Search results for "weak interaction"
showing 10 items of 431 documents
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).
Weak-interaction and nuclear-structure aspects of nuclear double beta decay
1998
Abstract Weak-interaction and nuclear-structure aspects of double beta decay are reviewed. Starting from effective electroweak lagrangians, decay rates for the two-neutrino and neutrinoless modes of the nuclear double beta decay transitions are defined and second-order perturbative expressions for the nuclear decay amplitudes are given. Nuclear matrix elements of the relevant operators are presented, as extracted from data and from shell-model and QRPA calculations as well as from other theoretical approximations. The analysis is performed both for the two-neutrino and neutrinoless modes of the decay. The expressions for ground-state-to-ground-state and ground-state-to-excited-state transit…
Electroweak effects in the extraction of the CKM angle γ from B→Dπ decays
2015
The angle γ of the standard CKM unitarity triangle can be determined from tree-level B-meson decays essentially without hadronic uncertainties. We calculate the second-order electroweak corrections for the B→Dπ modes and show that their impact on the determination of γ could be enhanced by an accidental cancellation of poorly known hadronic matrix elements. However, we do not expect the resulting shift in γ to exceed |δγDπ/γ|≲O(10−4).
Elements of Quantum Electrodynamics and Weak Interactions
2013
Quantum field theory in its application to electroweak and strong interactions has two rather different facets: A pragmatic, empirical one, and an algebraic, systematical one. The pragmatic approach consists in a set of rules and formal calculational procedures which are extremely successful in their application to concrete physical processes, but rest on mathematically shaky ground. The mathematically rigorous approach, in turn, is technically difficult and not very useful, from a practical point of view, for reaching results which can be compared with phenomenology. Generally speaking, quantum field theory quickly becomes rather technical if one wants to understand it in some depth, and g…
QEC value of the superallowed β emitter Sc42
2017
Precise measurements of superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ $\ensuremath{\beta}$ decay presently provide the most precise value for the weak mixing amplitude ${V}_{u\phantom{\rule{0}{0ex}}d}$. As the largest element of the CKM matrix, ${V}_{u\phantom{\rule{0}{0ex}}d}$ is a critical piece of the Standard Model of the electroweak interaction. The new, precise Penning-trap mass measurement of the decay energy for the superallowed transition in ${}^{42}$Sc opens the door for a much more precise $f\phantom{\rule{0}{0ex}}t$ value determination if its half-life can be measured more precisely as well.
Progress and open questions in the physics of neutrino cross sections at intermediate energies
2014
New and more precise measurements of neutrino cross sections have renewed the interest in a better understanding of electroweak interactions on nucleons and nuclei. This effort is crucial to achieve the precision goals of the neutrino oscillation program, making new discoveries, like the CP violation in the leptonic sector, possible. We review the recent progress in the physics of neutrino cross sections, putting emphasis on the open questions that arise in the comparison with new experimental data. Following an overview of recent neutrino experiments and future plans, we present some details about the theoretical development in the description of (anti)neutrino-induced quasielastic scatter…
Consistency of the dynamical high-scale type-I seesaw mechanism
2019
We analyze the consistency of electroweak breaking within the simplest high-scale Standard Model type-I seesaw mechanism. We derive the full two-loop RGEs of the relevant parameters, including the quartic Higgs self-coupling of the Standard Model. For the simplest case of bare "right-handed" neutrino mass terms we find that, with large Yukawa couplings, the Higgs quartic self-coupling becomes negative much below the seesaw scale, so that the model may be inconsistent even as an effective theory. We show, however, that the "dynamical" type-I high-scale seesaw with spontaneous lepton number violation has better stability properties.