250 The Poetry of Physics and The Physics of Poetry
and antiΚ^0 were all spin 0 particles with baryon number 0. The η meson
was an unstable meson that decayed via the electromagnetic interaction
into 3 π mesons or a π meson and two photons. The baryons and mesons,
which form the class of hadrons or strongly interacting particles can be
grouped in families in which there are 8 members, 3 of which have the
same mass but different charges, two sets of two with the same mass but
different charges and one member with its own unique mass. As higher
energy collisions of protons with protons and mesons with protons were
performed new sets of baryons and mesons with the same structures but
greater spins began to be discovered. Among the mesons there were spin
1, 2, ... sets and among the baryons there were spin 3/2, 5/2, ... most of
which came in families of 8. Among the baryons there was another
family of 10. Murray Gell Mann and Yuval Ne’eman independently
showed that all of these families possessed the same symmetry, namely
that of SU(3), the special unitary group of degree 3.
Quarks
Murray Gell Mann and George Zweig independently in 1964 showed
that this symmetry could be explained if the hadrons were made up
of more elementary particles, which Gell Mann called quarks. In his
book, The Quark and the Jaguar, he describes how he came up with this
term, “In 1963, when I assigned the name ‘quark’ to the fundamental
constituents of the nucleon, I had the sound first, without the spelling,
which could have been ‘kwork’. Then, in one of my occasional perusals
of Finnegans Wake, by James Joyce, I came across the word ‘quark’ in
the phrase ‘Three quarks for Muster Mark’.”
Consistent with the SU(3) symmetry there are 3 kinds of quarks:
up down and strange of which the first generation of hadrons are
composed. The quarks were spin ½ particles that had the charges
respectively of +2/3e, –1/3e and –1/3 e. They differ from hadrons and
leptons such as electrons and muons in that their charges come in
multiples of e/3 instead of ±e as is the case for all other elementary
particles. The baryon number of quarks and antiquarks is 1/3 and –1/3
respectively whereas for all other elementary particles their baryon
numbers are +1, 0 or –1. There was also a set of 3 antiquarks with the
opposite charges of the quarks. The strange quark has strangeness
number +1 and the antistrange quark has strangeness number –1.
Baryons are made up of 3 quarks, antibaryons of 3 antiquarks and