Neutrino Mass: Sentence Outline

Abstract. Long assumed to be massless, the ubiquitous yet ghostly neutrino may have some substance after all. After a brief introduction to the tiny subatomic particle, I discuss two popular methods of measuring its mass: direct measurement and indirect via detection of so-called "neutrino oscillations." Promising claims of nonzero mass from indirect measurements are presented, along with implications for particle physics, solar dynamics, and the ultimate fate of the universe.
  1. "Invented" in 1930 by Wolfgang Pauli to account for energy seemingly lost in the neutron decay process, the neutrino long evaded detection.
  2. Pauli assumed a precisely zero neutrino mass. Testing this assumption is even harder than detecting a neutrino, primarily because the mass is zero or almost zero.
  3. While direct approaches remain severely limited, indirect measurement has made substantial progress recently by successfully detecting the phenomenon called neutrino "mixing" or "oscillation" [2]
  4. The principle seems clear enough theoretically, but how can these oscillations be detected in practice?
  5. Measuring a nonzero mass is significant for several reasons, not least of which is simply that particle physicists have assumed the contrary since 1930.
  6. The idea of neutrino oscillations, long thought to be only of theoretical interest but now apparently vindicated by experiments, has carried mass measurements beyond conventional approaches.

[1] David Griffiths, Introduction to Elementary Particles (Wiley, New York, 1987), pp. 22-28.
[2] John Learned, "Discovery of Neutrino Oscillations and Mass" (Online:,jgl/neutrino news.html), June 1998.
[3] Wick C. Haxton and Barry R. Holstein, hep-ph/9905257, (1999).