Search results for " Standard Model"
showing 10 items of 645 documents
Old and new physics interpretations of the NuTeV anomaly
2001
We discuss whether the NuTeV anomaly can be explained, compatibly with all other data, by QCD effects (maybe, if the strange sea is asymmetric, or there is a tiny violation of isospin), new physics in propagators or couplings of the vector bosons (not really), loops of supersymmetric particles (no), dimension six operators (yes, for one specific SU(2)-invariant operator), leptoquarks (not in a minimal way), extra U(1) gauge bosons (maybe: an unmixed Z' coupled to B-3L_mu also increases the muon g-2 by about 10^{-9} and gives a `burst' to cosmic rays above the GZK cutoff).
Precision Tau Physics
2013
Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of tau physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the tau lepton probe the structure of the weak currents and the universality of their couplings to the W boson. The universality of the leptonic Z couplings has also been tested through leptonic Z decays. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the C…
Tau physics: theoretical perspective
2001
12 páginas, 10 figuras, 3 tablas.-- Comunicación presentada al 6º International Workshop on Tau Lepton Physics celebrado del 18 al 21 de Septiembre de 2000 en Victoria (Canada).-- arXiv:hep-ph/0012297v1
The importance of being rigid: D6-brane model building on with discrete torsion
2013
Model building with rigid D6-branes on the Type IIA orientifold onT 6 =Z2 Z 0 with discrete torsion is considered. The systematic search for models of particle physics is signicantly reduced by proving new symmetries among dierent lattice orientations. Suitable rigid D6-branes without matter in adjoint and symmetric representations are classied, and SO(2N) and USp(2N) gauge factors on orientifold invariant D6-branes are distinguished in terms of their discrete Wilson line and displacement parameters. Constraints on the nonexistence of exotic matter prohibit global completions of local MSSM and leftright symmetric models, while globally dened supersymmetric Pati-Salam models are found. For t…
Novel nonperturbative approach for radiativeB¯0(B¯s0)→J/ψγdecays
2016
Radiative ${\overline{B}}^{0}({\overline{B}}_{s}^{0})\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma}$ decays provide an interesting case to test our understanding of (non)perturbative QCD and eventually to probe physics beyond the standard model. Recently, the LHCb Collaboration reported an upper bound, updating the results of the BABAR Collaboration. Previous theoretical predictions based on QCD factorization or perturbative QCD have shown large variations due to different treatment of nonfactorizable contributions and meson-photon transitions. In this paper, we report on a novel approach to estimate the decay rates, which is based on a recently proposed model for $B$ decays…
WZ Production in Association with Two Jets at Next-to-Leading Order in QCD
2013
We report on the calculation of W-+/- Zjj production with leptonic decays at hadron-hadron colliders at next-to-leading order in QCD. These processes are important both to test the quartic gauge couplings of the standard model and because they constitute relevant backgrounds to beyond standard model physics searches. Our results show that the next-to-leading order corrections reduce significantly the scale uncertainties and have a nontrivial phase space dependence.
Symmetries in the angular distribution of exclusive semileptonic B decays
2010
We discuss a method to construct observables protected against QCD uncertainties based on the angular distribution of the exclusive Bd -> K(*0}(-> Kpi) l+ l- decay. We focus on the identification and the interpretation of all the symmetries of the distribution. They constitute a key ingredient to construct a set of so-called transverse observables. We work in the framework of QCD factorization at NLO supplemented by an estimate of power-suppressed Lambda/mb corrections. A discussion of the new physics properties of two of the transverse asymmetries, AT^{(2)} and AT^{(5)}, is presented. A comparison between the transverse asymmetry AT^{(2)} and the forward-backward asymmetry shows that…
W+W− production at high transverse momenta beyond NLO
2014
Pair production of W gauge bosons is an important process at the LHC entering many experimental analyses, both as background in new-physics searches or Higgs measurements and as signal in precision studies and tests of the Standard Model. Therefore, accurate predictions for this class of processes are of great interest in order to exploit the full potential of LHC measurements. We use the LoopSim method to combine NLO QCD results for WW and WW + jet, as well as the loop-squared gluon-fusion contribution, to obtain approximate NNLO predictions for WW production. The cross sections are calculated with VBFNLO and include leptonic decays of the W bosons as well as finite-width and off-shell eff…
Measurement of the Soft-Drop Jet Mass in pp Collisions at s=13 TeV with the ATLAS Detector
2018
Jet substructure observables have significantly extended the search program for physics beyond the standard model at the Large Hadron Collider. The state-of-the-art tools have been motivated by the ...
Measurements of Higgs boson properties in the diphoton decay channel with 36 fb−1 of pp collision data at s=13 TeV with the ATLAS detector
2018
Properties of the Higgs boson are measured in the two-photon final state using 36.1 fb-1 of proton? proton collision data recorded at ffiffi √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vectorboson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of 0.99 ± 0.14 improves on the precision of the ATLAS measurement at √s = 7 and 8 TeV by a factor of two. …