Properties of the top quark

The top quark, the heaviest elementary particle known to date, was discovered by the CDF and D0 collaborations in 1995. In more than 25 years since the discovery the properties of the top quark have been studied in detail.

[edit] Introduction

The top quark is one of six known quarks in the Standard Model theory. It is an 'up-type' quark, and is believed to have the same properties as the up (u) and charm (c) quarks, except for its mass.

The Standard Model of particle physics describes the interactions between the elementary building blocks of matter: quarks and leptons.

Six quark flavors, color charge and [1]

Top quark discovery

[edit] Top quark mass

The mass of the top quark is a free parameter of the Standard Model, and its value is not predicted directly by the theory. The exact value of its mass, however, has big consequences for how the top quark manifests itself in direct experimental observations and in the way it affects other particles and processes.

With an observed of 172.5 +- 0.3 GeV [] it is the heaviest point-like particle known, surpassing the Higgs boson (125.x +-y GeV), W () and Z () bosons. Compared to other fermions (quarks, charged leptons, neutrinos), the difference in mass is even more striking. The second-heaviest quark is the bottom quark, with a mass of XX+-YY GeV. As the mass is higher than the W boson mass + b quark mass combined, the top quark decay is able to decay to an on-shell W boson and a b-quark. It does so 99.x % of the time, with a very short lifetime of XX. the following plot (credit: tikz.org) compares mass and liftetime of elementary (and a few composite) particles known:

Figure 1: Diagram comparing lifetime and mass of the top quark (t), with a selection of other known elementary (and a few composite) particles (credit:tikz.org.