when the evidence is clean, typically show deficits from expectation. “Explanations” for these neutrino deficits have been plentiful, but, in the end, only one appears to be generally applicable: neutrino oscillations. The idea is that a u quark in the short-lived ²He* nucleus converts into a d quark by emitting a W⁺ that, in turn, decays into the positron and the electron-neutrino. Doing so presumably reduces the electric repulsion in the nucleus sufficiently that the otherwise forbidden reaction u → d + e⁺ +ν_e actually occurs. (The reaction doesn’t reduce the electric repulsion enough in a single proton, so it doesn’t occur in protons by themselves; that’s good for us!)

Recommended Citation

Peak, David, "Structure of matter, 8" (2018). Structure of Matter. Paper 8.
https://digitalcommons.usu.edu/intermediate_modernphysics_matter/8