# Topness

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Topness (T, also called truth), a flavour quantum number, represents the difference between the number of top quarks (t) and number of top antiquarks (t) that are present in a particle:

The top quark, also known as the t quark or truth quark, is the most massive of all observed elementary particles. Like all quarks, the top quark is a fermion with spin 1/2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. It has an electric charge of +2/3 e. It has a mass of 172.44 ± 0.13 (stat) ± 0.47 (syst)GeV/c2, which is about the same mass as an atom of tungsten. The antiparticle of the top quark is the top antiquark, which differs from it only in that some of its properties have equal magnitude but opposite sign.

## Contents

${\displaystyle T=n_{\text{t}}-n_{\bar {\text{t}}}}$

By convention, top quarks have a topness of +1 and top antiquarks have a topness of 1.The term "topness" is rarely used; most physicists simply refer to "the number of top quarks" and "the number of top antiquarks".

## Conservation

Like all flavour quantum numbers, topness is preserved under strong and electromagnetic interactions, but not under weak interaction. However the top quark is extremely unstable, with a half-life under 1023 s, which is the required time for the strong interaction to take place. For that reason the top quark does not hadronize, that is it never forms any meson or baryon, so the topness of a meson or a baryon is always zero. By the time it can interact strongly it has already decayed to another flavour of quark (usually to a bottom quark).

In particle physics, the strong interaction is the mechanism responsible for the strong nuclear force (also called the strong force, nuclear strong force, or colour force), and is one of the four known fundamental interactions, with the others being electromagnetism, the weak interaction, and gravitation. At the range of 10−15 m (1 femtometer), the strong force is approximately 137 times as strong as electromagnetism, a million times as strong as the weak interaction, and 1038 times as strong as gravitation. The strong nuclear force holds most ordinary matter together because it confines quarks into hadron particles such as the proton and neutron. In addition, the strong force binds neutrons and protons to create atomic nuclei. Most of the mass of a common proton or neutron is the result of the strong force field energy; the individual quarks provide only about 1% of the mass of a proton.

In particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms. The weak interaction serves an essential role in nuclear fission, and the theory regarding it in terms of both its behavior and effects is sometimes called quantum flavordynamics (QFD). However, the term QFD is rarely used because the weak force is better understood in terms of electroweak theory (EWT). In addition to this, QFD is related to quantum chromodynamics (QCD), which deals with the strong interaction, and quantum electrodynamics (QED), which deals with the electromagnetic force.

Half-life is the time required for a quantity to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay. The term is also used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The converse of half-life is doubling time.

## Related Research Articles

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## References

• Anchordoqui, L.; Halzen, F. (2009). "Lessons in Particle Physics". arXiv: [physics.ed-ph].

Francis Louis Halzen is a Belgian-American particle physicist, known for the development of the IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station in Antarctica which has been operational since 2010.

arXiv is a repository of electronic preprints approved for posting after moderation, but not full peer review. It consists of scientific papers in the fields of mathematics, physics, astronomy, electrical engineering, computer science, quantitative biology, statistics, mathematical finance and economics, which can be accessed online. In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository. Begun on August 14, 1991, arXiv.org passed the half-million-article milestone on October 3, 2008, and had hit a million by the end of 2014. By October 2016 the submission rate had grown to more than 10,000 per month.