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R. Barrett and P. P. Delsanto
Another substantial disagreement between the Standard Model and experimental measurement is in the model’s prediction of the proton radius, where
the discrepancy is enormous 8 . In this case, and also for the muon magnetic
moment, physicists are reluctant to attribute the discrepancies to the Standard
Model until all possible sources of error in the experimental measurements
have been eliminated.
As well as the discrepancies mentioned above, there are some physical
phenomena which are left completely unexplained by the Standard Model.
For instance, gravity remains steadfast in its refusal to be accommodated
in the same scheme as the other physical forces. Since Einstein, gravity has
been interpreted as arising from curvature in the space-time fabric within
which the other forces operate. This fundamental incompatibility between
quantum mechanics and relativity is one of the major embarrassments of
modern physics.
More recently, the growing evidence for dark matter and dark energy
throughout the universe (see Chap. 11) proposes another challenge for the
Standard Model. It might be expected that a theory of fundamental particles would provide an explanation for these two phenomena, but as currently
constituted, the Standard Model has no relevant mechanism. In addition,
a particle that has been around since the middle of the last century, the
neutrino, has been found to oscillate between three different flavours. Such
a characteristic requires the presence of mass, but in the Standard Model the
neutrino is massless. This disagreement is not yet resolved.
Much has been made of the discovery of the Higgs boson as a triumph for
the Standard Model. There are, however, other hadrons that are predicted at
very high energies by the Standard Model, and have not yet been observed. In
addition, “glueballs”, which are particles comprised solely from two or three
gluons, but no other hadrons, are predicted. Their detection would represent
a major coup for the Standard Model.
Other forms of “exotic” particles have indeed been discovered, including
pentaquarks and tetraquarks, composed of five and four individual quarks
respectively. Recently it was announced by CERN that a tetraquark
comprised of four charm quarks had been discovered [9]. It is a good candidate to test theories on whether the four quarks are tightly bound, or arranged
to form two mesons, which are stuck together loosely in analogy to a chemical
molecule.
Even though the Standard Model has had great success in establishing an
order in the chaos of the particle zoo, it has fundamental limitations. We
8 About seven standard deviations, corresponding to a 1 in 390 billion chance that the model and
measurement are in agreement.
R. Barrett and P. P. Delsanto
Another substantial disagreement between the Standard Model and experimental measurement is in the model’s prediction of the proton radius, where
the discrepancy is enormous 8 . In this case, and also for the muon magnetic
moment, physicists are reluctant to attribute the discrepancies to the Standard
Model until all possible sources of error in the experimental measurements
have been eliminated.
As well as the discrepancies mentioned above, there are some physical
phenomena which are left completely unexplained by the Standard Model.
For instance, gravity remains steadfast in its refusal to be accommodated
in the same scheme as the other physical forces. Since Einstein, gravity has
been interpreted as arising from curvature in the space-time fabric within
which the other forces operate. This fundamental incompatibility between
quantum mechanics and relativity is one of the major embarrassments of
modern physics.
More recently, the growing evidence for dark matter and dark energy
throughout the universe (see Chap. 11) proposes another challenge for the
Standard Model. It might be expected that a theory of fundamental particles would provide an explanation for these two phenomena, but as currently
constituted, the Standard Model has no relevant mechanism. In addition,
a particle that has been around since the middle of the last century, the
neutrino, has been found to oscillate between three different flavours. Such
a characteristic requires the presence of mass, but in the Standard Model the
neutrino is massless. This disagreement is not yet resolved.
Much has been made of the discovery of the Higgs boson as a triumph for
the Standard Model. There are, however, other hadrons that are predicted at
very high energies by the Standard Model, and have not yet been observed. In
addition, “glueballs”, which are particles comprised solely from two or three
gluons, but no other hadrons, are predicted. Their detection would represent
a major coup for the Standard Model.
Other forms of “exotic” particles have indeed been discovered, including
pentaquarks and tetraquarks, composed of five and four individual quarks
respectively. Recently it was announced by CERN that a tetraquark
comprised of four charm quarks had been discovered [9]. It is a good candidate to test theories on whether the four quarks are tightly bound, or arranged
to form two mesons, which are stuck together loosely in analogy to a chemical
molecule.
Even though the Standard Model has had great success in establishing an
order in the chaos of the particle zoo, it has fundamental limitations. We
8 About seven standard deviations, corresponding to a 1 in 390 billion chance that the model and
measurement are in agreement.