[4][verification needed] The antiparticle of the top quark is the top antiquark (symbol: t, sometimes called antitop quark or simply antitop), which differs from it only in that some of its properties have equal magnitude but opposite sign.

As such, the top quark's properties are extensively studied as a means to discriminate between competing theories of new physics beyond the Standard Model.

[b][6] In 1973, Makoto Kobayashi and Toshihide Maskawa predicted the existence of a third generation of quarks to explain observed CP violations in kaon decay.

[9][10] The proposal of Kobayashi and Maskawa heavily relied on the GIM mechanism put forward by Sheldon Glashow, John Iliopoulos and Luciano Maiani,[11] which predicted the existence of the then still unobserved charm quark.

When in November 1974 teams at Brookhaven National Laboratory (BNL) and the Stanford Linear Accelerator Center (SLAC) simultaneously announced the discovery of the J/ψ meson, it was soon after identified as a bound state of the missing charm quark with its antiquark.

[12] With the acceptance of the GIM mechanism, Kobayashi and Maskawa's prediction also gained in credibility.

Their case was further strengthened by the discovery of the tau by Martin Lewis Perl's team at SLAC between 1974 and 1978.

It was in fact not long until a fifth quark, the bottom, was discovered by the E288 experiment team, led by Leon Lederman at Fermilab in 1977.

[17] Early searches for the top quark at SLAC and DESY (in Hamburg) came up empty-handed.

As the SPS gained competition from the Tevatron at Fermilab there was still no sign of the missing particle, and it was announced by the group at CERN that the top mass must be at least 41 GeV/c2.

[17] The Tevatron was (until the start of LHC operation at CERN in 2009) the only hadron collider powerful enough to produce top quarks.

[17] It is the development of techniques that ultimately allowed such precision calculations that led to Gerardus 't Hooft and Martinus Veltman winning the Nobel Prize in physics in 1999.

[18][19] Because top quarks are very massive, large amounts of energy are needed to create one.

In a collision, a highly energetic gluon is created, which subsequently decays into a top and antitop.

However, these processes are predicted to be much rarer and have a virtually identical experimental signature in a hadron collider like Tevatron.

The production of single top quarks via weak interaction is a distinctly different process.

The main significance of measuring these production processes is that their frequency is directly proportional to the |Vtb|2 component of the CKM matrix.

[25] Since this ratio is equal to |Vtb|2 according to the Standard Model, this gives another way of determining the CKM element |Vtb|, or in combination with the determination of |Vtb| from single top production provides tests for the assumption that the CKM matrix is unitary.

[26] The Standard Model also allows more exotic decays, but only at one loop level, meaning that they are extremely rare.

[27] However, searches for these exotic decay modes have produced no evidence that they occur, in accordance with expectations of the Standard Model.

Fermions interact with this field in proportion to their individual coupling constants yi, which generates mass.

This hierarchy in the fermion masses remains a profound and open problem in theoretical physics.

The Higgs–Yukawa couplings of the up, down, charm, strange and bottom quarks are hypothesized to have small values at the extremely high energy scale of grand unification, 1015 GeV.

They increase in value at lower energy scales, at which the quark masses are generated by the Higgs.

One of the prevailing views in particle physics is that the size of the top-quark Higgs–Yukawa coupling is determined by a unique nonlinear property of the renormalization group equation that describes the running of the large Higgs–Yukawa coupling of the top quark.

The top-quark Yukawa coupling lies very near the infrared fixed point of the Standard Model.

The value of the top quark fixed point is fairly precisely determined in the Standard Model, leading to a top-quark mass of 220 GeV.

This is about 25% larger than the observed top mass and may be hinting at new physics at higher energy scales.

The quasi-infrared fixed point subsequently became the basis of top quark condensation and topcolor theories of electroweak symmetry breaking, in which the Higgs boson is composed of a pair of top and antitop quarks.

The predicted top-quark mass comes into improved agreement with the fixed point if there are additional Higgs scalars beyond the standard model and therefore it may be hinting at a rich spectroscopy of new Higgs fields at energy scales that can be probed with the LHC and its upgrades.