Z°-boson

It led to a prediction that the number of different sorts of neutrino (equivalent in standard particle physics to the number of families of quarks and leptons) is less than 4 and probably no more than 3. This prediction was subsequently confirmed (subject to slight reservations about differences between effective numbers of neutrino species in the laboratory and in the early Universe) by measurements of the width or lifetime of the Z° boson at CERN in 1990. 

The weak interaction contribution to the Lamb shift is generated by the Z-boson exchange in Fig. 6.7, which may be described by the effective local low-energy Hamiltonian... 

The weak interaction contribution to hyperfine splitting is due to Z-boson exchange between the electron and muon in Fig. 6.7. Due to the large mass of the Z-boson this exchange is effectively described by the local four-fermion interaction Hamiltonian... 

The prediction of a heavy boson has received preliminary empirical support [92,96] from an anomaly in Z decay widths that points toward the existence of Z bosons with a mass of 812 GeV 1 33j [92,96] within the SO(l) grand unified field model, and a Higgs mechanism of 145 GeV4gj3. This suggests that a new massive neutral boson has been detected. Analysis of the hadronic peak cross sections obtained at LEP [96] implies a small amount of missing invisible width in Z decays. The effective number of massless neutrinos is 2.985 0.008, which is below the prediction of 3 by the standard model of electroweak interactions. The weak charge Qw in atomic parity violation can be interpreted as a measurement of the S parameter. This indicates a new Qw = 72.06 0.44, which is found to be above the standard model pre-... 

Brown, L.M., M Dresden, and L. Hoddeson From Pions to Quarks Particle Ph)>sics in the 1950s, Cambridge University Press, New York, NY, 1989. Chanowitz, M.S. The Z Boson, Science, 36 (July 6. 1990). 

Neutrinos can be cold dark matter if their masses are around few GeV or a TeV. However, fourth-generation heavy neutrinos lighter than 45 GeV are excluded by the measurement of the Z-boson decay width at the Large Electron-Positron collider at CERN. Moreover, direct searches for WIMP dark matter in our galaxy exclude Dirac neutrinos heavier than 0.5 GeV as the dominant component of the galactic dark halo (see Figure 3). Thus although heavy Dirac neutrinos could still be a tiny part of the halo dark matter, they cannot solve the cold dark matter problem. 

The dominant interaction within the muonium atom is electromagnetic. This can be treated most accurately within the framework of bound state Quantum Electrodynamics (QED). There are also contributions from weak interaction which arise from Z°-boson exchange and from strong interaction due to vacuum polarization loops with hadronic content. Standard theory, which encompasses all these forces, allows to calculate the level energies of muonium to the required level of accuracy for all modern precision experiments1. 

Particles with integer spin have symmetric wave function and are called bosons, in contrast to fermions they share same quantrun states. Examples of bosons include the photon and the W and Z bosons. 

Elbaz and Meyer 12°) have proposed a bootstrap topological approach to both quarks and leptons, where the T and V rishons are vectors in a space having the observable particles as scalars. Also the W and Z bosons can be included. These authors attempt to derive Pauli s exclusion principle for fermions from the properties of rishons. 

The well-known proton, neutron, and electron are now thought to be members of a group that includes other fundamental particles that have been discovered or hypothesized by physicists. These very elemental particles, of which all matter is made, are now thought to belong to one of two families namely, quarks or leptons. Each of these two families consists of six particles. Also, there are four different force carriers that lead to interactions between particles. The six members or flavors of the quark family are called up, charm, top, down, strange, and bottom. The force carriers for the quarks are the gluon and the photon. The six members of the lepton family are the e neutrino, the mu neutrino, the tau neutrino, the electron, the muon particle, and the tau particle. The force carriers for these are the w boson and the z boson. Furthermore, it appears that each of these particles has an anti-particle that has an opposite electrical charge from the above particles. 

Based on the ratio of the masses of the W and Z bosons rmnlinz recommended by the Particle Data Group (Yao et al., 2006). The value for they recommend, which is based on a particular variant of the modified minimal subtraction (MS) scheme, is sin (Mz) = 0.231 22(15). 

Here j is the electromagnetic four-current, and j are weak charged currents and finally j° is the weak neutral current that couples to the Z° boson. This neutral current deserves our particular attention when we are interested in molecular parity violating effects. 

In recent years a search has been made for a hypothetical particle known as the Hi s particle or Higgs boson, suggested in 1966 by Peter Higgs of the University of Edinburgh, which could possibly explain why the carriers of the electro-weak field (w and z bosons) have mass. The Higgs particle is thought to be responsible possibly for the mass of objects throughout the universe. 

For weak interactions the force is mediated by three particles called W+, W , and Z° bosons for the strong force it is the gluon. Current theories of quantum gravity propose the graviton as the mediator tor the graMta-tional interaction, but this work is highly... 

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