4
Order in the Zoo and Quarks
Physics always builds on simplicity of principle. Simple rules and laws often
help to explain complicated things as we move towards a fundamental theory.
It was therefore unacceptable to physicists that all the members of the zoo of
particles are truly fundamental. There must be a simpler set of ideas that would
explain them, and the obsession to find this started in the 1950s, and continued
to the 1960s. Mathematical techniques, already known to mathematicians as
group theory, started to come into the lingo of physicists.
4.1 Eightfold Way and Quarks Inside Baryons
and Mesons
The so-called eightfold way was suggested by Murray Gell-Mann and Yuval
Ne’eman in 1961, to put order into the particles zoo. The phrase “eightfold way” is derived from Buddhist teaching of eight ways to attain “nirvana” (or salvation). It put eight known particles similar to the proton
and neutron and those that are close by in mass together into a group.
They were (p, n, ,
± , ,
0 , ,, ,
− , ,
0 ). Similarly, he put the eight mesons
(π
± , π
0 , K
± , K
0 , ¯
K
0 , η) into another group. Group theory based on a group
called SU (3) predicted that all eight particles in the above group would
have the same mass but they did not. Understanding the small differences in
the particle masses in one group could be achieved using group theoretical
methods, suggested by Murray Gell-Mann and Susumu Okubo, in 1962,
confirming the eightfold way arrangement further. This went on to provide a
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_4
27
Order in the Zoo and Quarks
Physics always builds on simplicity of principle. Simple rules and laws often
help to explain complicated things as we move towards a fundamental theory.
It was therefore unacceptable to physicists that all the members of the zoo of
particles are truly fundamental. There must be a simpler set of ideas that would
explain them, and the obsession to find this started in the 1950s, and continued
to the 1960s. Mathematical techniques, already known to mathematicians as
group theory, started to come into the lingo of physicists.
4.1 Eightfold Way and Quarks Inside Baryons
and Mesons
The so-called eightfold way was suggested by Murray Gell-Mann and Yuval
Ne’eman in 1961, to put order into the particles zoo. The phrase “eightfold way” is derived from Buddhist teaching of eight ways to attain “nirvana” (or salvation). It put eight known particles similar to the proton
and neutron and those that are close by in mass together into a group.
They were (p, n, ,
± , ,
0 , ,, ,
− , ,
0 ). Similarly, he put the eight mesons
(π
± , π
0 , K
± , K
0 , ¯
K
0 , η) into another group. Group theory based on a group
called SU (3) predicted that all eight particles in the above group would
have the same mass but they did not. Understanding the small differences in
the particle masses in one group could be achieved using group theoretical
methods, suggested by Murray Gell-Mann and Susumu Okubo, in 1962,
confirming the eightfold way arrangement further. This went on to provide a
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_4
27