Dominant Decay Mode Research Articles

Boosted four-top production at the LHC: A window to Randall-Sundrum or extended color symmetry

Scenarios seeking to address the issue of electroweak symmetry breaking often have heavy colored gauge bosons coupling preferentially to the top quark. Considering the bulk Randall-Sundrum as a typical example, we consider the prospects of the first Kaluza-Klein mode (G(1)) of the gluon being produced at the LHC in association with a tt¯ pair. The enhanced coupling not only dictates that the dominant decay mode would be to a tt¯ pair, but also to a very large G(1) width, necessitating the use of a renormalized G(1) propagator. This, along with the presence of large backgrounds (specially tt¯jj), renders a conventional cut-based analysis ineffective, yielding only marginal significances of only around 2σ. The use of machine learning (ML) techniques alleviates this problem to a great extent. In particular, the use of artificial neural networks helps us identify the most discriminating observables, thereby allowing a significance in excess of 4σ for G(1) masses of ∼4 TeV. Published by the American Physical Society 2024

Two-photon production of f0 and a0 resonances as hadronic molecules composed of two vector mesons

Ascribed as ρρ and K*K¯* molecular states, respectively, isoscalar f0(1500) and f0(1710) states are expected to have isovector partners, potentially identified as a0(1450) and a0(1710). The predicted dominant decay modes for these two a0 resonances are a0(1450)→ωππ and a0(1710)→ωππ,ϕππ. We estimate cross sections for two-photon production of these four resonances within hadronic molecular picture, and demonstrate that SuperKEKB’s luminosity is sufficient for their observation and more precise parameter measurements. Published by the American Physical Society 2024

Exploring the competition between α-decay and proton radioactivity: A comparative study of proximity potential formalisms

We have conducted a comprehensive and systematic study of the proton radioactivity and α-decay half-lives of neutron-deficient nuclei. This investigation involved the utilization of various Proximity potentials and also considered the incorporation of thermal effects. For the half-life calculations, we employed both temperature-independent and temperature-dependent interaction potentials. We observed that proton radioactivity serves as the dominant mode of decay for nuclides situated very close to the proton drip-line. We explored a universal curve that examines the correlation between the decimal logarithm of experimental half-lives and the negative decimal logarithm of the penetrability for both proton radioactivity and α-decay.

Heavy particle radioactivity of superheavy nuclei.

We investigated different decay modes such as heavy particle radioactivity (HPR), spontaneous fission (SF), alpha decay and beta-decay in superheavy (SH) region 104≤Z≤126. In HPR, different emissions from Zmin=28 to maximum heavy particle (HP) emission up to Zmax=Z-82 were considered. In the evaluation of Q-values, mass excess Weizsäcker-Skyrme 4+radial basis function (WS4+RBF) values were taken into account. The half-lives of cluster decay determined using modified generalised liquid drop model (MGLDM) and Coulomb and proximity potential model (CPPM) were in close agreement with the experimental results. The MGLDM produce less deviation compared with CPPM. The role of asymmetry effect, relative neutron excess, pairing effect and Coulomb effect on half-lives were studied. A band of neutron numbers from 193 to 200 shows extra stability against HPR. The HPR of 86Kr, 94Zr, 91Y and 96Mo is observed in the superheavy elements Z=118, 122-124 and 126. The dominant decay mode identified is compared with SF, alpha and beta± decay, the majority of decay chains end with the lead nuclei, which is also evident in supernova and galaxy spectrum. This study could be useful in nuclear astrophysics.

Theoretical predictions on cluster radioactivity of superheavy nuclei with Z = 119, 120* *Supported by the National Natural Science Foundation of China (12035011, 11975167, 11947211, 11905103, 11881240623, 11961141003), and by the National Key R&D Program of China (2018YFA0404403)

In this study, we investigate the cluster radioactivity (CR) of new superheavy elements with and 120 based on two successful theoretical methods with modified parameters: the density-dependent cluster model (DDCM) and unified decay formula (UDF). First, we employ the DDCM and UDF to accurately reproduce the experimental half-lives of cluster emissions, which demonstrates the high reliability of our theoretical methods. Then, we systematically predict the probable cluster modes of 293-311119 and 293-302120 as well as their corresponding decay energies and half-lives. The half-lives of cluster decay derived from the DDCM are consistent with those from the UDF. Therefore, our results reveal that the cluster emission of 8Be, emitted from the 119 and 120 isotopic chains, exhibits the minimum half-life for cluster emission, and hence, 8Be emission is considered the most probable cluster decay mode. Moreover, we explore the competition between α decay and CR and find that α decay may be the dominant decay mode against CR. Furthermore, the good linear relationship between the decay energy and the number of α particles within the emitted cluster is extended to the range of superheavy nuclei (SHN). We anticipate that our theoretical predictions for CR will provide valuable references for the experimental synthesis of new SHN.

Vectorlike leptons and long-lived bosons at the LHC

We study a renormalizable theory that includes a heavy weak-singlet vectorlike lepton, τ′, that decays into a pseudoscalar boson and a tau lepton. We show that this can be the dominant decay mode of τ′ provided the pseudoscalar couplings deviate from the case of a Nambu-Goldstone boson. For a range of parameters, the pseudoscalar is long-lived, and mainly decays into a photon pair at one loop, or into a tau pair at tree level. Electroweak production of τ′+τ′− leads to a rich phenomenology at colliders, including signals with many taus or photons. We analyze in detail the LHC signal involving two prompt taus and two displaced photon pairs. Particularly interesting is the case where the pseudoscalar has a decay length of a few meters and thus would typically deposit energy in the muon chambers of the CMS or ATLAS detectors.

Decay Modes and Half-Life of 265–282Ds Isotopes

The decay modes and half-lives of superheavy 265–282Ds isotopes have been investigated by using Relativistic Mean Field (RMF) model with density-dependent point-coupling and density-dependent meson-exchange functional. The potential energy surfaces as a funtion of deformation parameters ( $$\beta ,\gamma$$ ) for the considered Ds nuclei have been obtained by using a triaxially deformed RMF model calculations for the investigation of their ground-state shapes and binding energies. The computed ground-state binding energy values of given Ds isotopes have been used for calculations of Q values of the alpha ( $$\alpha$$ ), beta-plus/electron capture ( $$\beta ^{+}$$ /EC), beta-minus ( $$\beta ^{-}$$ ) and spontaneous fission (SF) decay modes. The dominant decay modes and half-lives of 265–282Ds isotopes have been predicted by using the computed Q-values and some empirical formulas. The results of the present study demonstrate that the 265–282Ds isotopes are well deformed, with prolate configuration in their ground-states. Our estimations for decay modes and half-lives are consistent with available experimental data.

Theoretical predictions for α-decay chains and cluster radioactivity of superheavy nuclei with Z = 126

Theoretical predictions of [Formula: see text]-decay properties of several isotopes of the superheavy nucleus of [Formula: see text] [Formula: see text] and their consecutive [Formula: see text]-decay chains are presented. Based on the double-folding model, the [Formula: see text]–daughter interaction potential is constructed microscopically using a realistic M3Y–Paris nucleon–nucleon (NN) interaction. The [Formula: see text]-decay half-lives are computed for both spherical and deformed shapes of daughter nuclei within the density-dependent cluster model. The effect of deformation is found to decrease the [Formula: see text]-decay half-lives compared to spherical shapes. The calculated [Formula: see text]-decay half-lives are in satisfactory agreement with their counterparts using other theoretical methods. The prediction of the dominant decay mode for the isotopes [Formula: see text], which have not yet been experimentally synthesized, is presented through the competition between [Formula: see text]-decay and spontaneous fission. We have found that the isotopes [Formula: see text] survive fission and have relatively long half-lives which span the order [Formula: see text]–[Formula: see text]. Moreover, the correlation between the logarithm of the preformation probability deduced from the cluster formation model and the fragmentation potential for even–even [Formula: see text] isotopes is elucidated showing a negative linear relation. The feasibility of cluster emission from the superheavy isotope [Formula: see text] is investigated using different theoretical approaches. The predictions can provide useful guidance for future experimental researches.

Detecting Heavy Neutral SUSY Higgs Bosons Decaying to Sparticles at the High-Luminosity LHC

In supersymmetry (SUSY) models with low electroweak naturalness (natSUSY), which have been suggested to be the most likely version of SUSY to emerge from the string landscape, higgsinos are expected at the few hundred GeV scale, whilst electroweak gauginos inhabit the TeV scale. For TeV-scale heavy neutral SUSY Higgs bosons H and A, as currently required by LHC searches, the dominant decay modes of H,A are gaugino plus higgsino provided these decays are kinematically open. The light higgsinos decay to soft particles, so are largely invisible, whilst the gauginos decay to W, Z or h plus missing transverse energy (ET). Thus, we examine the viability of H,A→W+ET, Z+ET and h+ET signatures at the high luminosity LHC (HL-LHC) in light of large standard model (SM) backgrounds from (mainly) tt¯, VV and Vh production (where V=W,Z). We also examine whether these signal channels can be enhanced over backgrounds by requiring the presence of an additional soft lepton from the decays of the light higgsinos. We find significant regions in the vicinity of mA∼1–2 TeV of the mA vs. tanβ plane, which can be probed at the high luminosity LHC, using these dominant signatures by HL-LHC at 5σ and at the 95% confidence level (CL).

A Systematic Study of Proton Decay in Superheavy Elements

We have studied the proton decay in almost all superheavy nuclei with atomic number Z = 104–126. We have calculated the energy released during the proton decay (QP), penetration factor (P), normalization factor (F), and the proton decay half-lives. The latter are also longer than that of other decay modes such as the alpha decay and spontaneous fission. The competition of the proton decay with different decay modes reveals that the proton decay is not the dominant decay mode in the superheavy nuclei region. This means that superheavy nuclei are stable against the proton decay.

Discovery prospects of a vectorlike top partner decaying to a singlet boson

The possibility of a vectorlike top partner decaying to a new colourless weak-singlet scalar or pseudoscalar has attracted some attention in the literature. We investigate the production of a weak-singlet charge-$2/3$ $T$ quark that can decay to a spinless boson ($\Phi$) and a top quark at the LHC. Earlier, in 2203.13753, we have shown that in a large part of the parameter space, the $T\to t\Phi$ and the loop-induced $\Phi \to gg$ decays become the dominant decay modes for these particles. Here, we investigate the discovery prospects of the $T$ quark in this region through the above decays. In particular, we focus on the $pp\to TT\to (t\Phi)(t\Phi)\to (t(gg))\,(t(gg))$ channel. Separating this signal from the huge Standard Model background is a challenging task, forcing us to employ a multivariate machine-learning technique. We find that the above channel can be a discovery channel of the top partner in the large part of the parameter space where the above decay chain dominates. Our analysis is largely model-independent, and hence our results would be useful in a broad class of new physics models.

CDF W -boson mass and muon g−2 in a type-X two-Higgs-doublet model with a Higgs-phobic light pseudoscalar

The recent measurement of the $W$ boson mass by the CDF collaboration adds an anomaly to the longstanding discrepancy in the muon anomalous magnetic moment, $\mathrm{\ensuremath{\Delta}}{a}_{\ensuremath{\mu}}$. Although type-X in the two-Higgs-doublet model provides an attractive solution to $\mathrm{\ensuremath{\Delta}}{a}_{\ensuremath{\mu}}$ through a light pseudoscalar $A$, the model confronts the exotic Higgs decays of $h\ensuremath{\rightarrow}AA$ and the lepton flavor universality data in the $\ensuremath{\tau}$ and $Z$ decays. To save the model, we propose that the light pseudoscalar be Higgs-phobic. Through the random scanning over the entire parameter space, we perform a comparative study of the Higgs-phobic type-X with and without the CDF ${m}_{W}$ measurement, called the CDF and PDG cases, respectively. Both cases can explain the two anomalies as well as all the other constraints, but have significant differences in the finally allowed parameter space. For example, a small region with almost degenerate masses of new Higgs bosons around 100 GeV is allowed only in the PDG case. The cutoff scale of the model is also studied via the analysis of renormalization group equations, which reaches up to ${10}^{5}\text{ }\text{ }\mathrm{GeV}$ (${10}^{7}\text{ }\text{ }\mathrm{GeV}$) in the CDF (PDG) case. Since the dominant decay modes are $A\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\tau}$, $H\ensuremath{\rightarrow}ZA$, and ${H}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}A$ in most of the viable parameter space, we propose the $4\ensuremath{\tau}+V{V}^{\ensuremath{'}}$ states as the golden discovery channel at the LHC.

Comprehensive study of the light charged Higgs boson in the type-I two-Higgs-doublet model

In the type-I two-Higgs-doublet model, existing theoretical and experimental constraints still permit the light charged Higgs boson with a mass below the top quark mass. We present a complete roadmap for the light charged Higgs boson at the LHC through the comprehensive phenomenology study, focusing on the normal scenario where the lighter \textit{CP}-even Higgs boson is the observed Higgs boson. In type-I, it is challenging to simultaneously accommodate the light mass of the charged Higgs boson and the constraints from theory, electroweak precision data, Higgs data, $b\to s \gamma$, and direct search bounds. Consequently, the parameter space is extremely curtailed, which predicts somewhat definite phenomenological signatures. We find that the mass of the pseudoscalar Higgs boson, $M_A$, is the most crucial factor in the phenomenology of the charged Higgs boson. If $M_A$ is light, the charged Higgs boson decays mainly into $A W^\pm$. When $M_A$ is above the $A W^\pm$ threshold, the dominant decay mode is into $ \tau^\pm \nu$. Over the whole viable parameter space, we study all the possible production and decay modes of charged Higgs bosons at the LHC, and suggest three efficient channels: (i) $pp \to H^+ H^-\to [\tau \nu] [\tau \nu]$; (ii) $pp \to HA/HH/AA \to H^\pm W^\mp H^\pm W^\mp \to [\tau \nu] [\tau \nu] W W$; (iii) $pp \to H^+ H^-\to [b \bar b W ] [b \bar b W ] $. Based on the sophisticated signal-background analyses including detector simulation, we showed that the significance of the first final state is large, that of the second one is marginal around three, but the third one suffers from huge $t\bar t$ related backgrounds.

P c resonances in the compact pentaquark picture

P c resonances are studied in the approach of quark model and group theory. It is found that there are totally 17 possible pentaquark states with the quark contents (q are u and d quarks; Q is c quark) in the compact pentaquark picture, where the hidden charm pentaquark states may take the color singlet–singlet and color octet–octet configurations. The theoretical results of partial decay widths of the pentaquark states show that open charm channels are the dominant decay modes for almost all hidden charm pentaquark states, but there are four pentaquark states which decay through the pJ/ψ channel with sizable partial decay widths.

New Options for SUSY-Kind Dark Matter

In the conventional cosmology masses of the stable supersymmetric relics, candidates for the dark matter (DM) particles, should be typically below 1 TeV. This is in conflict with the LHC bounds on the low energy SUSY. However, in $$R^{2}$$ -gravity the masses of the stable particles with the interaction strength typical for SUSY could be much higher depending upon the dominant decay mode of the scalaron. We discuss the bounds on the masses of DM particles for the following dominant decay modes: to minimally coupled massless scalars, to massive fermions, and to gauge bosons.

Probable decay modes of even–even superheavy nuclei

Cluster-decay half-lives () of even–even nuclei are calculated employing interaction potential involving Coulomb and proximity potentials and, the obtained results are compared with the experimental ones. In order to study cluster radioactivity in even–even superheavy nuclei (SHN), we evaluate the required disintegration energies (Q c -values) utilizing periodic-orbit theory within microscopic-macroscopic formalism and hence, predict the logarithmic values of 's for even–even 298−312Og and 296−310120 nuclei. Among various isotopes of daughter nuclei, products produced with minimum value of Gibbs free energy are chosen for our investigation. Also, an analysis of the branching ratios enables us to determine the dominant mode of decay among α − decay, spontaneous fission (SF) and cluster-decay in these SHN. The emissions of 90Kr from 298Og and 94Sr cluster from 296,298120 SHN are found to be the dominant mode of decay. Our results are in agreement with those obtained using UDL method except for few cases. We believe that this work can play a significant role in the experiments leading to identification of exotic nuclei.

Radioactivity of even–even superheavy nuclei with Z = 122, 124 and 126

Employing Coulomb and proximity potentials, cluster-decay half-lives ([Formula: see text]) of even–even nuclei had been calculated and, the obtained results are compared with the experimental ones. To investigate cluster radioactivity in superheavy nuclei (SHN), we determine the required disintegration energies ([Formula: see text]-values) utilizing periodic-orbit theory within microscopic-macroscopic formalism and hence, predict the logarithmic values of [Formula: see text] for even–even SHN with [Formula: see text], 124 and 126. Among various isotopes of daughter nuclei, products produced with minimum value of Gibbs free energy are chosen for our investigation. Moreover, study of the branching ratios would make us to find the dominant mode of decay among [Formula: see text]-decay, spontaneous fission (SF) and cluster-decay in these SHN. Mostly, the emissions of Kr-, Sr-, Zr- and Mo-clusters from these superheavy nuclei are found to be the dominant modes of decay which can be attributed to strong shell effects in the neighborhood of [Formula: see text] region. Our results are in agreement with those obtained using UDL method except for few cases. We believe that this work can play a significant role in the study of decay properties of superheavy nuclei.

Studies on the decay modes of superheavy nuclei with Z = 120

A study on the competition between alpha-decay and spontaneous fission (SF) of the Z = 120 isotopes with 283 ≤ A ≤ 350 is performed in this paper. The alpha-decay half-lives are evaluated using the modified generalized liquid drop model (MGLDM). The SF half-lives are calculated within the shell-effect-dependent formula. It is found that the dominant decay mode of 294,295,297,298,301-304,308120 is alpha-decay and the half-lives fall within the experimental limit (>1 μs). Then the decay properties of the alpha-decay chain of 294,295,297,298,301-304,308120 are predicted within the MGLDM and the shell-effect-dependent formula. These predictions are helpful for searching and identifying the new elements in future. Finally, the possibility of the cluster radioactivity of the Z = 120 isotopes is discussed within the MGLDM. By analyzing the competition between the cluster radioactivity and alpha-decay, it is found that the possibility of the cluster radioactivity is much smaller than the corresponding alpha-decay.

Competition between weak and α -decay modes in superheavy nuclei

The competition between $\ensuremath{\alpha}$- and ${\ensuremath{\beta}}^{+}/\text{EC}$-decay modes is studied systematically in nuclei along the $\ensuremath{\alpha}$-decay chains following the synthesis of superheavy nuclei with $Z=119$ and $Z=120$. A microscopic approach based on deformed self-consistent Hartree-Fock mean-field calculations with Skyrme forces and pairing correlations is used to describe the ${\ensuremath{\beta}}^{+}$ and electron capture weak decays, whereas the $\ensuremath{\alpha}$ decay is estimated from existing phenomenological expressions. It is shown that $\ensuremath{\alpha}$ decay is in most cases the dominant decay mode, but interesting instances are identified where the half-lives are comparable, opening the possibility of new pathways towards more neutron-rich nuclei in this region.

Proton radioactivity and α-decay of neutron-deficient nuclei

Proton radioactivity and α-decay half-lives of neutron-deficient nuclei have been systematically studied. The proton-nucleus interaction potential is developed by single folding the density distribution of the daughter nuclei with the effective M3Y-Paris nucleon-nucleon (NN) interaction. The penetrability is calculated with the Wentzel-Kramers-Brillouin approximation. The applicability of the universal decay law on the proton decay half-lives has been examined and a new set of parameters has been identified. The competition between α-decay and proton radioactivity of neutron-deficient nuclei has been investigated. The proton radioactivity is found to be the dominant mode of decay for nuclides located very close to the proton drip-line. The effect of using different microscopic proton and neutron density distributions on the half-lives for these two decay modes is studied. It is found that the calculated half-lives with the microscopic densities that obtained from the self-consistent Hartree–Fock-Bogoliubov method successfully reproduce the experimental data. The impact of nuclear deformation on the half-lives is investigated for these two decay modes. The influence of nonlocality through the finite-range exchange part of the NN interaction on the α-decay process is elucidated. Our theoretical calculations have been confirmed experimentally and satisfactory agreement has been achieved.