topquark

The top quark, denoted t, is a fundamental particle in the Standard Model of particle physics. It is an up-type quark and the third generation partner of the bottom quark, making it the heaviest known elementary particle. Like other quarks, it carries electric charge +2/3e and is a color triplet, participating in strong interactions.

The top quark has a mass around 173 GeV/c^2 and a spin of 1/2. It has an extremely short lifetime, of order 5×10^-25 seconds, which is shorter than the timescale for hadronization. As a result, it decays as a bare quark, predominantly into a W boson and a bottom quark (t → W b). The decay rate is governed by the CKM matrix element V_tb, which is measured to be very close to unity, indicating that top quarks almost always decay to W b.

Top quarks are produced in high-energy hadron collisions. They are primarily created in pairs via the strong interaction (pp or p¯p collisions producing t t¯), but can also be produced singly through electroweak processes (single top production). The dominant decay products depend on the subsequent decay of the W bosons, leading to various leptonic or hadronic final states. Top quark production and decay rates are measured to test quantum chromodynamics and the electroweak sector, and to constrain new physics.

The top quark plays a crucial role in the Standard Model, particularly in studies of the Higgs sector and electroweak radiative corrections. Its large mass implies a substantial Yukawa coupling to the Higgs field and makes precision top quark measurements important for understanding the stability of the electroweak vacuum and for searches for physics beyond the Standard Model.

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