What does a top quark decay into?
What does a top quark decay into?
In the Standard Model, the top quark decays via the weak interaction into a W boson and a down-type quark.
What happens when quarks decay?
The positive W* decays to a positron and an electron neutrino, and the negative W* to an electron and antineutrino as can be seen in the example reactions above. The decay of the up quark above is important in the proton-proton cycle of nuclear fusion.
Why is the top quark so massive?
So, according to the theory, the top quark is so heavy because it is the closest fundamental particle. Other physicists have suggested that the Higgs, the theoretical particle that gives other particles mass, is actually made up of pairs of heavy top quarks bound together.
Does the Higgs decay to top quark pairs?
The Higgs boson interacts only with massive particles, yet it was discovered in its decay to two massless photons. Quantum mechanics allows the Higgs to fluctuate for a very short time into a top quark and a top anti-quark, which promptly annihilate each other into a photon pair.
Can up quark decay?
Up and down quarks can decay into each other by emission of a W boson (this is the origin of beta decay due to the fact that the W can, depending on its type, decay into electrons, positrons and electron (anti-)neutrinos, ). The current understanding of quarks is, that they are a fundamental particle.
What are the properties of the top quark?
The lepton, neutrino and b quark from the decay of the top quark (and subsequent decay of the W) have some particular kinematic properties. The lepton for example tends to be very energetic compared to leptons coming from other decays.
How are top quarks produced in the standard model?
The Standard Model gives scientists guidance on how the top quark will be produced and how it will decay. From the theory, we expect top quarks to be produced predominantly in pairs. The top quark existence is very short. It decays into a lighter mass b quark and a W boson.
How is the mass of the top quark predicted?
Since the top quark mass is not predicted by the Standard Model (actually the SM doesn’t predict any particle mass), the theory allows prediction of the cross section in terms of the top quark’s mass. The graph to the right plots the top quark pair production cross section versus its mass (with a cross corresponding to the uncertainties.)
Why are top quarks rare in the universe?
The fact that top quark are very rare, translates into a very small cross section and is therefore measured in picobarns (pb = 10^-12 b), this is a million million times smaller than a large nucleus! One of the main reason why there is a small probability of producing top quarks is because they are very heavy.