ZZ Pairs Research Articles

Polarized ZZ pairs in gluon fusion and vector boson fusion at the LHC

Pair production of helicity-polarized weak bosons (Vλ=Wλ±,Zλ) from gluon fusion (gg→VλVλ′′) and weak boson fusion (V1V2→VλVλ′′) are powerful probes of the Standard Model, new physics, and properties of quantum systems. Measuring cross sections of polarized processes is a chief objective of the Large Hadron Collider's (LHC) Run 3 and high luminosity programs, but progress is limited by the simulation tools that are presently available. We propose a method for computing polarized cross sections that works by directly modifying Feynman rules instead of (squared) amplitudes. The method is applicable to loop-induced processes, and can capture the interference between arbitrary polarization configurations, interference with non-resonant diagrams, as well as off-shell/finite-width effects. By construction, previous results that work at the (squared) amplitude level are recoverable. As a demonstration, we report the prospect of observing and studying polarized ZλZλ′ pairs when produced via gluon fusion and electroweak processes in final-states with four charged leptons at the LHC, using the new method to simulate the gluon fusion process. Our Feynman rules are publicly available as a set of Universal FeynRules Object libraries called SM_Loop_VPolar.

Search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state in proton-proton collisions at [formula omitted

A search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state is presented. The analysis is based on proton-proton collision data recorded by the CMS detector in 2016–2018 at a centre-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 138fb−1. The search is sensitive to resonances with masses between 1.3 and 6TeV, decaying to bosons that are highly Lorentz-boosted such that each of the bosons forms a single large-radius jet. Machine learning techniques are employed to identify such jets. No significant excess over the estimated standard model background is observed. A maximum local significance of 3.6 standard deviations, corresponding to a global significance of 2.3 standard deviations, is observed at masses of 2.1 and 2.9 TeV. In a heavy vector triplet model, spin-1 Z′ and W′ resonances with masses below 4.8TeV are excluded at the 95% confidence level (CL). These limits are the most stringent to date. In a bulk graviton model, spin-2 gravitons and spin-0 radions with masses below 1.4 and 2.7TeV, respectively, are excluded at 95% CL. Production of heavy resonances through vector boson fusion is constrained with upper cross section limits at 95% CL as low as 0.1fb.

Combination of searches for heavy resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton–proton collisions at [formula omitted] and 13 TeV

A statistical combination of searches is presented for massive resonances decaying to WW, WZ, ZZ, WH, and ZH boson pairs in proton–proton collision data collected by the CMS experiment at the LHC. The data were taken at centre-of-mass energies of 8 and 13 TeV, corresponding to respective integrated luminosities of 19.7 and up to 2.7 fb−1. The results are interpreted in the context of heavy vector triplet and singlet models that mimic properties of composite-Higgs models predicting W′ and Z′ bosons decaying to WZ, WW, WH, and ZH bosons. A model with a bulk graviton that decays into WW and ZZ is also considered. This is the first combined search for WW, WZ, WH, and ZH resonances and yields lower limits on masses at 95% confidence level for W′ and Z′ singlets at 2.3 TeV, and for a triplet at 2.4 TeV. The limits on the production cross section of a narrow bulk graviton resonance with the curvature scale of the warped extra dimension k˜=0.5, in the mass range of 0.6 to 4.0 TeV, are the most stringent published to date.

Coupling WW, ZZ unitarized amplitudes to gamma gamma in the TeV region

We define and calculate helicity partial-wave amplitudes for processes linking the Electroweak Symmetry Breaking Sector (EWSBS) to gamma gamma , employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the Equivalence Theorem, while neglecting all particle masses. The resulting amplitudes can be useful in the energy regime (500~mathrm{{GeV}}{-}3~mathrm{{TeV}}). We also deal with their unitarization so that resonances of the EWSBS can simultaneously be described in the gamma gamma initial or final states. Our resulting amplitudes satisfy unitarity, perturbatively in alpha , but for all s values. In this way we improve on the HEFT that fails as interactions become stronger with growing s and we provide a natural framework for the decay of dynamically generated resonances into WW, ZZ and gamma gamma pairs.

TtH production at 13 TeV (CMS)

First results of a search for the Standard Model Higgs boson produced in association with a top quark-antiquark pair (ttH) in proton-proton collisions at a center of mass energy of 13 TeV is presented. The decays of Higgs boson into two photons, bottom quark-antiquark pair and multileptons via WW, ZZ and tautau pairs are analysed separately and then combined. The results are presented in terms of the best-fit signal strength relative to the Standard Model prediction and the observed and expected upper limits at the 95% confidence level are extracted.

Golden Probe of Electroweak Symmetry Breaking.

The ratio of the Higgs couplings to WW and ZZ pairs, λ_{WZ}, is a fundamental parameter in electroweak symmetry breaking as well as a measure of the (approximate) custodial symmetry possessed by the gauge boson mass matrix. We show that Higgs decays to four leptons are sensitive, via tree level or one-loop interference effects, to both the magnitude and, in particular, overall sign of λ_{WZ}. Determining this sign requires interference effects, as it is nearly impossible to measure with rate information. Furthermore, simply determining the sign effectively establishes the custodial representation of the Higgs boson. We find that h→4ℓ (4ℓ≡2e2μ, 4e, 4μ) decays have excellent prospects of directly establishing the overall sign at a high luminosity 13TeV LHC. We also examine the ultimate LHC sensitivity in h→4ℓ to the magnitude of λ_{WZ}. Our results are independent of other measurements of the Higgs boson couplings and, in particular, largely free of assumptions about the top quark Yukawa couplings which also enter at one loop. This makes h→4ℓ a unique and independent probe of electroweak symmetry breaking and custodial symmetry.

Search for heavy resonances in theℓℓqqfinal state inppcollisions at p √s = 13 TeV with ATLAS

A search for heavy resonances decaying to a pair of Z bosons is performed using proton–proton collision data produced at √s = 13 TeV and recorded by the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 3.2 fb−1 . Diboson resonant production is expected in several Standard Model extension scenarios. The ZZ decay mode considered corresponds to one Z boson decaying to a pair of charged leptons and the other decaying to a pair of quarks. No evidence for the production of resonances decaying to a ZZ pair is observed. Upper bounds on the production cross sections at √s = 13 TeV times their decay branching ratios to ZZ pairs are derived for a heavy Higgs boson and a spin–2 Randall-Sundrum graviton scenario.

Threshold resummation forW±ZandZZpair production at the LHC

We perform the threshold resummation for WZ and ZZ pair production at the next-to-next-to-leading logarithmic accuracy in Soft-Collinear Effective Theory at the LHC. Our results show that the resummation effects increase the total cross sections by about 7% for ZZ production and 12% for WZ production with$\sqrt{S}= 7,~8,~13 and 14 TeV, respectively, and the scale uncertainties are significantly reduced. Besides, our numerical results are well consistent with experimental data reported by the ATLAS and CMS collaborations.

Search for the Standard Model Higgs boson in the decay channel H → ZZ (*) → 4l at CMS

A search for the Standard Model (SM) Higgs boson in the decay channel H → ZZ( ∗ ) → 4l with each Z boson decaying to an electron or muon pair is presented using pp collisions from the LHC at \(\sqrt s = 7\) TeV. The data analysed correspond to an integrated luminosity of 1.66 ±0.07 fb − 1 recorded by the CMS detector in 2010 and 2011. The search covers Higgs boson mass (mH) hypotheses of \(110 < m_{\rm H} < 600~{\rm GeV/c^{2}}\). Twenty-one events are observed, while 21.2 ±0.8 events are expected from Standard Model (SM) background processes. The events are not clustered in mass excluding interpretation as the SM Higgs boson and its (4l) mass distribution is consistent with the expectation of SM continuum production of ZZ( ∗ ) pairs. Upper limits at 95% CL on the cross-section × branching ratio for a SM Higgs boson with SM like decays exclude cross-sections from about once to twice the expected SM cross-section for masses in the range of \(150< m_{\rm H} < 420~{\rm GeV/c^{2}}\).

Higgs production and decay with a fourth Standard-Model-like fermion generation

State-of-the-art predictions for the Higgs-boson production cross section via gluon fusion and for all relevant Higgs-boson decay channels are presented in the presence of a fourth Standard-Model-like fermion generation. The qualitative features of the most important differences to the genuine Standard Model are pointed out, and the use of the available tools for the predictions is described. For a generic mass scale of 400−600 GeV in the fourth generation explicit numerical results for the cross section and decay widths are presented, revealing extremely large electroweak radiative corrections, e.g., to the cross section and the Higgs decay into WW or ZZ pairs, where they amount to about −50 % or more. This signals the onset of a non-perturbative regime due to the large Yukawa couplings in the fourth generation. An estimate of the respective large theoretical uncertainties is presented as well.

Search for the Standard Model Higgs Boson in the Decay ChannelH→ZZ→4linppCollisions ats=7 TeV

A search for a Higgs boson in the four-lepton decay channel H to ZZ, with each Z boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range 110 < mH < 600 GeV. The analysis uses data corresponding to an integrated luminosity of 4.7 inverse femtobarns recorded by the CMS detector in pp collisions at sqrt(s) = 7 TeV from the LHC. Seventy-two events are observed with four-lepton invariant mass m[4 leptons] > 100 GeV (with thirteen below 160 GeV), while 67.1 +/- 6.0 (9.5 +/-1.3) events are expected from background. The four-lepton mass distribution is consistent with the expectation of standard model background production of ZZ pairs. Upper limits at 95% confidence level exclude the standard model Higgs boson in the ranges 134-158 GeV, 180-305 GeV, and 340 -465 GeV. Small excesses of events are observed around masses of 119, 126, and 320 GeV, making the observed limits weaker than expected in the absence of a signal.

Heavy Higgs boson at the Tevatron and the LHC in universal extra dimension models

Universal Extra Dimension (UED) models tend to favor a distinctively heavier Higgs mass than in the Standard Model (SM) and its supersymmetric extensions when the Kaluza-Klein (KK) scale is not much higher than the electroweak one, which we call the weak scale UED, in order to cancel the KK top contributions to the T-parameter. Such a heavy Higgs, whose production through the gluon fusion process is enhanced by the KK top loops, is fairly model independent prediction of the weak scale UED models regardless of the brane-localized mass structure at the ultraviolet cutoff scale. We study its cleanest possible signature, the Higgs decay into a Z boson pair and subsequently into four electrons and/or muons, in which all the four-momenta of the final states can be measured and both the Z boson masses can be checked. We show that the weak scale UED model may account for the 2sigma excess of this event at ATLAS at the ZZ pair invariant mass around 250GeV, at which scale SM background is sufficiently small and the SM Higgs predicts too few events. We have also studied the Higgs mass 500GeV (and also 700GeV with \sqrt{s}=14TeV) and have found that we can observe significant resonance with the integrated luminosity 10fb^{-1} for six dimensional UED models.

String theory at LHC using Higgs production and decay from string balls

We study Higgs production and decay from TeV scale string balls in pp collisions at $ \sqrt {s} = 14\;{\text{TeV}} $ at LHC. We present the results of total cross section of diphotons, invariant mass distribution of the diphotons and p T distribution of the diphotons and ZZ pairs from Higgs from string balls at LHC. We find that the invariant mass distribution of diphotons from Higgs from string balls is not very sensitive to the increase in diphoton invariant mass. We find that for string mass scale M s =2.5 TeV, which is the lower limit of the string mass scale set by the recent CMS collaboration at LHC, the $ \frac{{d\sigma }}{{d{p_T}}} $ of high p T (≥450 GeV) diphotons and ZZ pairs produced from Higgs from string balls is larger than that from standard model Higgs. Hence in the absence of black hole production at LHC an enhancement of high p T diphotons and ZZ pairs at LHC can be useful signatures for string theory at LHC. Since the matrix element for Higgs production in parton-parton collisions via string regge excitations is not available we compute $ \frac{{d\sigma }}{{d{p_T}}} $ of photon production from string regge excitations and make a comparison with that from string balls at LHC. We find that for string mass scale M s = 2.5 TeV the $ \frac{{d{\sigma_{photon}}}}{{d{p_T}}} $ from string regge excitations is larger than that from string balls and black holes at LHC.

Higher-order QCD effects in the Higgs to ZZ search channel at the LHC

We present a consistent analysis of the signal as well as the irreducible background for the search of the SM Higgs boson in the ZZ decay channel at the LHC. Soft-gluons effects are resummed up to next-to-leading logarithmic accuracy, and the results are compared to those obtained with fixed order calculations and the MC@NLO event generator. The soft-gluon effects are typically modest but should be taken into account when precise predictions are demanded. Our results show that the signal over background ratio can be significantly enhanced with a cut on the transverse momentum pTZZ of the ZZ pair. We also introduce a fully transverse angular variable that could give information about the CP nature of the Higgs boson.

Constitutive heterochromatin, 5S and 18S rDNA genes in Apareiodon sp. (Characiformes, Parodontidae) with a ZZ/ZW sex chromosome system

Karyotype, sex chromosome system and cytogenetics characteristics of an unidentified species of the genus Apareiodon originating from Piquiri River (Paraná State, Brazil) were investigated using differential staining techniques (C-banding and Ag-staining) and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes. The diploid chromosome number was 2n = 54 with 25 pairs of meta- (m) to submetacentric (sm) and 2 pairs of subtelocentric (st) chromosomes. The major ribosomal rDNA sites as revealed by Ag-staining and FISH with 18S rDNA probe were found in distal region of longer arm of st chromosome pair 26, while minor 5S sites were observed in the interstitial sites on chromosome pairs 2 (smaller cluster) and 7 (larger one). The C-positive heterochromatin had pericentromeric and telomeric distribution. The heteromorphic sex chromosome system consisted of male ZZ (pair 21) and female middle-sized m/st Z/W chromosomes. The pericentric inversion of heterochromatinized short arm of ancestral Z followed by multiplication of heterochromatin segments is hypothesized for origin of W chromosome. The observed karyotype and chromosomal markers corresponded to those found in other species of the genus.

Scent Marking Around the Breeding Season in Two Newly Formed Mexican Grey Wolf (Canis lupus baileyi) Pairs Kept in Captivity

The aim of the study was to analyse the scent marking patterns in frequency, type and position throughout the reproductive period of two pairs of Canis lupus baileyi housed in two zoos (LZ = Leon and ZZ = Zacango), in terms of newly and established pairs. Focal behaviour sampling was used to register 1,211 scent markings. Data were grouped in three periods: before, during, after and posterior to the reproductive season. Between newly formed pairs no significant difference was found in the previous period (U = 6.50, p>0.065); also, no significant difference was observed in the double marking (U = 54.0, p>0.083) during the reproductive season, although it was greater in the LZ compared to the ZZ pair. After commingling together for one year the established LZ couple, showed an increase in double marking (U = 16.5, p<0.001) during the mating period in comparison with the prior year. Male wolves marked with greater frequency with the leg raised in both, the double and single marking, whereas females marked more in a squatting position. It is concluded that scent marking is different in recently formed pairs in captivity, which are found in a reduced space and have not free choice to elect its mate

Equal frequencies of recombination nodules in both sexes of the pigeon suggest a basic difference with eutherian mammals

The total number of recombination nodules (RNs) in the autosomal synaptonemal complexes (SCs) is statistically equivalent in oocytes and spermatocytes from the domestic pigeon Columba livia. The distribution on RNs along the three longest autosomes is also equivalent in oocytes and spermatocytes. The numbers of RNs show a linear relationship when plotted against SC length both in oocytes and spermatocytes. On the other hand, the ZW pair shows a single and strictly localized RN near the synaptic termini, but the ZZ pair shows unrestricted location of RNs (average 3.8). The ZW and ZZ pairs of the pigeon are euchromatic and do not show specific chromatin packing at pachytene in either sex. The lack of sex-specific differences in the number and location of RNs in the autosomal bivalents of C. livia and previous data on the chicken, suggest that the regulation of crossing-over is basically different in birds and mammals.

Quantum Monte Carlo study of spin [formula omitted] chains

Disorder of anisotropy is introduced into spin 1 2 quantum XXZ chains. This model, which is refered as the spin 1 2 ± J z chain, is studied by the quantum Monte Carlo method. It displays the critical phenomena of the x− y phase, though the critical exponents γ, η and ν must be corrected. However, the antiferromagnetic alternating spin chains show no critical phenomena. It is found that the susceptibility along the z axis and averaged zz pair spin correlation functions of alternating spin chains show obviously different behavior from those of ± J z chains.

Four weak gauge boson production at photon linear collider and heavy Higgs signal

We study the signals and backgrounds for a heavy Higgs boson in the processes γγ → WWWW, γ → WWZZ at the proton linear collider. The results are based on the complete tree-level SM calculation for these reactions. We show that the invariant mass spectrum of central WW, ZZ pairs is sensitive to the signal from Higgs boson with a mass up to 1 TeV linear collider for integrated luminosity of 300 fb −1. At 1.5 TeV PLC Higgs boson with a mass up to 700 GeV can be studied. The nonresonant longitudinal gauge boson scattering ( m H = ∞) can be detected in photon-photon collisions at e + e − center-of-mass energy of 3 TeV.

Production of four-weak-bosons and heavy Higgs signals in TeV photon-photon collisions

We have studied the signals for a heavy Higgs boson in the processes γγ → WWWW, and γγ → WWZZ at a photon linear collider. The results are based on the first complete tree-level calculation for these reactions. We show that, with a forward “spectator” W tag, and a central “spectator” W veto to suppress backgrounds from transverse W, Z production, the invariant mass spectrum of central WW, ZZ pairs is sensitive to Higgs bosons with a mass up to 1 TeV in a 2-TeV linear collider.