Rightarrow ZZ Research Articles

Physics potential for the Hrightarrow hbox {ZZ}^{*} decay at the CEPC

The precision of the yield measurement of the Higgs boson decaying into a pair of Z bosons process at the Circular Electron Positron Collider is evaluated. Including the recoil Z boson associated with the Higgs production (Higgsstrahlung) a total of three Z bosons are involved for this channel, from which final states characterized by the presence of a pair of leptons, quarks, and neutrinos are chosen for the signal. Two analysis approaches are compared and the final statistical precision of {sigma }_{mathrm {ZH}}{cdot }BR(H rightarrow ZZ^{*}) is estimated to be 6.9% using a multivariate analysis technique, based on boosted decision trees. The relative precision of the Higgs boson width, using this H rightarrow ZZ^{*} decay topology, is estimated by combining the obtained result with the precision of the inclusive ZH cross section measurement.

Four-lepton production in gluon fusion at NLO matched to parton showers

We present a calculation of the next-to-leading order (NLO) QCD corrections to gluon-induced electroweak gauge boson pair production, gg rightarrow ZZ and gg rightarrow W^+W^-, matched to the PYTHIA 8 parton shower in the POWHEG approach. The calculation consistently incorporates the continuum background, the Higgs-mediated ggrightarrow H^* rightarrow VV process, and their interference. We consider leptonic decay modes of the vector bosons and retain offshell and non-resonant contributions. The processes considered are loop-induced at leading order and thus contain two-loop virtual contributions as well as loop-squared real contributions. Parton-shower effects are found to be marginal in inclusive observables and quite sizeable in observables that are exclusive in additional jet radiation. The Monte Carlo generator presented here allows for realistic experimental effects to be incorporated in state-of-the-art precision analyses of diboson production and of the Higgs boson in the offshell regime.

Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4ell decay channel at sqrt{s} = 13 TeV

Inclusive and differential fiducial cross sections of the Higgs boson are measured in the H rightarrow ZZ^{*} rightarrow 4ell (ell = e,mu ) decay channel. The results are based on proton-proton collision data produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, equivalent to an integrated luminosity of 139 hbox {fb}^{-1}. The inclusive fiducial cross section for the H rightarrow ZZ^{*} rightarrow 4ell process is measured to be sigma _mathrm {fid} = 3.28 ,{pm }, 0.32 fb, in agreement with the Standard Model prediction of sigma _mathrm {fid, SM} = 3.41 pm 0.18 fb. Differential fiducial cross sections are measured for a variety of observables which are sensitive to the production and decay of the Higgs boson. All measurements are in agreement with the Standard Model predictions. The results are used to constrain anomalous Higgs boson interactions with Standard Model particles.

Sensitivity on anomalous neutral triple gauge couplings via ZZ production at FCC-hh

We study the sensitivity of anomalous neutral triple gauge couplings (aNTGC) via pp rightarrow ZZ production in the 4ell channel at 100 TeV center of mass energy of future circular hadron collider, FCC-hh. The analysis including the realistic detector effects is performed in the mode where both Z bosons decay into same-flavor, oppositely charged lepton pairs. The sensitivities to the charge–parity (CP)-conserving couplings C_{{tilde{B}}W} / Lambda ^{4} and CP-violating couplings C_{WW} / Lambda ^{4}, C_{BW} / Lambda ^{4} and C_{BB} / Lambda ^{4} obtained at 95% Confidence Level using the invariant mass distribution of the 4ell system reconstructing the leading and sub-leading Z boson candidates are [-,0.09, ,, +,0.09], [-,0.21, ,, +,0.21], [-,0.26, ,, +,0.26], and [-,0.10, ,, +,0.10] in units of hbox {TeV}^{-4}, respectively.

Study of Majorana fermionic dark matter

We construct a generic model of Majorana fermionic dark matter (DM). Starting with two Weyl spinor multiplets $\eta_{1,2}\sim (I,\mp Y)$ coupled to the Standard Model (SM) Higgs, six additional Weyl spinor multiplets with $(I\pm 1/2, \pm(Y\pm 1/2))$ are needed in general. It has 13 parameters in total, five mass parameters and eight Yukawa couplings. The DM sector of the minimal supersymmetric standard model (MSSM) is a special case of the model with $(I,Y)=(1/2,1/2)$. Therefore, this model can be viewed as an extension of the neutralino DM sector. We consider three typical cases: the neutralino-like, the reduced and the extended cases. For each case, we survey the DM mass $m_\chi$ in the range of $(1,2500)$ GeV by random sampling from the model parameter space and study the constraints from the observed DM relic density, the direct search of LUX, XENON100 and PICO experiments, and the indirect search of Fermi-LAT data. We investigate the interplay of these constraints and the differences among these cases. It is found that the direct detection of spin-independent DM scattering off nuclei and the indirect detection of DM annihilation to $W^+W^-$ channel are more sensitive to the DM searches in the near future. The allowed mass for finding $\tilde H$-, $\tilde B$-, $\tilde W$- and non neutralino-like DM particles and the predictions on $\langle\sigma (\chi{\chi}\rightarrow ZZ, ZH, t{\bar t}) v\rangle$ in the indirect search are given.

Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector.

Studies of the spin, parity and tensor couplings of the Higgs boson in the H rightarrow ZZ^{*} rightarrow 4 ell , H rightarrow WW^{*} rightarrow e nu mu nu and H rightarrow gamma gamma decay processes at the LHC are presented. The investigations are based on 25;mathrm{fb}^{-1} of pp collision data collected by the ATLAS experiment at sqrt{s}=7 TeV and sqrt{s}=8 TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers J^{P}=0^{+}, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the H rightarrow ZZ^{*} rightarrow 4 ell and H rightarrow WW^{*} rightarrow e nu mu nu decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.

The LHC Excess of Four-lepton Events Interpreted as Higgs-boson Signal: Background from Double Drell--Yan Process?

We construct a simple model of the Double Drell--Yan Process (DDYP) for proton--proton collisions and investigate its possible contribution to the background for the Higgs-boson searches at the LHC. We demonstrate that under the assumption of the predominance of short range, ${\cal O}(0.1)\,$fm, transverse-plane correlations of quark--antiquark pairs within the proton this contribution becomes important and may even explain the observed excess of the four-lepton events at the LHC -- the events interpreted as originating from the Higgs-boson decays: $ H \rightarrow ZZ^{*} \rightarrow 4l$ and $ H \rightarrow WW^{*} \rightarrow 2l 2 \nu$.

Search for Standard Model Higgs boson in the decay channel ${\bf \textit{H}}\rightarrow {\bf \textit{ZZ}}\rightarrow {\bf \textit{l}}^{{\bf +}}{\bf \textit{l}}^{{\bf -}} q\boldsymbol{\bar{q}}$ at CMS

A search for the Standard Model Higgs boson decaying to two Z bosons with a subsequent decay to a final state with two leptons and two quark jets, \(H\rightarrow ZZ\rightarrow l^{+}l^{-} q\bar{q}\), is presented. Data corresponding to an integrated luminosity of 1.6 fb − 1 of LHC proton–proton collisions at the centre-of-mass energy of 7 TeV were collected and analysed by the CMS experiment. The selection to discriminate between signal and background events is based on kinematic and topological quantities, which include the angular spin correlations of the decay products. The events are classified according to the probability of the jets to originate from quarks of light or heavy flavour or from gluons. No evidence for a Higgs boson is found and upper limits on the Higgs boson production cross-section are set in the range of masses between 226 and 600 GeV/c2.

Radiative corrections to the Higgs-boson decay rate Gamma (H-->ZZ) in the minimal supersymmetric model.

We consider radiative corrections to the decay rate $\Gamma(H\rightarrow ZZ)$ of the heavy {\it CP}-even Higgs boson of the minimal supersymmetric model to two $Z$ bosons. We perform a one loop Feynman diagram calculation in the on-mass-shell renormalization scheme, and include the third generation of quarks and squarks. The tree level rate is suppressed by a mixing angle factor and decreases as $1/M_H$ for large $M_H$. The corrected rate overcomes this suppression and increases with $M_H$ for $M_H > 500$~GeV. The corrections can be very large and depend in detail on the top squark masses and $A$-term, as well as the supersymmetric Higgs mass parameter $\mu$.