Measurement of W-+/--boson and Z-boson production cross-sections in pp collisions at root s=2.76 TeV with the ATLAS detector
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb final state in pp collisions at s = 13 TeV with the ATLAS detector
A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb -1 from proton–proton collisions at $ \sqrt{s}=13 $ TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the Z boson decaying to electrons or muons and the H boson into a pair of b-quarks. No evidence for the production of an A boson is found. Considering each production process separately, the 95% confidence-level upper limits on the pp→A→ZH production cross-section times the branching ratio H→bb are in the range of 14–830 fb for the gluon–gluon fusion process and 26–570 fb for the b-associated process for the mass ranges 130–700 GeV of the H boson and 230–800 GeV of the A boson. The results are interpreted in the context of two-Higgs-doublet models.
Aaboud, M.↗
Measurement of W ± -boson and Z -boson production cross-sections in p p collisions at s = 2.76 TeV with the ATLAS detector
CERN-LHC. The production cross-sections for W± and Z bosons are measured using ATLAS data corresponding to an integrated luminosity of 4.0 pb−1 collected at a centre-of-mass energy sqrt(s) = 2.76 TeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for decays of the 125 GeV Higgs boson into a Z boson and a $\rho$ or $\phi$ meson
Decays of the 125 GeV Higgs boson into a Z boson and a ρ$^{0}$(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $ \sqrt{s} $ = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb$^{−1}$. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.[graphic not available: see fulltext]
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Higgs boson decays into Z and J/ψ and for Higgs and Z boson decays into J/ψ or Y pairs in pp collisions at s = 13 TeV
Decays of the Higgs boson into a z boson and a J/ψ or ψ(2S) meson are searched for in four-lepton final states with the CMS detector at the LHC. A data set of proton-proton collisions corresponding to an integrated luminosity of 138 fb -1 is used. Using the same data set, decays of the Higgs and z boson into quarkonium pairs are also searched for. An observation of such decays with this sample would indicate the presence of physics beyond the standard model. No evidence for these decays has been observed and upper limits at the 95% confidence level are placed on the corresponding branching fractions ($\mathscr{B}$). Assuming longitudinal polarization of the Higgs boson decay products, 95% confidence level observed upper limits for $\mathcal{B}$(H→ZJ/ψ) and $\mathcal{B}$(H→Zψ(2S)) are 1.9 X 10 -3 and 6.6 X 10 -3 , respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for the decay of the Higgs boson to a $Z$ boson and a light pseudoscalar particle decaying to two photons
A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at $\sqrt{s}$ = 13 TeV, corresponding to 139 fb –1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the $a$ particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the $a$ decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to $Za$ times the branching ratio $a → γγ$ are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the $a$ particle. The results are also interpreted in the context of ALP models.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a heavy pseudoscalar Higgs boson decaying to a 125 GeV Higgs boson and a Z boson in final states with two tau and two light leptons in proton-proton collisions at $\sqrt{s} = 13$ TeV
A search for a heavy pseudoscalar Higgs boson, A, decaying to a 125 GeV Higgs boson h and a Z boson is presented. The h boson is identified via its decay to a pair of tau leptons, while the Z boson is identified via its decay to a pair of electrons or muons. The search targets the production of the A boson via the gluon-gluon fusion process, gg → A, and in association with bottom quarks, $b\overline{b}A$. The analysis uses a data sample corresponding to an integrated luminosity of 138 fb −1 collected with the CMS detector at the CERN LHC in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV. Constraints are set on the product of the cross sections of the A production mechanisms and the A → Zh decay branching fraction. The observed (expected) upper limit at 95% confidence level ranges from 0.049 (0.060) pb to 1.02 (0.79) pb for the gg → A process and from 0.053 (0.059) pb to 0.79 (0.61) pb for the $b\overline{b}A$ process in the probed range of the A boson mass, mA, from 225 GeV to 1 TeV. The results of the search are used to constrain parameters within the $M^{125}_{h,EFT}$ benchmark scenario of the minimal supersymmetric extension of the standard model. Values of tan β below 2.2 are excluded in this scenario at 95% confidence level for all mA values in the range from 225 to 350 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a heavy pseudoscalar Higgs boson decaying into a 125 GeV Higgs boson and a Z boson in final states with two tau and two light leptons at $\sqrt{s}=$ 13 TeV
A search is performed for a pseudoscalar Higgs boson, A, decaying into a 125 GeV Higgs boson h and a Z boson. The h boson is specifically targeted in its decay into a pair of tau leptons, while the Z boson decays into a pair of electrons or muons. A data sample of proton-proton collisions collected by the CMS experiment at the LHC at $ \sqrt{s} $ = 13 TeV is used, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. No excess above the standard model background expectations is observed in data. A model-independent upper limit is set on the product of the gluon fusion production cross section for the A boson and the branching fraction to Zh → ℓℓττ. The observed upper limit at 95% confidence level ranges from 27 to 5 fb for A boson masses from 220 to 400 GeV, respectively. The results are used to constrain the extended Higgs sector parameters for two benchmark scenarios of the minimal supersymmetric standard model.[graphic not available: see fulltext]
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Non-Minimal Higgs Bosons from Z Boson Decay
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Komamiya, S.↗
Search for a heavy resonance decaying into a Z boson and a Z or W boson in 2ℓ2q final states at $ \sqrt{s}=13 $ TeV
In this paper, a search has been performed for new, heavy resonances decaying to ZZ or ZW in 2$\ell$2q final states, with two charged leptons ($\ell=$ e,$\mu$) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of $\sqrt{s}=$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W$'$ bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Higgs boson decays into a Z boson and a light hadronically decaying resonance in pp collisions at s =13 TeV with the ATLAS detector
A search for decays of the Higgs boson into a Z boson and a light resonance, with a mass of 0.5–3.5 GeV, is performed using the full 140 fb−1 dataset of 13 TeV proton–proton collisions recorded by the ATLAS detector during LHC Run 2. Leptonic decays of the Z boson and hadronic decays of the light resonance are considered. The resonance can be interpreted as a J / ψ or η c meson, an axion-like particle, or a light pseudoscalar predicted in two-Higgs-doublet models. Due to its low mass, this resonance is produced with a high Lorentz boost in the laboratory frame and therefore reconstructed as a single small-radius jet of hadrons. A neural network is used to correct the Monte Carlo simulation of the total expected background using data from sideband regions. Two additional neural networks are used to distinguish signal from background, enhancing the purity of the signal region. A binned profile-likelihood fit is performed on the final-state invariant mass distribution. No significant excess of events relative to the expected background is observed, and upper limits at 95% confidence level are set on the Higgs boson's branching fraction to a Z boson and a light resonance. The exclusion limit is ∼10% for the lower masses, and increases for higher masses. Upper limits on the effective coupling C Z H eff / Λ of an axion-like particle to a Higgs boson and Z boson are also set at 95% confidence level, and range from 0.9 to 2 TeV−1.
Aad, G↗
Search for an exotic decay of the Higgs boson into a Z boson and a pseudoscalar particle in proton-proton collisions at s = 13 TeV
A search for an exotic decay of the Higgs boson to a Z boson and a light pseudoscalar particle (a), decaying to a pair of leptons and a pair of photons, respectively, is presented. The search is based on proton-proton collision data at a center-of-mass energy of s = 13 TeV , collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 138 fb − 1 . The analysis probes pseudoscalar masses m a between 1 and 30 GeV, leading to two pairs of well-isolated leptons and photons. Upper limits at 95% confidence level are set on the Higgs boson production cross section times its branching fraction to two leptons and two photons. The observed (expected) limits are in the range of 1.1–17.8 (1.7–17.9)fb within the probed m a interval. An excess of data above the expected standard model background with a local (global) significance of 2.6 (1.3) standard deviations is observed for a mass hypothesis of m a = 3 GeV . Limits on models involving axion-like particles, formulated as an effective field theory, are also reported.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the ${\ell}^{+}{\ell}^{-}t\overline{t}$ and $\nu\overline{\nu}b\overline{b}$ final states using 140 fb –1 of data collected with the ATLAS detector
A search for a heavy CP-odd Higgs boson, A, decaying into a Z boson and a heavy CP-even Higgs boson, H, is presented. It uses the full LHC Run 2 dataset of pp collisions at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb –1 . The search for A → ZH is performed in the $ℓ^+ℓ^–t\bar{t}$ and $ν\bar{ν}b\bar{b}$ final states and surpasses the reach of previous searches in different final states in the region with mH > 350 GeV and mA > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed $m(t\bar{t}$) and $m(b\bar{b}$) distributions in the $ℓ^+ℓ^–t\bar{t}$ and $ν\bar{ν}b\bar{b}$ channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Higgs Boson Decays into a Z Boson and a Light Hadronically Decaying Resonance Using 13 TeV pp Collision Data from the ATLAS Detector
A search for Higgs boson decays into a Z boson and a light resonance in two-lepton plus jet events is performed, using a p p collision dataset with an integrated luminosity of 139 fb–1 collected at √ s = 13 TeV by the ATLAS experiment at the CERN LHC. The resonance considered is a light boson with a mass below 4 GeV from a possible extended scalar sector or a charmonium state. Multivariate discriminants are used for the event selection and for evaluating the mass of the light resonance. No excess of events above the expected background is found. Observed (expected) 95% confidence-level upper limits are set on the Higgs boson production cross section times branching fraction to a Z boson and the signal resonance, with values in the range 17–340 pb ($16^{+6}_{– 5}–320^{+130}_{–90}$ pb) for the different light spin-0 boson mass and branching fraction hypotheses, and with values of 110 and 100 pb ($100^{+40}_{–30}$ and $100^{+40}_{–30}$ pb ) for the $η_c$ and J/ψ hypotheses, respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the $\ell \ell bb$ and $\ell \ell WW$ final states in pp collisions at $\sqrt{s}=13$ $\text {TeV}$ with the ATLAS detector
A search for a heavy neutral Higgs boson, A decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 139 fb-1 from proton–proton collisions at $\sqrt{s} = 13$ TeV recorded by the ATLAS detector at the LHC. The search considers the Z boson decaying into electrons or muons and the H boson into a pair of b-quarks or W bosons. The mass range considered is 230–800 $\text {GeV}$ for the A boson and 130–700 $\text {GeV}$ for the H boson. The data are in good agreement with the background predicted by the Standard Model, and therefore 95% confidence-level upper limits for $\sigma \times B(A\rightarrow ZH)\times B(H\rightarrow bb \; \text {or} \; H \rightarrow WW)$ are set. The upper limits are in the range 0.0062–0.380 pb for the $H\rightarrow bb$ channel and in the range 0.023–8.9 pb for the $H\rightarrow WW$ channel. An interpretation of the results in the context of two-Higgs-doublet models is also given.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Z -boson decays to a vector quarkonium plus a photon
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Evidence for the Higgs Boson Decay to a $Z$ Boson and a Photon at the LHC
The first evidence for the Higgs boson decay to a Z boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision datasets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb –1 for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is 2.2 ± 0.7 times the standard model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing Z t t ¯ couplings using Z boson polarization in Z Z production at hadron colliders
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗