Scalar Resonances Research Articles

95 GeV excess in the Georgi-Machacek model: Single or twin peak resonance

In this work, we investigate the possibility to address the excess observed around 95 GeV in the γγ, ττ, and bb¯ channels as a scalar resonance(s) within the Georgi-Machacek model. In our analysis, we find that the excess can be easily accommodated in the channels (γγ and bb¯) simultaneously, where the 95 GeV candidate is a single peak resonance (SPR) due to a light CP-even scalar. We found that the excess in the ττ channel can be addressed simultaneously with γγ and bb¯ only if the 95 GeV candidate is a twin peak resonance (TPR), i.e., another CP-odd scalar in addition to the CP-even scalar. We demonstrate that the nature of the 95 GeV scalar resonance candidate (SPR or TPR) can be probed via the properties of its di-τ decay. Published by the American Physical Society 2024

Charmonium χc0 and χc2 resonances in coupled-channel scattering from lattice QCD

In order to explore the spectrum of hidden-charm scalar and tensor resonances, we study meson-meson scattering with JPC=0++,2++ in the charmonium energy region using lattice QCD. Employing a light-quark mass corresponding to mπ≈391 MeV, we determine coupled-channel scattering amplitudes up to around 4100 MeV considering all kinematically relevant channels consisting of a pair of open-charm mesons or a charmonium meson with a light meson. A single isolated scalar resonance near 4000 MeV is found with large couplings to DD¯, DsD¯s and the kinematically closed D*D¯* channel. A single tensor resonance at a similar mass couples strongly to DD¯, DD¯* and D*D¯*. We compare the extracted resonances to contemporary experimental candidate states, previous lattice results and theoretical modeling. In contrast to several other studies, we do not find any significant feature in the scalar amplitudes between the ground state χc0(1P) and the resonance found around 4000 MeV. Published by the American Physical Society 2024

Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD

We determine JPC=0++ and 2++ hadron-hadron scattering amplitudes in the charmonium energy region up to 4100 MeV using lattice QCD, a first-principles approach to QCD. Working at mπ≈391 MeV, more than 200 finite-volume energy levels are computed and these are used in extensions of the Lüscher formalism to determine infinite-volume coupled-channel scattering amplitudes. We find that this energy region contains a single χc0 and a single χc2 resonance. Both are found as pole singularities on the closest unphysical Riemann sheet, just below 4000 MeV with widths around 70 MeV. The largest couplings are to kinematically closed D*D¯* channels in S-wave, and couplings to several decay channels consisting of pairs of open-charm mesons are found to be large and significant in both cases. Above the ground state χc0, no other scalar bound states or near-DD¯ threshold resonances are found, in contrast to several theoretical and experimental studies. Published by the American Physical Society 2024

Combination of Searches for Resonant Higgs Boson Pair Production Using pp Collisions at sqrt[s]=13 TeV with the ATLAS Detector.

A combination of searches for a new resonance decaying into a Higgs boson pair is presented, using up to 139 fb^{-1} of pp collision data at sqrt[s]=13 TeV recorded with the ATLAS detector at the LHC. The combination includes searches performed in three decay channels: bb[over ¯]bb[over ¯], bb[over ¯]τ^{+}τ^{-}, and bb[over ¯]γγ. No excess above the expected Standard Model background is observed and upper limits are set at the 95% confidence level on the production cross section of Higgs boson pairs originating from the decay of a narrow scalar resonance with mass in the range 251GeV-5TeV. The observed (expected) limits are in the range 0.96-600fb (1.2-390fb). The limits are interpreted in the type-I two-Higgs-doublet model and the minimal supersymmetric standard model, and constrain parameter space not previously excluded by other searches.

Study of a near-threshold scalar resonance in the $$\omega \phi $$ system in pion-Be interaction at momentum of 29 GeV

Study of a near-threshold scalar resonance in the $$\omega \phi $$ system in pion-Be interaction at momentum of 29 GeV

Dynamical generation of the scalar f0(500) , f0(980) , and K0*(700) resonances in the Ds+→K+π+π− reaction

We develop a model aimed at understanding the three mass distributions of pairs of mesons in the Cabibbo-suppressed Ds+→K+π+π− decay recently measured with high statistics by the BESIII collaboration. The largest contributions to the process come from the Ds+→K+ρ0 and Ds+→K*0π+ decay modes, but the Ds+→K0*(1430)π+ and Ds+→K+f0(1370) modes also play a moderate role and all of them are introduced empirically. Instead, the contribution of the f0(500), f0(980), and K0*(700) resonances is introduced dynamically by looking at the decay modes at the quark level, hadronizing qq¯ pairs to give two mesons, and allowing these mesons to interact, for which we follow the chiral unitary approach, to finally produce the K+π+π− final state. While the general features of the mass distributions are fairly obtained, we pay special attention to the specific effects created by the light scalar resonances, which are visible in the low mass region of the π+π−(f0(500)) and K+π−(K0*(700)) mass distributions and a narrow peak for π+π− distribution corresponding to f0(980) excitation. The contribution of these three resonances is generated by only one parameter. We see the agreement found in these regions as further support for the nature of the light scalar states as dynamically generated from the interaction of pseudoscalar mesons. Published by the American Physical Society 2024

S -wave contribution to rare D0→π+π−ℓ+ℓ− decays in the standard model and sensitivity to new physics

Physics of the up-type flavor offers unique possibilities of testing the standard model (SM) compared to the down-type flavor sector. Here, we discuss SM and new physics (NP) contributions to the rare charm-meson decay D0→π+π−ℓ+ℓ−. In particular, we discuss the effect of including the lightest scalar isoscalar resonance in the SM picture, namely, the f0(500), which manifests in a big portion of the allowed phase space. Other than showing in the total branching ratio at an observable level of about 20%, the f0(500) resonance manifests as interference terms with the vector resonances, such as at high invariant mass of the leptonic pair in distinct angular observables. Recent data from LHCb optimize the sensitivity to P-wave contributions that we analyze in view of the inclusion of vector resonances. We propose the measurement of alternative observables that are sensitive to the S-wave and are straightforward to implement experimentally. This leads to a new set of null observables that vanish in the SM due to its gauge and flavor structures. Finally, we study observables that depend on the SM interference with generic NP contributions from semileptonic four-fermion operators in the presence of the S-wave. Published by the American Physical Society 2024

First shot of the smoking gun: probing the electroweak phase transition in the 2HDM with novel searches for A → ZH in ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} and ννbb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \ u b\\overline{b} $$\\end{document} final states

Recently the ATLAS collaboration has reported the first results of searches for heavy scalar resonances decaying into a Z boson and a lighter new scalar resonance, where the Z boson decays leptonically and the lighter scalar decays into a top-quark pair, giving rise to ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} final states. This had previously been identified as a smoking-gun signature at the LHC for a first-order electroweak phase transition (FOEWPT) within the framework of two Higgs doublet models (2HDMs). In addition, ATLAS also presented new limits where the Z boson decays into pairs of neutrinos and the lighter scalar resonance into bottom-quark pairs, giving rise to the ννbb¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \ u b\\overline{b} $$\\end{document} final state. We analyze the impact of these new searches on the 2HDM parameter space, with emphasis on their capability to probe currently allowed 2HDM regions featuring a strong FOEWPT. We also study the complementarity of these new searches with other LHC probes that could target the FOEWPT region of the 2HDM. Remarkably, the ATLAS search in the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} final state shows a local 2.85 σ excess (for masses of about 650 GeV and 450 GeV for the heavy and light resonance) in the 2HDM parameter region that would yield a FOEWPT in the early universe, which could constitute the first experimental hint of baryogenesis at the electroweak scale. We analyze the implications of this excess, and discuss the detectability prospects for the associated gravitational wave signal from the FOEWPT. Furthermore, we project the sensitivity reach of the ℓ+ℓ−tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\ell}^{+}{\\ell}^{-}t\\overline{t} $$\\end{document} signature for the upcoming runs of the LHC. Finally, we introduce the python package thdmTools, a state-of-art tool for the exploration of the 2HDM.

Accommodating a 650 GeV scalar resonance in HEFT

Accommodating a 650 GeV scalar resonance in HEFT

A new LHC search for dark matter produced via heavy Higgs bosons using simplified models

Searches for dark matter produced via scalar resonances in final states consisting of Standard Model (SM) particles and missing transverse momentum are of high relevance at the LHC. Motivated by dark-matter portal models, most existing searches are optimized for unbalanced decay topologies for which the missing momentum recoils against the visible SM particles. In this work, we show that existing searches are also sensitive to a wider class of models, which we characterize by a recently presented simplified model framework. We point out that searches for models with a balanced decay topology can be further improved with more dedicated analysis strategies. For this study, we investigate the feasibility of a new search for bottom-quark associated neutral Higgs production with a boverline{b}Z+{p}_{textrm{T}}^{textrm{miss}} final state and perform a detailed collider analysis. Our projected results in the different simplified model topologies investigated here can be easily reinterpreted in a wide range of models of physics beyond the SM, which we explicitly demonstrate for the example of the Two-Higgs-Doublet model with an additional pseudoscalar Higgs boson.

Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t → qX (q = u, c), with X → boverline{b} , in proton-proton collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X → boverline{b} , and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction mathcal{B} (t → uX) and between 0.018% and 0.078% for the branching fraction mathcal{B} (t → cX), for masses of the scalar particle X between 20 and 160 GeV.

Search for Higgs boson pair production in association with a vector boson in pp collisions at sqrt{s}=13,text {TeV} with the ATLAS detector

This paper reports a search for Higgs boson pair (hh) production in association with a vector boson (W; {text {o}r}; Z) using 139 fb^{-1} of proton–proton collision data at sqrt{s}=13,text {TeV} recorded with the ATLAS detector at the Large Hadron Collider. The search is performed in final states in which the vector boson decays leptonically (Wrightarrow ell nu ,, Zrightarrow ell ell ,nu nu with ell =e, mu ) and the Higgs bosons each decay into a pair of b-quarks. It targets Vhh signals from both non-resonant hh production, present in the Standard Model (SM), and resonant hh production, as predicted in some SM extensions. A 95% confidence-level upper limit of 183 (87) times the SM cross-section is observed (expected) for non-resonant Vhh production when assuming the kinematics are as expected in the SM. Constraints are also placed on Higgs boson coupling modifiers. For the resonant search, upper limits on the production cross-sections are derived for two specific models: one is the production of a vector boson along with a neutral heavy scalar resonance H, in the mass range 260–1000 GeV, that decays into hh, and the other is the production of a heavier neutral pseudoscalar resonance A that decays into a Z boson and H boson, where the A boson mass is 360–800 GeV and the H boson mass is 260–400 GeV. Constraints are also derived in the parameter space of two-Higgs-doublet models.

Introducing tools to test Higgs boson interactions via WW scattering. II. The coupled-channel formalism and scalar resonances

In this work we explore in detail the presence of scalar resonances in $WW$ fusion process in the context of the LHC experiments working in the theoretical framework provided by Higgs Effective Field Theories (HEFT). While the phenomenology of vector resonances is reasonably understood in the framework of Weinberg sum-rules and unitarization studies, scalar resonances are a lot less constrained and, more importantly do depend on HEFT low-energy effective couplings different from the ones of vector resoances that are difficult to constrain experimentally. More specifically, unitarization techniques combined with the requirement of causality allows us to set non-trivial bounds on Higgs self-interactions. This is due to the need of considering coupled channels in the scalar case along the unitarization process. As a byproduct, we can gain some relevant information on the Higgs sector from $WW\to WW$ elastic processes without needing to consider two Higgs production.

J/ψ decay to ϕ,ω,K⁎0 plus f0(1370), f0(1710), [formula omitted], f2(1270), [formula omitted] and [formula omitted]: Role of the D-wave for tensor production

We reassess the decay of the J/ψ into an ω,ϕ,K⁎0 and one of the f0(1370), f0(1710), f2(1270), f2′(1525), K0⁎(1430) and K2⁎(1430) resonances. We benefit from previous works that considered this reaction as a J/ψ decay into three vector mesons, with a scalar or tensor resonance being formed from the interaction of two of these vectors. The novelty here with respect to former studies is the investigation of the relation between the scalar meson and tensor productions for the first time. To this end, the spin structure of the four vectors present in the production vertex is analyzed, and the D-wave mechanism in the tensor production is included. Then, beyond the ratios studied previously involving scalar states and tensor states independently, new ratios relating the scalar and tensor meson productions are estimated. Our results suggest that the D-wave mechanism of tensor production assumes a relevant contribution. New experimental data reporting the angular distributions of these processes will be important for checking this conclusion.

The scalar exotic resonances X(3915), X(3960), X_0(4140)

The scalar resonances X(3915), X(3960), X_0(4140) are considered as exotic four-quark states: cqbar{c} bar{q}, csbar{c} bar{s}, csbar{c}bar{s}, while the X(3863) is proved to be the cbar{c}, 2,^3P_0 state. The masses and the widths of these resonances are calculated in the framework of the Extended Recoupling Model, where a four-quark system is formed inside the bag and has relatively small size (lesssim 1.0 fm). Then the resonance X(3915) appears due to the transitions: J/psi omega into D^{*+}D^{*-} (or D^{*0}bar{D}^{*0}) and back, while the X(3960) is created due to the transitions D_s^+D_s^- into J/psi phi and back, and the X_0(4140) is formed in the transitions J/psi phi into D_s^{*+}D_s^{*-} and back. The characteristic feature of the recoupling mechanism is that this type of resonances can be predominantly in the S-wave decay channels and has J^P=0^+. In two-channel case the resonance occurs to be just near the lower threshold, while due to coupling to third channel (like the cbar{c} channel) it is shifted up and lies by (20–30) MeV above the lower threshold. The following masses and widths are calculated: M(X(3915))=3920 MeV, Gamma (X(3915))=20 MeV; M(X(3960))=3970 MeV, Gamma (X(3960)=45(5) MeV, M(X_0(4140))= 4120(20) MeV, Gamma (X_0(4140))=100 MeV, which are in good agreement with experiment.

Modeling the resonance Tcs0a(2900)++ as a hadronic molecule D*+K*+

The doubly charged scalar resonance $T_{cs0}^{a}(2900)^{++}$ is studied in the context of the hadronic molecule model. We consider $ T_{cs0}^{a}(2900)^{++}$ as a molecule $M=D^{\ast +}K^{\ast +}$ composed of vector mesons, and calculate its mass, current coupling and full width. The spectroscopic parameters of $M$, i.e., its mass and current coupling, are found by means of the QCD two-point sum rule method by taking into account vacuum expectation values of quark, gluon and mixed operators up to dimension $10$. The width of the molecule $M$ is evaluated through the calculations of the partial widths of the decay channels $M \to D_{s}^{+}\pi^{+}$, $M \to D_{s}^{\ast +}\rho^{+}$, and $M \to D^{\ast +}K^{\ast +}$. Partial widths of these processes are determined by strong couplings $g_1$, $g_2$, and $g_3$ of particles at vertices $ MD_{s}^{+}\pi^{+} $, $MD_{s}^{\ast +}\rho^{+}$, and $M D^{\ast +}K^{\ast +}$ , respectively. We calculate the couplings $g_i$ by employing the QCD light-cone sum rule approach and technical tools of the soft-meson approximation. Predictions obtained for the mass $m=(2924 \pm 107)~\mathrm{ MeV}$ and width $\Gamma=(123 \pm 25)~\mathrm{MeV}$ of the hadronic molecule $ M$ allow us to consider it as a possible candidate of the resonance $ T_{cs0}^{a}(2900)^{++}$.

On the structures of new scalar resonances and

We investigate properties of the new scalar resonances and , which were recently reported by the LHCb collaboration. These states were observed as resonant structures in and invariant mass distributions in B + meson decays. We argue that and may be modeled as molecules and of conventional vector mesons, respectively. The mass m and current coupling f of the molecule are calculated using a two-point sum rule method. The sum rule analysis is performed by taking into account vacuum condensates up to dimension 8. The obtained result for the mass, m = (2917 ± 135) MeV, permits us to consider the molecule as one of the possible models of the resonance . Because the second structure is isospin partner of the doubly charged state, it should have a mass close to m.

Prospects for Higgs boson and new scalar resonant production searches in ttbb final state at the LHC

In this article we probe resonant associated production of a Standard Model Higgs boson with new heavy scalar resonance in proton-proton collisions at a center-of-mass energy s=13 TeV. The Higgs boson and new scalar resonant are required to decay into a pair of bottom quarks and a pair of top quarks, respectively. Semileptonic decay of top quarks is considered. The searches are projected into operation conditions of the Large Hadron Collider during Run II data taking period at a center-of-mass energy of 13 TeV using Monte Carlo generated events, realistic detector response simulation and available Open Data samples. Analysis strategies are presented and machine learning approach using Deep Neural Network is proposed to resolve ambiguous in jets assignment and improve kinematic reconstruction of signal events. Sensitivity of the CMS detector is estimated as 95% expected upper limits on the product of the production cross section and the branching fractions of the searched particles.

Prospects for γ⋆γ⋆→ππ via lattice QCD

The $\gamma^\star \gamma^\star \to \pi \pi$ scattering amplitude plays a key role in a wide range of phenomena, including understanding the inner structure of scalar resonances as well as constraining the hadronic contributions to the anomalous magnetic moment of the muon. In this work, we explain how the infinite-volume Minkowski amplitude can be constrained from finite-volume Euclidean correlation functions. The relationship between the finite-volume Euclidean correlation functions and the desired amplitude holds up to energies where $3\pi$ states can go on shell, and is exact up to exponentially small corrections that scale like $\mathcal{O}(e^{-m_\pi L})$, where $L$ is the spatial extent of the cubic volume and $m_\pi$ is the pion mass. In order to implement this formalism and remove all power-law finite volume errors, it is necessary to first obtain $\pi \pi \to \pi\pi$, $\pi \gamma^\star \to \pi$, $\gamma^\star \to\pi\pi$, and $\pi\pi\gamma^\star \to\pi\pi$ amplitudes; all of which can be determined via lattice quantum chromodynamic calculations.

Evolution of scalar field resonances in a braneworld

In this work, we investigate the numerical evolution of massive Kaluza–Klein (KK) modes of a scalar field in a thick brane. We derive the Klein–Gordon equation in five-dimensional spacetime, and obtain the evolution equation and the Schrödinger-like equation. With the resonances of the scalar KK modes as the initial data, the scalar field is evolved with the maximally dissipative boundary condition. The results show that there are scalar KK resonant particles with long life on the brane, which indicates that these resonances might be regarded as a candidate for dark matter.