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The History of “Anomalous” Atmospheric Neutrino Events: A First Person Account


The modern picture of the neutrino as a multiple-mass, highly mixed neutral particle has emerged over forty years of study. Best known of the issues leading to this picture was the apparent loss of neutrinos coming from the sun. This article describes another piece of evidence that supports the picture; the substantial reduction of high-energy muon-type neutrinos observed in nature. For much of the forty-year period before the modern picture emerged, this observation was known as the “atmospheric neutrino anomaly,” since these neutrinos originate in the Earth’s atmosphere. This paper describes the discovery of the atmospheric neutrino anomaly. I explore the scientific context and motivations in the late 1970s, from which this work emerged. The gradual awareness that the observations of atmospheric neutrinos were not as expected took place in the 1983–1986 period.

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  1. I will frequently use the terms neutrino mixing and neutrino oscillations interchangeably, since oscillations require mixing. Neutrino mass differences are also required for the mixing to manifest itself as a time- and distance-dependent variation in the neutrino properties, an oscillation.


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  40. Ibid., 1989.

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  47. Ibid.

  48. Takaaki Kajita (PhD dissertation, University of Tokyo, 1986). UTICEPP-86-03.

  49. Ibid.

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  55. Kajita (ref. 48).

  56. Hirata et al., “Atmospheric Neutrino Flux” (ref. 50).

  57. Kajita (ref. 48).

  58. Hirata et al., “Atmospheric Neutrino Flux” (ref. 50).

  59. J. LoSecco, email to Totsuka, April 18, 1989.

  60. Y. Totsuka and T. Kajita, letter, August 12, 1989.

  61. Fred Reines, private communication, used with permission.

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I would like to thank Allan Franklin for his encouragement. In particular, I benefited from many suggestions he made on an early version of this manuscript. The Physics in Perspective editors have done a remarkable job in helping to make the article accessible.

The work described in this paper would have been impossible without the contributions of many people, and it is necessary to recognize them in closing. Larry Sulak, Fred Reines, Maurice Goldhaber, and Jack Van der Velde provided the leadership for the IMB experiment, which was in many ways the first large-scale experiment in astro-particle physics. Many creative and hardworking people have contributed. Most have been mentioned in the article but should also be recognized here. Students Bruce Cortez, Bill Foster, Eric Shumard, Geoff Blewitt, and Todd Haines all played an important role. The next generation included Dave Casper, Steve Dye, and Clark McGrew, who helped confirm the result with the IMB-3 data and some new, independent particle classification methods. Richard Bionta was a master at calibration and designed and constructed the system that converted raw detector information into useful physical observations. Tegid W. Jones, Danka Keilczewska, and John Learned have provided brilliant independent interpretations of the various observations. Many additional members of the IMB collaboration contributed to its success. M. Koshiba, Y. Totsuka, and T. Kajita have always shown a willingness to discuss physics even if they did not always share my point of view. Steve Weinberg, Shelley Glashow, Howard Georgi, Abdus Salam, and Jogesh Pati provided solid theoretical motivation for the project as well as enthusiastic support.

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Correspondence to John M. LoSecco.

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John M. LoSecco is a professor of physics at the University of Notre Dame. He has also worked at Harvard University, the University of Michigan, and the California Institute of Technology. Astro-particle physics is one of his research interests. This paper is based on a talk presented at the Larry Sulak Festschrift, “The Golden Age of Particle Physics and its Legacy,” Boston University, October 21–22, 2005.

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LoSecco, J.M. The History of “Anomalous” Atmospheric Neutrino Events: A First Person Account. Phys. Perspect. 18, 209–241 (2016).

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  • Neutrino Mass
  • Neutrino Oscillation
  • Proton Decay
  • Grand Unify Theory
  • Atmospheric Neutrino