Top Quark
Composition :
Statistics :
Generation :
Family :
Interaction forces :
Symbol :
Antiparticle :
Mass :
Decays into :
Electric charge :
Color charge
Spin :
Weak isospin :
Weak hypercharge :
Elementary particle
Fermionic
Third
Quark
strong, weak,
electromagnetic force
gravity
t
Strange Antiquark ( t ̅)
172.76 MeV/c²
bottom quark (99.8%)
strange quark (0.17%)
down quark (0.007%)
+ ²∕₃ e
Yes
¹/₂
LH : - ¹/₂, RH : 0
LH : + ¹/₃, RH : +⁴∕₃
+ 0.3
- 0.3
TOP QUARK
General
Quantum Numbers:
Electric Charge (Q): +2/3 (positive two-thirds elementary charge)
Baryon Number (B): 1/3 (one-third)
Strangeness (S): 0 (non-strange quark)
Isospin (I3): -1/2 (negative one-half)
Spin (S): 1/2 (intrinsic angular momentum)
Mass and Energy:
The top quark is the most massive of all quarks, with a mass of approximately 173 GeV/c² (Giga-electronvolts per speed of light squared). Its mass is significantly larger than that of other quarks, which results in a unique set of properties and behaviors.
Quantum Mechanics:
In the framework of quantum mechanics, the top quark is described as a point-like particle with quantized properties such as spin and charge. Its quantum state can be represented by a wave function, which provides information about the probability of finding the quark at different positions in space and time.
Quantum Field Theory:
The top quark is a fundamental component of the Standard Model of particle physics, which is described by quantum field theory. In this framework, the top quark is a constituent of the quark field, one of the basic quantum fields that permeate all of space. This field theory explains how quarks interact via the exchange of force-carrying particles, such as gluons (mediators of the strong nuclear force).
Strong Force Interaction:
Top quarks interact through the strong nuclear force, which is described by quantum chromodynamics (QCD). This interaction is responsible for binding quarks together to form hadrons. However, top quarks do not combine to form stable hadrons due to their extremely short lifetime. Instead, they rapidly decay before hadronization can occur.
Creation and Annihilation:
Top quarks can be created in high-energy processes, such as particle collisions in accelerators. Due to their large mass, top quark production requires very high energies to overcome their mass-energy barrier. In nature, top quarks are created in cosmic-ray interactions in Earth's atmosphere.
Decays and Short Lifetime:
Top quarks have an exceptionally short lifetime, with a mean lifetime of about 5 x 10^(-25) seconds. They decay through the weak force primarily to a W boson and a bottom quark (b). This process is governed by the electroweak interaction.
Combinations with top quarks
Particles containing at least one top quark (t quark) are of particular interest in particle physics due to the top quark's extremely large mass and unique properties. The presence of a top quark in a particle can significantly affect its behavior and interactions. Here's an extensive overview of particle combinations with at least one top quark:
Top Quark-Antibottom Quark Mesons (Top Mesons):
Top-Antitop Quark Pair (tt̅):
In high-energy particle collisions, such as those at the Large Hadron Collider (LHC), top quark-antitop quark pairs are often produced. These events are important for studying the properties of the top quark and for probing new physics beyond the Standard Model.
Baryons with Top Quarks:
Top Quark in Exotic Particles:
Some exotic particles and pentaquarks may contain a top quark, although such particles are hypothetical and have not been observed as of my knowledge cutoff date.
W and Z Bosons from Top Quark Decays:
When a top quark decays, it often produces a W boson, which can subsequently decay into other particles, including leptons or other quarks. The charged W boson can lead to various decay channels with neutrinos, charged leptons (e.g., electrons, muons, tau leptons), and quarks. The Z boson can also be produced in some top quark decays.
Top Quark in the Higgs Boson Loop:
In quantum field theory, top quarks are involved in radiative corrections and loops, contributing to the mass and properties of the Higgs boson. The interaction between top quarks and the Higgs field is an essential component of electroweak symmetry breaking, which gives particles mass.
Search for New Physics:
The properties, decays, and interactions of top quarks are studied intensively to search for physics beyond the Standard Model, including hints of new particles and forces that may interact with top quarks in unique ways.
Figure 149 - Top-Antibottom Meson (T+ and T0)
Figure 150 - Top-Anticharm Meson (Tc+)
Figure 151 - Top-Antitop quark pair (t𝑡 ̅)
Figure 152 - Lambda-top Baryon (Λt)
Figure 153 - Xi-top Baryon (Ξt)
Figure 154 - Omega-top Baryon (Ωt)
Creation of top quarks
Quark-Antiquark Annihilation (q-qbar -> t-tbar):
This is one of the most common processes for top quark production at hadron colliders like the Large Hadron Collider (LHC). In this process, a high-energy quark and antiquark (e.g., up and anti-up) annihilate, creating a virtual W boson. The virtual W boson then decays into a top quark and a bottom quark, forming a top-antitop quark pair.
Gluon-Gluon Fusion (gg -> t-tbar):
Another significant production mode at hadron colliders is the fusion of two gluons. Gluons are the carriers of the strong nuclear force, and they can interact with each other to produce a top-antitop pair. This process involves higher-order QCD (quantum chromodynamics) corrections and is dominant at very high energies.
Associated Production (e.g., Wt and Zt):
Top quarks can also be produced in association with other particles, such as a W or Z boson. These processes are important for top quark studies and measurements at the LHC. In the case of associated production with a W or Z boson, a W or Z boson is produced along with a single top quark.
Single Top Quark Production:
Single top quarks can be produced through several channels, including t-channel, s-channel, and Wt-channel processes. These processes involve the exchange of a W boson or a virtual W boson, leading to the production of a single top quark in association with other particles.
Electroweak Production:
At higher energy lepton colliders like the International Linear Collider (ILC), top quarks can also be produced via electroweak processes, where the interaction is mediated by the exchange of electroweak bosons, such as the Z boson or photon.
Top Quark Pair Production in Lepton Colliders:
In lepton colliders like the Tevatron and the LHC, top quark-antitop quark pairs can be produced in electron-positron or proton-antiproton collisions. These experiments often produce cleaner data for top quark studies.
Top Quark Production in Rare Decay Processes:
In certain rare decay processes, top quarks can be produced. For example, in some decays of B mesons, a top quark can be created as a virtual particle before it decays into lighter particles.
Figure 158 - Electroweak production with top quark
Figure 157 - Single top quark production
Figure 156a – Associated Production
Figure 156 - Gluon-Gluon fusion
Figure 155 - Quark-Antiquark annihilation with up quark and top quark
Figure 159 - Top Quark Pair Production
Figure 160 - Top Quark Production in Rare Decay Processes
Decay of top quarks
The primary decay mode for the top quark is through the weak force via the W boson. There are two primary decay channels for top quarks:
Top Quark Decaying into a W Boson and a Bottom Quark (t → W+ b):
In this decay mode, the top quark transforms into a W+ boson and a bottom quark. This decay has a branching fraction close to 100% in the Standard Model.
The W+ boson can subsequently decay in one of three ways:
The choice of which W decay mode occurs depends on the available energy and the mixing angles of the weak interactions.
Top Quark Decaying into a W- Boson and a Strange Quark (t → W- s):
In this less common decay mode, the top quark can transform into a W- boson and a strange quark. This decay is less frequent than the primary decay mode and has a much smaller branching fraction.
Additionally, due to the short lifetime of the top quark, there are no other significant decay modes within the Standard Model. The top quark typically decays within a timescale too short to form hadrons (particles made of quarks) such as protons or mesons
Figure 161 - Decay of Top Quark into W+ Boson
Figure 162 - Top Quark Decaying into a W- Boson and a Strange Quark
Annihilation of top quarks
Annihilation processes involving top quarks are not as common as some other processes in particle physics, but they do occur in specific circumstances. The annihilation of top quarks typically involves the collision of a top quark with its antiparticle, the antitop quark (t-tbar annihilation).
Pair Annihilation (t-tbar -> X):
In this process, a top quark (t) and an antitop quark (tbar) collide and annihilate each other, resulting in the creation of other particles (X). This can happen in high-energy collisions within particle accelerators, such as the Large Hadron Collider (LHC).
The annihilation of top quarks occurs via the strong nuclear force (quantum chromodynamics or QCD) because both top and antitop quarks are colored particles. This means that they can exchange gluons, which mediate the strong force interactions.
Production of Intermediate Particles (X):
The outcome of t-tbar annihilation can produce a variety of particles as "X." The specific particles created depend on the energy of the collision and the available phase space. Common outcomes include:
Gluon Emission: One or more gluons can be emitted during the annihilation process. Gluons are massless, color-charged particles responsible for mediating the strong force.
Quark-Antiquark Pairs: The annihilation can produce quark-antiquark pairs, such as bottom quark-antibottom quark pairs, charm quark-anticharm quark pairs, or others.
W and Z Bosons: In some cases, a W or Z boson can be created as intermediate particles.
Higgs Boson: In rare instances, t-tbar annihilation can result in the creation of a Higgs boson.
Final State Particles (Decays of X):
The particles produced in the annihilation process subsequently decay into lighter particles according to the laws of particle physics. For example, a W or Z boson may decay into pairs of quarks, leptons, or neutrinos, depending on its type.
The study of the final state particles and their properties is crucial for understanding the dynamics of t-tbar annihilation and for testing the predictions of the Standard Model.
It's essential to note that top quarks have a very short lifetime, approximately 5 x 10^(-25) seconds, which means they typically decay before forming hadrons (particles made of quarks). This is why the annihilation process, in which a top quark and an antitop quark annihilate directly into other particles, is a rare occurrence. These processes are studied at high-energy particle colliders like the LHC to better understand the properties and interactions of top quarks, as well as to search for any deviations from the predictions of the Standard Model.
Figure 163 - t-tbar annihilation with gluon emission
Figure 164 - Quark-Antiquark annihilation with quark antiquark production
Figure 165 - Top quark annihilation with W and Z boson creation
Figure 166 - Top quark annihilation with Higgs boson creation
Top Quark Fusion
Se annihilation processes
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