10 Standard Model of the Particles and Forces
73
there is some new physics near the cut-off energy (four times the proton mass)
that should be added to the Fermi theory for it to make sense. A year later,
S. L. Glashow, John Illiopoulos and Luciano Maiani [47] revived the Bjorken–
Glashow idea of the charm quark and proposed that the weak interaction cutoff was merely the mass of the hypothetical charm quark near few GeV. The
first reference in this paper was to the cut-off paper of Marshak et al., just
mentioned. The charm quark had not been discovered in 1970; however, this
proved prophetic and the charm quark was discovered in 1974 as discussed
above.
In the subsequent years, the top (t) and bottom (b) quarks were suggested
as part of the standard model, by M. Kobayashi and T. Maskawa, in order to
accommodate the possibility of matter–anti-matter symmetry (CP) violation
in the standard model. They were discovered much later. So what happened to
hadron-lepton symmetry in the presence of top and bottom quarks? As it turns
out, two more leptons were discovered within a few years (see below). The
discovery of these extra two leptons completed the standard model. Predictions
of this theory seem to explain all experiments up to now. Thus the symmetry
between quarks and leptons that was a mere elegance requirement indeed
became part of the standard model as we know it now. It is essential for the
mathematical consistency of the theory, known in physics lingo as “anomaly
cancellation.” Kobayashi and Maskawa were awarded the Nobel Prize in 2008,
for connecting the top and bottom quark to CP violation. These last two
quarks were discovered at the Fermi National Accelerator laboratory in Batavia,
Illinois, much later. The current belief is that these six quarks are at the root
of all hadrons that exist and are produced in accelerators. The current version
of the standard model is based only on these quarks. Of course things could
change in future, as happens in physics so often.
10.2 The Quark Family and Their Interaction
One of the features of the standard model is that there are three sets of quarks—
with almost identical weak interaction properties (see Fig. 10.1). Each set is said
to belong to a family, with (t, b) being the heaviest (or third family), (c, s)
being the middle heavy (or second) family and (u, d) being the lightest in
weight (or the first family). The first question that comes to mind is: do these
families live separately without affecting each other or there is some interaction
among them (Fig. 10.2)? It turns out that they mix among themselves, which
means they transform from one to the other in different circumstances while
interacting via the weak force. In other words, a physical strange quark has a
73
there is some new physics near the cut-off energy (four times the proton mass)
that should be added to the Fermi theory for it to make sense. A year later,
S. L. Glashow, John Illiopoulos and Luciano Maiani [47] revived the Bjorken–
Glashow idea of the charm quark and proposed that the weak interaction cutoff was merely the mass of the hypothetical charm quark near few GeV. The
first reference in this paper was to the cut-off paper of Marshak et al., just
mentioned. The charm quark had not been discovered in 1970; however, this
proved prophetic and the charm quark was discovered in 1974 as discussed
above.
In the subsequent years, the top (t) and bottom (b) quarks were suggested
as part of the standard model, by M. Kobayashi and T. Maskawa, in order to
accommodate the possibility of matter–anti-matter symmetry (CP) violation
in the standard model. They were discovered much later. So what happened to
hadron-lepton symmetry in the presence of top and bottom quarks? As it turns
out, two more leptons were discovered within a few years (see below). The
discovery of these extra two leptons completed the standard model. Predictions
of this theory seem to explain all experiments up to now. Thus the symmetry
between quarks and leptons that was a mere elegance requirement indeed
became part of the standard model as we know it now. It is essential for the
mathematical consistency of the theory, known in physics lingo as “anomaly
cancellation.” Kobayashi and Maskawa were awarded the Nobel Prize in 2008,
for connecting the top and bottom quark to CP violation. These last two
quarks were discovered at the Fermi National Accelerator laboratory in Batavia,
Illinois, much later. The current belief is that these six quarks are at the root
of all hadrons that exist and are produced in accelerators. The current version
of the standard model is based only on these quarks. Of course things could
change in future, as happens in physics so often.
10.2 The Quark Family and Their Interaction
One of the features of the standard model is that there are three sets of quarks—
with almost identical weak interaction properties (see Fig. 10.1). Each set is said
to belong to a family, with (t, b) being the heaviest (or third family), (c, s)
being the middle heavy (or second) family and (u, d) being the lightest in
weight (or the first family). The first question that comes to mind is: do these
families live separately without affecting each other or there is some interaction
among them (Fig. 10.2)? It turns out that they mix among themselves, which
means they transform from one to the other in different circumstances while
interacting via the weak force. In other words, a physical strange quark has a