Decay Widths Research Articles

Observation of an Excess of Dicharmonium Events in the Four-Muon Final State with the ATLAS Detector.

A search is made for potential ccc[over ¯]c[over ¯] tetraquarks decaying into a pair of charmonium states in the four muon final state using proton-proton collision data at sqrt[s]=13 TeV, corresponding to an integrated luminosity of 140 fb^{-1} recorded by the ATLAS experiment at LHC. Two decay channels, J/ψ+J/ψ→4μ and J/ψ+ψ(2S)→4μ, are studied. Backgrounds are estimated based on a hybrid approach involving MonteCarlo simulations and data-driven methods. Statistically significant excesses with respect to backgrounds dominated by the single parton scattering are seen in the di-J/ψ channel consistent with a narrow resonance at 6.9GeV and a broader structure at lower mass. A statistically significant excess is also seen in the J/ψ+ψ(2S) channel. The fitted masses and decay widths of the structures are reported.

On the importance of three-body decays of vector-like quarks

It is a common feature of vector-like extensions of the electroweak sector to have near degenerate states, such as electroweak doublets. In simplified models, it is usually assumed that these have decay widths saturated by two-body channels. As a consequence, experimental searches can be done focusing on only one of the states of the doublet. Taking as an example case the light exotic electroweak doublet present in the Minimal Composite Higgs Model, we show that including three-body decays in the pair production process makes this separation unfeasible, since both states of the doublet will be present and contribute significantly to the signal. In addition, by recasting present searches in multileptonic channels, with a simplified cut-and-count analysis, a relevant increase in discovery reach or exclusion potential is obtained; this indeed motivates a more detailed analysis. This study shows how an inclusive search strategy, taking into account both the near degeneracy and the presence of three-body decays, will have greater discovery power and be more natural from a model building perspective.

Resonance-aware NLOPS matching for off-shell toverline{t} + tW production with semileptonic decays

The increasingly high accuracy of top-quark studies at the LHC calls for a theoretical description of toverline{t} production and decay in terms of exact matrix elements for the full 2 → 6 process that includes the off-shell production and the chain decays of toverline{t} and tW intermediate states, together with their quantum interference. Corresponding NLO QCD calculations matched to parton showers are available for the case of dileptonic channels and are implemented in the bb4l Monte Carlo generator, which is based on the resonance-aware POWHEG method. In this paper, we present the first NLOPS predictions of this kind for the case of semileptonic channels. In this context, the interplay of off-shell toverline{t} + tW production with various other QCD and electroweak subprocesses that yield the same semileptonic final state is discussed in detail. On the technical side, we improve the resonance-aware POWHEG procedure by means of new resonance histories based on matrix elements, which enable a realistic separation of toverline{t} and tW contributions. Moreover, we introduce a general approach which makes it possible to avoid certain spurious terms that arise from the perturbative expansion of decay widths in any off-shell higher-order calculation, and which are large enough to jeopardise physical finite-width effects. These methods are implemented in a new version of the bb4l Monte Carlo generator, which is applicable to all dileptonic and semileptonic channels, and can be extended to fully hadronic channels. The presented results include a NLOPS comparison of off-shell against on-shell toverline{t} + tW production and decay, where we highlight various non-trivial aspects related to NLO and parton-shower radiation in leptonic and hadronic top decays.

Rethinking the Pc(4457)+ as the [formula omitted] isoquartet [formula omitted] molecule

The nature of the Pc(4312), Pc(4440) and Pc(4457) pentaquarks is a fascinating theoretical question. Within the molecular picture their more usual interpretation is that of I=12D¯Σc and D¯⁎Σc bound states. Here we argue in favor of interpreting the Pc(4457) pentaquark as a I=32D¯⁎Σc bound state (with spin J=12) instead. Owing to isospin symmetry breaking effects, with this identification the partial decay width of the Pc(4457)+ into J/ψp will be of the same order of magnitude as the Pc(4312)+ and Pc(4440)+, in contrast with the considerably larger partial decay width in the I=12 scenario. In turn, this leads to a different hidden-charm molecular pentaquark spectrum, in which there are only four or five PψN bound states instead of the usual seven, which might explain why the predicted J=12 and 32 (I=12) D¯⁎Σc⁎ molecular partners of the Pc(4312) and Pc(4440) have not been observed.

DM-SM interactions mediated by spin-one particles: EFT study

Standard model-dark matter particles, mediated by spin one fields, are analyzed within the effective field theory framework. We [1, 2] consider dark particles masses from few MeV to 6.4 TeV. We restrict the EFT using bounds from relic density, Z invisible decay width, direct and indirect detection limits and collider constraints. Solutions below mZ are found for two operators. Others, around the electroweak scale or slightly above, are also compatible with all present limits.

Hidden charmonium decays of psi (nS) through charmed meson loops

We calculated transitions of the higher radial excited charmonia psi (nS) ~ ( n=3,4,5 ) to the orbital excited charmonium h_c(1P) with emission of one pion or eta meson. In calculations, the intermediate S- and P-wave charmed meson loops were considered in terms of the nonrelativistic effective field theory. The results indicate that the transitions of interest are dominated by the loops involving the s_l^P=(1/2)^+ charmed mesons, whereas the s_l^P=(1/2)^- charmed meson loops are of minor contributions. The partial decay widths of psi (nS) rightarrow h_c pi ^0 are of the order of 0.01–1 keV. For the case of psi (nS) rightarrow h_c eta , the partial decay widths are from 0.1 to 100 keV, implying the branching ratios from 10^{-5} to 10^{-3} . Moreover, the partial decay widths for psi (nS) rightarrow h_c eta are found to decrease as the eta - eta ' mixing angle increases. It is hoped that the present calculated results would be observed in the future experiments.

Combined analysis on nature of X(3960), chi _{c0}(3930), and X_0(4140)

In this work, a study of the D_s{bar{D}}_s interaction and its couplings to the channels D{bar{D}} and J/psi phi is performed in a quasipotential Bethe–Salpeter equation approach. The D_s^+{D}_s^- and D^+{D}^- invariant mass spectra in three-body B decays are investigated in order to understand the origin of X(3960), chi _{c0}(3930), and X_0(4140) structures reported at LHCb. With the help of effective Lagrangians, the potential kernel can be constructed with meson exchanges, from which the scattering amplitudes can be obtained. By inserting it into the three-body decay processes, the invariant mass spectra can be calculated with an additional Breit–Wigner resonance introduced. The D_s^+{D}_s^- invariant mass spectrum in the decay process B^+rightarrow D^+_sD^-_sK^+ is well reproduced, and the X(3960) structure can be explained as a molecular state from the D_s{bar{D}}_s interaction. The state also exhibits as a peak in the D^+{D}^- invariant mass spectrum in the decay B^+rightarrow D^+D^-K^+, however, it is too narrow to reproduce the experimental structure around 3930 MeV. The dip around 4140 MeV in the D_s^+{D}_s^- invariant mass spectrum can be reproduced by the additional resonance with interference effect. However, a small bump instead of a dip is produced from the D_s{bar{D}}_s-J/psi phi coupled-channel effect, which suggests that the X_0(4140) cannot be interpreted as the D_s{bar{D}}_s-J/psi phi coupling in the current model.

Search for a vector-like quark T′ → tH via the diphoton decay mode of the Higgs boson in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

A search for the electroweak production of a vector-like quark T′, decaying to a top quark and a Higgs boson is presented. The search is based on a sample of proton-proton collision events recorded at the LHC at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV, corresponding to an integrated luminosity of 138 fb−1. This is the first T′ search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet T′ states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a T′ quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength κT = 0.25 and a relative decay width Γ/MT′< 5%.

Collisional Broadening within a Hadronic Transport Approach

We explore the emergence of the collisional broadening of hadrons under the influence of different media using the hadronic transport approach SMASH (Simulating Many Accelerated Strongly interacting Hadrons), which employs vacuum properties and contains no a priori information about in-medium effects. In this context, we define collisional broadening as a decrease in the lifetime of hadrons, and it arises from an interplay between the cross-sections for inelastic processes and the available phase space. We quantify this effect for various hadron species, in both a thermal gas in equilibrium and in nuclear collisions. Furthermore, we distinguish the individual contribution of each process and verify the medium response to different vacuum assumptions; we see that the decay width that depends on the resonance mass leads to a larger broadening than a mass-independent scenario.

Molecular states in systems* *Supported by the Doctoral Program of Tian Chi Foundation of Xinjiang Uyghur Autonomous Region of China (51052300506), the NSFC and the Deutsche Forschungsgemeinschaftn(DFG, German Research Foundation) through the funds provided to the Sino-German Collaborative Research Center TRR110 “Symmetries and the Emergence of Structure in QCD” (NSFC 12070131001, DFG Project-ID 196253076 - TRR 110), the NSFC (11835015,

The possible hadronic molecules in systems with , and are investigated with interactions described by light meson exchanges. By varying the cutoff in a phenomenologically reasonable range of GeV, we find ten near-threshold (bound or virtual) states in the single-channel case. After introducing the coupled-channel dynamics of ----- systems, these states, except those below the lowest channels in each sector, move into the complex energy plane and become resonances in the mass range GeV. Their spin-parities and nearby thresholds are , , , , , , , , , and . The impact of the -term in the one-boson-exchange model on these states is presented. Setting GeV as an illustrative value, it is found that is a stable bound state (becoming unstable if the coupling to lower channels is turned on), and are physical resonances in cases where the -term is included or excluded, and the other seven states are physical resonances or "virtual-state-like" poles near thresholds, depending on whether the -term is included. In addition, the partial decay widths of the physical resonances are provided. These double-charm hidden-strangeness pentaquark states, as the partners of the experimentally observed and states, can be searched for in the final states in the future.

Search for tri-nucleon decays of ^{76}Ge in GERDA

We search for tri-nucleon decays of ^{76}Ge in the dataset from the GERmanium Detector Array (GERDA) experiment. Decays that populate excited levels of the daughter nucleus above the threshold for particle emission lead to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead to ^{73}Cu, ^{73}Zn, and ^{73}Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of ^{73}Ga to ^{73}Ge (stable). We search for the ^{73}Ga decay exploiting the fact that it dominantly populates the 66.7 keV ^{73m}Ga state with half-life of 0.5 s. The nnn-decays of ^{76}Ge that proceed via ^{73m}Ge are also included in our analysis. We find no signal candidate and place a limit on the sum of the decay widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime limit of 1.2times 10^{26} yr (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude.

The model for describing the width of double-gamma decay of the quadrupole state of spherical nuclei

We study the competitive γγ-decay of the state of an even-even spherical nucleus. An influence of the phonon-phonon coupling on the double γ-decay width is analysed within the microscopic model based on the Skyrme energy density functional. It is shown that the γγ-decay width is sensitive to the interaction of the one- and two-phonon configurations of the giant dipole resonance.

2-charge circular fuzz-balls and their perturbations

We perform a detailed study of perturbations around 2-charge circular fuzz-balls and compare the results with the ones obtained in the case of ‘small’ BHs. In addition to the photon-sphere modes that govern the prompt ring-down, we also find a branch of long-lived QNMs localised inside the photon-sphere at the (meta)stable minimum of the radial effective potential. The latter are expected to dominate late time signals in the form of ‘echoes’. Moreover, contrary to ‘small’ BHs, some ‘static’ tidal Love numbers are non-zero and independent of the mass, charges and angular momentum of the fuzz-ball. We rely on the recently established connection between BH or fuzz-ball perturbation theory and quantum Seiberg-Witten curves for mathcal{N} = 2 SYM theories, which in turn are related to Liouville CFT via the AGT correspondence. We test our results against numerical results obtained with Leaver’s method of continuous fractions or Breit-Wigner resonance method for direct integration and with the WKB approximation based on geodesic motion. In the probe approximation, we also exclude rotational super-radiance, due to the absence of an ergo-region, and absorption, due to the absence of a horizon.

Pair Production of Heavy Charged Gauge Bosons in pp Collisions at LHC

Abstract Two oppositely charged new heavy gauge boson pair production at the Large Hadron Collider (LHC), is presented in this paper. These bosons are known as W ′ boson due to the reason that it is the heavy version of Standard Model’s weak force carrier, the W boson. The production cross section and decay width in proton-proton (pp) collision at s = 8 TeV are calculated for different masses and coupling strengths of W ′ . Efficiencies for different signal regions and branching ratios for different decay channels are computed. In this study, the pair production ( W ′ + W ′ − ) is considered in emerging new physics as a result of pp collision at s = 8 TeV at the LHC with final state containing two tau (τ) leptons and two neutrinos (each W ′ decay to τ and its neutrino). The event selection efficiency similar to the CMS experiment is used for the mass of W ′ to set lower limits for different coupling strengths of W ′ and, the obtained results are presented in this work. For heavy gauge bosons, when coupling strength is similar to that of Standard Model’s W boson, the mass of W ′ below 445 GeV are excluded at a confidence level of 95%.

Spectroscopic behavior of fully heavy tetraquarks

Stimulated by the observation of the X(6900) from LHCb in 2020 and the recent results from CMS and ATLAS in the di-J/psi invariant mass spectrum, in this work we systematically study all possible configurations for the ground states of fully heavy tetraquark in the constituent quark model. By our calculation, we present their spectroscopic behaviors including binding energy, lowest meson–meson thresholds, specific wave function, magnetic moment, transition magnetic moment, radiative decay width, rearrangement strong width ratio, internal mass contributions, relative lengths between (anti)quarks, and the spatial distribution of four valence (anti)quarks. We cannot find a stable S-wave state for the fully heavy tetraquark system. We hope that our results will be valuable to further experimental exploration of fully heavy tetraquark states.

Analysis of the decay constants and form factors of pseudoscalar mesons in a dirac formalism

We investigate the weak leptonic and semileptonic decay widths of pseudoscalar light and heavy mesons in a Dirac formalism. We take relativistic-independent quark model of the form [Formula: see text], where [Formula: see text]. This is computed using the binding quark eigenfunction and taking the assumptions of a significant relationship between the quark and antiquark momenta inside the decaying meson in the rest frame. To calculate the decay constant [Formula: see text], decay width and branching fractions of pseudoscalar mesons, we employ the model parameters that we used earlier. The experimental findings and various similar models are in good agreement with our predictions such as [Formula: see text] and [Formula: see text]”. Finally, we calculate the form factors and branching fractions for the semileptonic [Formula: see text] decays [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]” and find reasonable agreement with the experimental results.

Analytical estimation of lifetime of quasi-bound states in iii-v semiconductors quantum well

The lifetime of electrons in the Quasi Bound States in a quantum well formed by III-V semiconductors has been calculated numerically by several researchers in the past. In this work, we obtain an analytical expression for the lifetime by finding the poles of the scattering matrix in small-width approximation. Airy functions which are solutions of the Schrödinger equation for triangular potentials are expanded asymptotically for large arguments and in power series for small arguments. A scattering problem for the triangular potential well is solved with the help of mixed boundary conditions to derive the expression for the decay width that further gives the net tunneling current from the quantum well. Heterostructures of III-V materials are modeled with triangular wells whose experimental measurements are in close approximation with the theoretical calculations presented in this paper. The analytically calculated decay width in this work is also compared with the reported values by different numerical methods and found in close agreement with them.

Bounds on lepton non-unitarity and heavy neutrino mixing

We present an updated and improved global fit analysis of current flavour and electroweak precision observables to derive bounds on unitarity deviations of the leptonic mixing matrix and on the mixing of heavy neutrinos with the active flavours. This new analysis is motivated by new and updated experimental results on key observables such as Vud, the invisible decay width of the Z boson and the W boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistic, which may present significant deviations from a χ2 distribution. The results are provided for three different Type-I seesaw scenarios: the minimal scenario with only two additional right-handed neutrinos, the next to minimal one with three extra neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrise via a generic deviation from a unitary leptonic mixing matrix. Additionally, we also analyze the case of generic deviations from unitarity of the leptonic mixing matrix, not necessarily induced by the presence of additional neutrinos. This last case relaxes some correlations among the parameters and is able to provide a better fit to the data. Nevertheless, inducing only leptonic unitarity deviations avoiding both the correlations implied by the right-handed neutrino extension as well as more strongly constrained operators is challenging and would imply significantly more complex UV completions.

First-principle calculation of the [formula omitted] decay width from lattice QCD

We perform a lattice QCD calculation of the ηc→2γ decay width using a model-independent method that requires no momentum extrapolation of the off-shell form factors. This method also provides a straightforward and simple way to examine the finite-volume effects. The calculation is accomplished using Nf=2 twisted mass fermion ensembles. The statistically significant excited-state effects are observed and eliminated using a multi-state fit. The impact of fine-tuning the charm quark mass is also examined and confirmed to be well-controlled. Finally, using three lattice spacings for the continuum extrapolation, we obtain the decay width Γηcγγ=6.67(16)stat(6)syst keV, which differs significantly from the Particle Data Group’s reported value of Γηcγγ=5.4(4) keV (2.9σ tension). We provide insight into the comparison between our findings, previous theoretical predictions, and experimental measurements.

Measuring inflaton couplings via primordial gravitational waves

We investigate the reach of future gravitational wave (GW) detectors in probing inflaton couplings with visible sector particles that can either be bosonic or fermionic in nature. Assuming reheating takes place through perturbative quantum production from vacuum in presence of classical inflaton background field, we find that the spectral energy density of the primordial GW generated during inflation becomes sensitive to inflaton-matter coupling. We conclude, obeying bounds from Big Bang Nucleosysthesis and Cosmic Microwave Background, that, e.g., inflaton-scalar couplings of the order of ~ \U0001d4aa(10−20) GeV fall within the sensitivity range of several proposed GW detector facilities. However, this prediction is sensitive to the size of the inflationary scale, nature of the inflaton-matter interaction and shape of the potential during reheating. Having found the time-dependent effective inflaton decay width, we also discuss its implications for dark matter (DM) production from the thermal plasma via UV freeze-in during reheating. It is shown, that one can reproduce the observed DM abundance for its mass up to several PeVs, depending on the dimension of the operator connecting DM with the thermal bath and the associated scale of the UV physics. Thus we promote primordial GW to observables sensitive to feebly coupled inflaton, which is very challenging if not impossible to test in conventional particle physics laboratories or astrophysical measurements.