Antibottom Quark
Composition :
Statistics :
Generation :
Family :
Interaction forces :
Symbol :
Antiparticle :
Mass :
Decays into :
Electric charge :
Color charge
Spin :
Weak isospin :
Weak hypercharge:
Elementary antiparticle
Fermionic
Third
Quark
strong, weak,
electromagnetic force
gravity
b
Bottom quark ( b )
4.18 GeV/c²
charm quark or
up quark
+¹/₃ e
Yes
¹/₂
LH : - ¹/₂, RH : 0
LH: 1/3; RH: -2/3
_
+ 0.4
- 0.3
General
The antibottom quark, often denoted as (pronounced "bar b"), is an elementary subatomic particle with several distinct characteristics:
Electric Charge: The antibottom quark has an electric charge of -1/3 elementary charges (e). This makes it negatively charged. Quarks carry fractional electric charges, in contrast to leptons (e.g., electrons) that have integral electric charges.
Mass: The antibottom quark is one of the heaviest of the six known types of quarks. Its mass is approximately 4.18 GeV/c² (gigaelectronvolts per speed of light squared). This significant mass distinguishes it from lighter quarks like up, down, and strange quarks.
Color Charge: Quarks interact via the strong nuclear force, which is described by Quantum Chromodynamics (QCD). In QCD, quarks carry a property called "color charge." However, it's important to note that this term has nothing to do with actual colors. Instead, it is a fundamental charge associated with the strong force. The antibottom quark carries an anticolor charge, which is one of three possible "anticolors."
Spin: The antibottom quark, like all quarks, has a half-integer spin of 1/2. This is a fundamental property described by quantum mechanics and is often represented as intrinsic angular momentum.
Isospin: Quarks also possess a quantum number called isospin. However, isospin is not relevant for the antibottom quark because it is not involved in the strong nuclear force. Isospin is more important for up and down quarks in the context of the weak nuclear force.
Flavor: The antibottom quark is part of the bottom flavor, which is one of the six known quark flavors. Other quark flavors include up, down, strange, charm, and top. The bottom quark and the antibottom quark are associated with the same flavor but have opposite electric charges.
Decay: Like all quarks, the antibottom quark can participate in various decay processes. These decays are governed by the weak nuclear force, electromagnetic interactions, and, in the case of antibottom quark, the strong nuclear force (QCD). It can transform into other quarks, producing a variety of hadrons (composite particles made of quarks) in the process.
Combinations with antibottom quarks
Particle combinations composed of at least one antibottom quark can be quite diverse, involving the antibottom quark ( ), as well as gluons, which mediate the strong nuclear force interactions within quantum chromodynamics (QCD). Here is an overview of some of the particle combinations involving antibottom quarks:
Mesons Containing b̅ Quark:
B-Meson:
The B- Meson is a well-known meson composed of an antibottom quark (b-) and an up quark (u). The B° meson is composed of a down quark and a antibottom quark.
Baryons Containing b̅ Quark:
Baryons containing an antibottom (b̅) quark are not commonly observed in nature due to the extreme mass of the antibottom quark. However, high-energy particle physics experiments can produce such particles. Here are a few examples of baryons containing an antibottom quark:
Tetraquarks with b̅ quarks
Some theoretical models suggest the existence of exotic tetraquark particles composed of two quarks and two antiquarks, where one of the antiquarks could be an antibottom quark. In the literature, R. J. Hudspith and R. J. Hudspith (both at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany) explain their experiment to find the Tbb tetraquark.
For Literature : See [1]
Figure 190 - B- and B°Meson
Figure 192 - Tetraquark with two antibottom quarks
Figure 191 - Baryons containg quark (Λb̅, Ξb̅ and Ωb̅)
Creation of antibottom quarks
Antibottom quarks (b̅) can be created in various high-energy processes in particle physics experiments and in the natural environment, typically involving extreme conditions. Here's an overview of the possible processes in which antibottom quarks can be created:
Collisions in Particle Accelerators:
Proton-Proton Collisions: In particle accelerators like the Large Hadron Collider (LHC), protons are accelerated to high energies and then collided. These collisions can produce antibottom quarks through the exchange of energy and momentum between the colliding protons.
Heavy Ion Collisions: Experiments involving heavy ions, such as lead or gold nuclei, can create extremely high-energy conditions. These collisions can lead to the creation of exotic particles, including antibottom quarks.
Decays of Heavier Particles:
Antibottom quarks can be produced as decay products when heavier particles containing bottom quarks (b) decay. For example, bottom mesons (B mesons) can decay into lighter particles, and this process can lead to the creation of antibottom quarks.
Cosmic Ray Interactions:
In the upper atmosphere, high-energy cosmic rays, which are typically protons and other atomic nuclei from space, interact with atoms in the Earth's atmosphere. These interactions can produce a cascade of secondary particles, including antibottom quarks, as a result of the high-energy collisions.
High-Energy Astrophysical Phenomena:
In extreme astrophysical environments, such as supernovae, gamma-ray bursts, or the core of neutron stars, conditions can become so energetic that they can lead to the creation of particles like antibottom quarks.
Lattice QCD Calculations:
In theoretical calculations within the framework of lattice quantum chromodynamics (Lattice QCD), researchers simulate the behavior of quarks and gluons within the strong force. These simulations can predict the creation and behavior of antibottom quarks in various high-energy interactions.
Experiments to Search for Rare Particles:
Some particle physics experiments are specifically designed to search for rare or exotic particles. These experiments may involve specialized detectors and conditions optimized for the creation and detection of particles like antibottom quarks.
It's important to note that antibottom quarks are highly unstable and have a very short lifetime. When created, they quickly decay into other particles, primarily through weak force interactions. The specific decay modes and products depend on the circumstances of their creation and the energy involved.
Figure 192a – Collisions in particle accelerators creating top quark
Decay of antibottom quarks
Antibottom quarks (b̅) are unstable elementary particles, and they undergo decay processes primarily through weak force interactions. The specific decay modes and products depend on the circumstances and energy of the interactions. Here is a detailed description of the possible decay processes of an antibottom quark:
Semileptonic Decay
In this decay process, an antibottom quark (b̅) transforms into a charm antiquark (c̅) through the exchange of a charged W- boson.
The W- boson decays into a lepton (e, μ, or τ) and a corresponding neutrino (νe, νμ, or ντ). For example, if the W- decays into an electron and an electron neutrino, the process is represented as b̅ → c̅eνe.
The electron or another lepton carries away energy and momentum, making the observation of this decay mode in experiments feasible.
The charm antiquark (c̅) can subsequently participate in other weak decays or form mesons or hadrons.
Hadronic Decay
B-Meson decays
Radiative Decay (b̅ → c̅γ):
In rare cases, an antibottom quark (b̅) can undergo radiative decay, where it transforms into a charm antiquark (c̅) and emits a photon (γ).
The emission of the photon carries away energy, and this process is relatively rare compared to other decay modes.
The emitted photon can be detected in experiments, contributing to the identification of this decay mode.
Flavor-Changing Neutral Current (FCNC) Decays:
In the Standard Model of particle physics, some antibottom quark decays can occur through flavor-changing neutral current processes, which involve the exchange of neutral gauge bosons (Z0).
An example of such a process is b̅ → s̅γ, where the antibottom quark transforms into a strange antiquark (s̅) and emits a photon (γ).
FCNC processes are typically rare and are sensitive probes for testing the Standard Model.
Lepton Flavor Violation (LFV):
In some theoretical extensions of the Standard Model, antibottom quarks could participate in processes involving lepton flavor violation. This would result in the creation of unusual final states, such as muons or tau leptons in the decay products.
Figure 193 - Semileptonic b̅ decay
Figure 195 - B+ Meson Decay
Figure 194 - Sample real-radiation diagram embedding the hadronic decay of an antitop quark
Figure 196 - B°s Decay
Figure 198 - FCNC decay of an antibottom
Figure 197 - Radiative decay of the ϒ Vector Meson
Annihilation of antibottom quarks
See previous chapter “Annihilation of bottom quarks”
Fusion of antibottom quarks
Bottom-antibottom quark fusion, or the annihilation of a bottom quark and an antibottom quark, can result in the creation of several different types of particles and phenomena, depending on the energy of the collision and other factors. The specific outcome is governed by the conservation laws of energy, momentum, electric charge, and other quantum numbers. Some possible outcomes include:
Gluon Emission: The strong force between quarks is mediated by particles called gluons. During bottom-antibottom quark annihilation, gluons may be radiated, carrying away energy and momentum. These emitted gluons can then interact with other quarks or gluons, leading to the creation of quark-antiquark pairs or the production of additional hadrons.
Heavy Meson Production: Bottom-antibottom quark fusion can lead to the creation of heavy mesons, such as B mesons, which consist of a bottom quark and an antibottom quark. These heavy mesons are unstable and eventually decay into other particles.
Lepton Production: Under specific conditions, bottom-antibottom quark annihilation can result in the creation of lepton-antilepton pairs. This occurs through the exchange of intermediate bosons like W and Z bosons, which then decay into leptons, such as electrons, positrons, muons, or antimuons.
Photon Emission: In some cases, if the energy of the annihilation is high enough, it can lead to the production of photons (gamma rays). This is essentially the conversion of the quark-antiquark pair's energy into electromagnetic radiation, as described by Einstein's famous equation, E=mc².
The exact outcome of a bottom-antibottom quark fusion event depends on the energy and the specific circumstances of the collision. High-energy experiments at particle accelerators like the Large Hadron Collider (LHC) are designed to study such processes in order to understand the fundamental interactions and particles involved in these high-energy collisions.
References
[1] Exotic tetraquark states with two ¯ b quarks and JP = 0 + and 1 + Bs states in a nonperturbatively tuned lattice NRQCD setup. R. J. Hudspith and D. Mohler (GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany). PHYSICAL REVIEW D 107, 114510 (2023)
[2] Electroweak and QCD corrections to off-shell single-top production in association with a Z boson at the LHC. Giovanni Pelliccioli (Max-Planck-Institut für Physik, München, Germany), Proceedings of Science PoS(RADCOR2023)037
[3] Electroweak and QCD corrections to off-shell single-top production in association with a Z boson at the LHC. Giovanni Pelliccioli (Max-Planck-Institut für Physik, München, Germany), Proceedings of Science PoS(RADCOR2023)037