Mesotron Decays and the Role of Anomalies Page: 1 of 10
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Mesotron Decays and the Role of Anomalies
William A. Bardeen
Theoretical Physics Department
Fermilab, MS 106, P.O. Box 500
Batavia, IL 60510, USA
March 15, 2007
Puzzles associated with Yukawa's mesotron theory of nuclear interactions led to the dis-
covery of "anomalies" in quantum field theory. I will discuss some of the remarkable conse-
quences of these anomalies in the physics of elementary particles.
In 1935 Hideki Yukawa postulated that nuclear forces were ascribed to a new massive scalar
field that coupled to neutrons to protons. To explain the saturation of the nuclear forces, the new
mesotrons were required to have a mass of order 200 me, and a coupling a few times larger than
that associated with the electric charge. The terms mesotron was used to describe a particle of
intermediate mass, much heavier than the light electron and much lighter than the neutron and
proton, the constituents of the atomic nucleus.
Indeed, in 1937, a new meson of intermediate mass was discovered as the dominant part of the
hard component of cosmic rays. It was natural to associate this meson with the field that Yukawa
had proposed to explain the nuclear force.
Shoichi Sakata played an important role in the struggle to understand the physics of the new
Yukawa mesotrons and their relation to the new mesons seen in cosmic rays.
Early estimates of the lifetime of the mesotron were based on Fermi's theory of j3-decay. These
estimates, in the range of 10-s to 10-7 sec, were considerably shorter than the lifetime observed for
the cosmic ray mesons, ~2 10-6 sec. This discrepancy was the focus of several papers by Yukawa,
Sakata and collaborators [1, 2].
Sakata also speculated on the lifetime of a neutral mesotron (Neutretto) whose existence was
suggested by the charge independence of the nuclear force. Sakata and Tanikawa suggested these
neutral mesotrons should decay to photons via the following process:
"First a neutral mesotron is absorbed by a proton which is in the negative energy state
and produces a (virtual) pair of a proton and an antiproton. Then this pair disappears
with the emission of more than two photons"
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Bardeen, William A. Mesotron Decays and the Role of Anomalies, article, March 1, 2007; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc889357/m1/1/: accessed December 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.