Search results for "Electroweak interaction"
showing 10 items of 358 documents
Primakoff scattering for polarized photons or polarized protons
1993
Abstract We present a way to measure the axial coupling of the proton for the neutral strangeness current in coherent π0 production induced by photon-proton scattering. By means of the γ−Z−π0 triangle anomaly, the parity violating asymmetries for polarized photon or polarized proton Primakoff effect filter the couplings so as to leave the proton axial coupling only. We calculate the relevant observables induced by the electroweak interference and give results for regions of energy and Q2 of possible experimental interest. The polarized proton asymmetry is predicted to be 10−6-10−5 when Q2 ∼ 0.1−0.5 GeV2.
Tests of the Standard Model with Low-Energy Neutrino Beams
2007
We discuss the possibility of using future high--intensity low--energy neutrino beams for precision tests of the Standard Model. In particular we consider the determination of the electroweak mixing angle from elastic and quasi--elastic neutrino--nucleon scattering at a superbeam or $\beta$--beam.
ELECTROWEAK THEORY AND THE NEUTRINO-MASS AND NEUTRINO-OSCILLATION QUESTIONS
2007
It is shown that both conjectures of neutrino mass and neutrino oscillation can be made really well-grounded within the Standard Model provided that one adopts a recent new version of the electroweak scheme spontaneously giving also a fundamental explanation for the so-called "maximal parity-violation" effect. A crucial role is played by the prediction of two distinct, scalar and pseudoscalar, replicas of (electron, muon, and tau) lepton numbers that could fully account for an actual non-coincidence between neutrino mass-eigenstates and gauge-eigenstates.
Weak magnetic dipole moments in two-Higgs-doublet models
1995
We investigate the effects of the new scalars in a two-Higgs-doublet model on the weak magnetic dipole moments of the fermions at the $Z$ peak. Proportionality of the Yukawa couplings to the fermion masses, and to $\tan{\beta}$, makes such effects more important for the third family, and potentially relevant. For the $\tau$ lepton, the new diagrams are suppressed by $v_\tau = 2 \sin^2 \theta_W - 1/2$, or by powers of $m_\tau/M_Z$, but may still be comparable to the SM electroweak contributions. In contrast, we find that the new contributions for the bottom quark may be much larger than the SM electroweak contributions. These new effects may even compete with the gluonic contribution, if the…
Limits on Anomalous Top Couplings from Z Pole Physics
1997
We obtain constraints on possible anomalous interactions of the top quark with the electroweak vector bosons arising from the precision measurements at the Z pole. In the framework of $SU(2)_L \otimes U(1)_Y$ chiral Lagrangians, we examine all effective CP-conserving operators of dimension five which induce fermionic currents involving the top quark. We constrain the magnitudes of these anomalous interactions by evaluating their one-loop contributions to the Z pole physics. Our analysis shows that the operators that contribute to the LEP observables get bounds close to the theoretical expectation for their anomalous couplings. We also show that those which break the $SU(2)_C$ custodial symm…
Status and Prospects of Top-Quark Physics
2009
The top quark is the heaviest elementary particle observed to date. Its large mass of about 173 GeV/c^2 makes the top quark act differently than other elementary fermions, as it decays before it hadronises, passing its spin information on to its decay products. In addition, the top quark plays an important role in higher-order loop corrections to standard model processes, which makes the top quark mass a crucial parameter for precision tests of the electroweak theory. The top quark is also a powerful probe for new phenomena beyond the standard model. During the time of discovery at the Tevatron in 1995 only a few properties of the top quark could be measured. In recent years, since the star…
Electroweak Precision Tests of the Standard Model after the Discovery of the Higgs Boson
2019
The global fit of the Standard Model predictions to electroweak precision data, which has been routinely performed in the past decades by several groups, led to the prediction of the top quark and the Higgs boson masses before their respective discoveries. With the measurement of the Higgs boson mass at the Large Hadron Collider (LHC) in 2012 by the ATLAS and CMS collaborations, the last free parameter of the Standard Model of particle physics has been fixed, and the global electroweak fit can be used to test the full internal consistency of the electroweak sector of the Standard Model and constrain models beyond. In this article, we review the current state-of-the-art theoretical calculati…
Experimental results on the electroweak interaction
1999
Recent results from the four experiments ALEPH, DELPHI, L3 and OPAL at the Large Electron-Positron collider, LEP at CERN, and by the SLD collaboration at the Stanford Linear Collider, SLC, are reviewed. Analyses from an integrated luminosity of about 150 pb− recorded by each experiment at LEP, taken at different centre-of-mass energies within ±3 GeV around the peak of the Z resonance during the years 1989 to 1995 are available now. Repeated accurate calibrations of the beam energy lead to precise measurements of the mass and of the total width of the Z boson. These results are complemented by measurements at the Z resonance with polarised beams at Stanford. First results from an integrated …
Top quark decay in the Aligned two-Higgs-doublet Model
2015
AbstractWe compute the one loop right and left anomalous tensor couplings (gR and gL, respectively) for the top quark, in the aligned two-Higgs-doublet model. They are the magnetic-like couplings in the most general parameterization of the tbW vertex. We find that the aligned two-Higgs doublet model, that includes as particular cases some of the most studied extensions of the Higgs sector, as Type I and II 2HDM, introduces new electroweak contributions and provides theoretical predictions that are very sensitive to both new scalar masses and the neutral scalar mixing angle. The model can account for new CP violation effects via the introduction of complex alignment parameters that have impo…
Combination of searches for anomalous top quark couplings with 5.4 fb−1 of pp¯ collisions
2012
We present measurements of the tWb coupling form factors using information from electroweak single top quark production and from the helicity of W bosons from top quark decays in t (t) over bar events. We set upper limits on anomalous tWb coupling form factors using data collected with the DO detector at the Tevatron p (p) over bar collider corresponding to an integrated luminosity of 5.4 fb(-1).