The search for anomalous couplings is one of the possible ways to find any deviations from the Standard Model. Effective field theory is used to parameterize the anomalous couplings in the Lagrangian ...with operators of higher dimensions constructed from the SM fields. In the classical way, the limits on the Wilson coefficients of these operators are set based on beyond the Standard Model contributions induced for the signal process, whereas the ones induced for background processes are assumed to be negligible. This article provides a study of the corrections to the limits on Wilson coefficients by considering beyond the Standard Model contributions induced for background processes. The studies of Z(νν¯)γjj and W(ℓν)γjj productions in pp collisions with s=13 TeV and conditions of the ATLAS experiment at the LHC are used as an example. Cases with integrated luminosity collected during Run II of 139 fb−1 and expected from Run III of 300 fb−1 are considered. The expected 95% CL limits on coefficients fT0/Λ4, fT5/Λ4, fM0/Λ4 and fM2/Λ4 are obtained both in the classical way and in the way, where the corrections from background anomalous contributions are applied. Corrected one-dimensional limits from Z(νν¯)γjj and W(ℓν)γjj productions are up to 9.1% and 4.4% (depending on the operator) tighter than the classical ones, respectively. Corrected combined limits are up to 3.0% (depending on the operator) tighter than the classical ones. Corrections to two-dimensional limits are also obtained. The corrected contours are more stringent compared with the classical ones, and the maximal improvement is 17.2%.
PHASE—an event generator for six fermion physics at the LHC Accomando, E.; Ballestrero, A.; Maina, E.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2004, Volume:
534, Issue:
1
Journal Article
Peer reviewed
Open access
PHASE is a Monte Carlo event generator, under construction, for all Standard Model processes with six fermions in the final state at the LHC. It employs the full set of tree level Feynman diagrams, ...taking into account fermion masses for b quarks. The program can generate unweighted events for any subset of all six-fermion final states in a single run, by making use of dedicated pre-samples. An interface to hadronization is provided.
In the absence of a light Higgs boson, the mechanism of electroweak symmetry breaking will be best studied in processes of vector boson scattering at high mass. Various models predict resonances in ...this channel. Scalar and vector resonances have been investigated in the WW, WZ and ZZ channels. The ability of ATLAS to measure the di-boson cross-section over a range of centre-of-mass energies has been studied with particular attention paid to the reconstruction of jet pairs with low opening angle resulting from the decays of highly boosted vector bosons.
This Letter reports measurements of differential cross sections for the production of two Z bosons in association with jets in proton-proton collisions at $\sqrt{s} =$ 8 and 13 TeV. The analysis is ...based on data samples collected at the LHC with the CMS detector, corresponding to integrated luminosities of 19.7 and 35.9 fb$^{-1}$ at 8 and 13 TeV, respectively. The measurements are performed in the leptonic decay modes ZZ$\to\ell^+ \ell^- \ell'^+ \ell'^-$, where $\ell,\ell' =$ e, $\mu$. The differential cross sections as a function of the jet multiplicity, the transverse momentum $p_\mathrm{T}$, and pseudorapidity of the $p_\mathrm{T}$-leading and subleading jets are presented. In addition, the differential cross sections as a function of variables sensitive to the vector boson scattering, such as the invariant mass of the two $p_\mathrm{T}$-leading jets and their pseudorapidity separation, are reported. The results are compared to theoretical predictions and found in good agreement within the theoretical and experimental uncertainties.
A measurement of WZ electroweak (EW) vector boson scattering is presented. The measurement is performed in the leptonic decay modes WZ$\to \ell\nu\ell'\ell'$, where $\ell, \ell' = $e, $\mu$. The ...analysis is based on a data sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV at the LHC collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The WZ plus two jet production cross section is measured in fiducial regions with enhanced contributions from EW production and found to be consistent with standard model predictions. The EW WZ production in association with two jets is measured with an observed (expected) significance of 2.2 (2.5) standard deviations. Constraints on charged Higgs boson production and on anomalous quartic gauge couplings in terms of dimension-eight effective field theory operators are also presented.
The production of a $Z$ boson and a photon in association with a high-mass dijet system is studied using 20.2fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV ...recorded with the ATLAS detector in 2012 at the Large Hadron Collider. Final states with a photon and a Z boson decaying into a pair of either electrons, muons, or neutrinos are analysed. Electroweak and total $pp \to Z\gamma j j$ cross-sections are extracted in two fiducial regions with different sensitivities to electroweak production processes. Quartic couplings of vector bosons are studied in regions of phase space with an enhanced contribution from pure electroweak production, sensitive to vector-boson scattering processes $VV \to Z\gamma$. No deviations from Standard Model predictions are observed and constraints are placed on anomalous couplings parameterized by higher-dimensional operators using effective field theory.
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