Dominant Decay Mode Research Articles

Possible candidate of the0+ss¯ss¯state

The possibility of the $0^+$ $\eta\eta$ resonance $f_0(2100)$ as a candidate of the $Q^2\bar{Q}^2$ state $C^{ss}(36)$ is explored. The $\eta\eta$ channel of $f_0(2100)$ is the dominant decay mode, $\eta\eta'$ channel has less decay rate, the decay rate of the $\eta'\eta'$ channel is very small. The $\pi\pi,\;K\bar{K},\;4\pi$ modes are at next leading order in $N_C$ expansion. Other possible decay modes are discussed.

Dynamics of Ca40,48+238U→278,286112⁎ reactions across the Coulomb barrier using dynamical cluster decay model

Abstract The role of deformations and related orientations (optimum or compact) is investigated in reference to dynamics of Ca 40 , 48 + 238 U → 278 , 286 112 ⁎ reactions using dynamical cluster decay model (DCM). The use of quadrupole and hexadecapole deformations in the decay of compound system suggest that the degree of compactness changes with addition of higher order deformations. The decay cross-sections are calculated in reference to the available data, including β 2 -static deformations within ‘optimum’ orientation approach. The comparative analysis of spherical, β 2 -static and dynamic alongwith β 4 -static deformations is investigated at comparable center of mass energy of 230 MeV for both nuclei. To address the specific role of optimized orientations in the decay of 112 ⁎ 278 and 112 ⁎ 286 nuclei, the calculations are done using equatorial compact and polar elongated orientations. Using hot equatorial collisions, symmetric fission is observed as the dominant decay mode across the barrier, which otherwise becomes asymmetric for cold elongated approach. The calculated cross-sections match nicely with experimental data using hot configuration but the same are overestimated for the use of cold (polar) orientation approach at deep sub-barrier region. This overestimation in the deep sub-barrier region may be associated with the quasi-fission decay channel. The contribution of QF in both 112 ⁎ 278 and 112 ⁎ 286 nuclei are predicted through the overestimated cross-sections being more for neutron-deficient 112 ⁎ 278 nucleus, in agreement with experimental results. Larger barrier modification Δ V B is observed at sub-barrier energies for both isotopes of Z = 112 nucleus. Also the contribution of Δ V B at lower incident energies is relatively higher for cold elongated polar configuration as compared to hot compact equatorial configuration, causing overestimation of cross-section for the use of cold approach.

Measuring SUSY quartics from stop decays

In supersymmetric theories, there is a scalar quartic related to the top and bottom yukawas that gives LHC observable decays of the stop or sbottom. After electroweak symmetry breaking, this quartic induces the decay of the stop (sbottom) to a charged Higgs and the sbottom (stop) without allowing for the corresponding channel involving the W boson. Unlike other scalar quartics, this scalar quartic is measurable at the LHC and for compressed spectra may even be the discovery channel for the stop or sbottom. Observing this decay and measuring the value of the quartic interaction would give direct evidence that the underlying theory is supersymmetric as only a fermionic symmetry can relate a scalar quartic to a yukawa interaction. This decay pathway is explored and situations where it can be the dominant decay mode for either the stop or the sbottom are highlighted. Measurement of this decay mode at the LHC would unambiguously show that the underlying theory of nature was supersymmetric.

Pinning down Higgs triplets at the LHC

Extensions of the Standard Model Higgs sector involving weak isotriplet scalars are not only benchmark candidates to reconcile observed anomalies of the recently discovered Higgs-like particle, but also exhibit a vast parameter space, for which the lightest Higgs' phenomenology turns out to be very similar to the Standard Model one. A generic prediction of this model class is the appearance of exotic doubly charged scalar particles. In this paper we adapt existing dilepton+missing energy+jets measurements in the context of SUSY searches to the dominant decay mode $H^{\pm\pm}\to W^\pm W^\pm$ and find that the LHC already starts probing the model's parameter space. A simple modification towards signatures typical of weak boson fusion searches allows us to formulate even tighter constraints with the 7 TeV LHC data set. A corresponding analysis of this channel performed at 14 TeV center of mass energy will constrain the model over the entire parameter space and facilitate potential $H^{\pm\pm}\to W^\pm W^\pm$ discoveries.

Same-sign dileptons from colored scalars in the flavorful top-coloron model

In this paper we study the phenomenology of color-octet and color-singlet scalars in the flavorful Top-Coloron model. We discuss the relevant production mechanisms at hadron colliders and the dominant decay modes, highlighting the most promising signatures for discovery, and derive bounds on the masses of the new scalars from LHC and Tevatron data. Of particular interest is the case in which color-octet scalars are pair produced and each decay to t cbar or tbar c, leading to a same-sign-dilepton final state. LHC data places a lower limit of 440 GeV on the octet mass in this scenario. The case of an octet lighter than the top, where the octet only decays into jets, has been tested by the Tevatron, which excludes the mass region from 50 to 125 GeV. The 8 TeV LHC is not yet sensitive to the observation of the color-singlet states, which are produced at rates much smaller than the octets. Nevertheless, the color-singlet pseudoscalar can be discovered at the 14 TeV LHC by analyzing the channel where it is produced from the decay of a color-octet vector boson.

Rotational 2+ states of superheavy elements in the Skyrme-Hartree–Fock–Bogoliubov model

The Skyrme-Hartree–Fock–Bogoliubov calculations of the energies of first 2+ rotational states of deformed superheavy (SH) elements in the region of 108 ⩽ Z ⩽ 126 and 148 ⩽ N ⩽ 180 are reported. The results agree well in the case of fermium isotopes after a proper scaling of the moment of inertia. The scaling factor equals 1.3. The extension of the model to the region of SH elements gives a possibility of better estimation of the Q-values of α-decay, which is a dominant decay mode of SH elements.

Dark radiation constraints on mixed Axion/Neutralino dark matter

Recent analyses of CMB data combined with the measurement of BAO and H0show that dark radiation — parametrized by the apparent number of additional neutrinos ΔNeff contributing to the cosmic expansion —is bounded from above by about ΔNeff≲1.6 at 95% CL. We consider the mixed axion/neutralino cold dark matter scenariowhich arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by hadronic axions with a concommitant axion(a)/saxion(s)/axino(ã) supermultiplet.Our new results include improved calculations of thermal axion and saxion production and include effects of saxion decay to axinos and axions. We show that the above bound on ΔNeff is easily satisfied if saxions are mainlythermally produced and mLSP < mã≲ms. However, if the dominantmechanism of saxion production is through coherent oscillations, the CMB dataprovides a strong bound on saxion production followed by saxion decays to axions.Furthermore we show that scenarios with mixed neutralino/axion dark matter are highlyconstrained by combined CMB, BBN and Xe-100 constraints. In particular,supersymmetric models with a standard overabundance of neutralino dark matterare excluded for all values of the Peccei-Quinn breaking scale.Next generation WIMP direct detection experiments may be able to discover or exclude mixedaxion-neutralino CDM scenarios where s → aa is the dominant saxion decay mode.

Cooperative decay rate and cooperative Lamb shift from a nanospherical configuration of two adjoining atomic species

The eigenmodes of a nanosphere configuration where the core is an ensemble of two-level atoms with resonance frequency ${\ensuremath{\omega}}_{C}$, and the shell is an ensemble of two-level atoms but with shifted resonant frequency ${\ensuremath{\omega}}_{B}$ are obtained for different values of the ratio of the core radius to the shell outer radius as function of $({\ensuremath{\omega}}_{C}\ensuremath{-}{\ensuremath{\omega}}_{B})$. I show that the eigenmodes belong to one of two branches. The dominant decay mode for superradiant emission may belong to either branch, depending on the system's parameters. In instances of configurations where the cooperative decay rate values for the two branches become equal, the cooperative exponential amplification (decay) is accompanied by temporal oscillations.

Discovering nonstandard Higgs bosons in the H →ZA channel decay to multileptons

In this article we consider the possibility of observing nonstandard Higgs bosons in the H -> Z A -> Z tau+ tau- channel. We present three benchmark scenarios in the NMSSM where H -> ZA is the dominant decay mode for one of the nonstandard Higgs bosons while the lightest CP-even Higgs is Standard Model like. Using the latest CMS multilepton analysis based on 7 TeV LHC data, we put limits on the signal cross-section, which constrain leptophilic scenarios. Projecting to future LHC analyses with improvements in background modeling, we show that with O(30) fb^{-1} of data, such a multilepton analysis is very close to constraining our NMSSM benchmarks. As we illustrate with a toy model, for light A masses, the large boost of the A makes it inefficient to select two hadronic taus, since isolation and the transverse momenta are in tension. This efficiency could be improved by including boosted di-tau jets as an object in future multilepton analyses. We also discuss different methods to confirm this scenario by reconstruction of the m_H and m_A masses. In particular we consider the transverse mass distribution, collinear mass distribution and an analytical solution using trial masses.

ELECTROWEAK SYMMETRY BREAKING AND THE HIGGS BOSON: CONFRONTING THEORIES AT COLLIDERS

In this review, we discuss methods of parsing direct information from collider experiments regarding the Higgs boson and describe simple ways in which experimental likelihoods can be consistently reconstructed and interfaced with model predictions in pertinent parameter spaces. We review prevalent scenarios for extending the electroweak symmetry breaking sector and emphasize their predictions for nonstandard Higgs phenomenology that could be observed in large hadron collider (LHC) data if naturalness is realized in particular ways. Specifically we identify how measurements of Higgs couplings can be used to imply the existence of new physics at particular scales within various contexts. The most dominant production and decay modes of the Higgs-like state observed in the early data sets have proven to be consistent with predictions of the Higgs boson of the Standard Model, though interesting directions in subdominant channels still exist and will require our careful attention in further experimental tests. Slightly anomalous rates in certain channels at the early LHC have spurred effort in model building and spectra analyses of particular theories, and we discuss these developments in some detail. Finally, we highlight some parameter spaces of interest in order to give examples of how the data surrounding the new state can most effectively be used to constrain specific models of weak scale physics.

Heavy neutrino decays at MiniBooNE

It has been proposed that a sterile neutrino \nu_h with m_h \approx 50 MeV and a dominant decay mode (\nu_h -> \nu\gamma) may be the origin of the experimental anomaly observed at LSND. We define a particular model that could also explain the MiniBooNE excess consistently with the data at other neutrino experiments (radiative muon capture at TRIUMF, T2K, or single photon at NOMAD). The key ingredients are (i) its long lifetime (\tau_h\approx 3-7x10^{-9} s), which introduces a 1/E dependence with the event energy, and (ii) its Dirac nature, which implies a photon preferably emitted opposite to the beam direction and further reduces the event energy at MiniBooNE. We show that these neutrinos are mostly produced through electromagnetic interactions with nuclei, and that T2K observations force BR(\nu_h -> \nu_\tau\gamma) \le 0.01 \approx BR(\nu_h -> \nu_\mu\gamma). The scenario implies then the presence of a second sterile neutrino \nu_{h'} which is lighter, longer lived and less mixed with the standard flavors than \nu_h. Since such particle would be copiously produced in air showers through (\nu_h -> \nu_{h'}\gamma) decays, we comment on the possible contamination that its photon-mediated elastic interactions with matter could introduce in dark matter experiments.

Stability of superheavy nuclei against α-decay and spontaneous fission

The stability of superheavy nuclei is mainly determined by the competition between alpha-decay and spontaneous fission. We investigate the half-lives of both alpha-decay and spontaneous fission for the heaviest nuclei with proton numbers up to Z = 121. The agreement between theoretical half-lives and available experimental data is fairly well for the superheavy nuclei. Enhanced stability against spontaneous fission is found for the Z = 119 and Z = 120 isotopic chains, which are of current experimental interests, alpha-Decay is predicted to be the dominating decay mode for the Z = 119 and Z = 120 isotopes with estimated half-lives ranging from microseconds to milliseconds. (c) 2012 Elsevier B.V. All rights reserved.

DECAYS OF FOURTH GENERATION BOUND STATES

We consider the decay modes of the heavy [Formula: see text] bound states originating from Higgs boson exchange between quark–antiquark pair. In case of a small coupling between the fourth and lower generation the main decay mode is [Formula: see text] annihilation. We show that for a vector state the dominant decay modes are Higgs-gamma and Higgs-Z decays, while for a pseudoscalar state the strong two-gluon decay mode dominates. The bound states are very narrow. The ratio of the total width to the binding energy is less than 1% if we are not extremely close to the critical quark mass where the binding energy is very small. The discussed decay modes exist for any fermion–antifermion bound states including heavy leptons and heavy neutrinos if their masses are high enough to form a bound state due to attractive Higgs boson exchange potential.

Search for a heavy vector boson decaying to two gluons inpp¯collisions ats=1.96 TeV

We present a search for a new heavy vector boson $Z'$ that decays to gluons. Decays to on-shell gluons are suppressed, leading to a dominant decay mode of $Z' \rightarrow g^*g$. We study the case where the off-shell gluon $g^*$ converts to a pair of top quarks, leading to a final state of $t\bar{t}g$. In a sample of events with exactly one charged lepton, large missing transverse momentum and at least five jets, corresponding to an integrated luminosity of 8.7 fb$^{-1}$ collected by the CDF II detector, we find the data to be consistent with the standard model. We set upper limits on the production cross section times branching ratio of this chromophilic $Z'$ at 95% confidence level from 300 fb to 40 fb for $Z'$ masses ranging from 400 GeV$/c^2$ to 1000 GeV$/c^2$, respectively.

Absolute decay width measurements in 16O

The reaction 126C(63Li, d)168O* at a 6Li bombarding energy of 42 MeV has been used to populate excited states in 16O. The deuteron ejectiles were measured using the high-resolution Munich Q3D spectrograph. A large-acceptance silicon-strip detector array was used to register the recoil and break-up products. This complete kinematic set-up has enabled absolute α-decay widths to be measured with high-resolution in the 13.9 to 15.9 MeV excitation energy regime in 16O; many for the first time. This energy region spans the 14.4 MeV four-α breakup threshold. Monte-Carlo simulations of the detector geometry and break-up processes yield detection efficiencies for the two dominant decay modes of 40% and 37% for the α+12C(g.s.) and a+12C(2+1) break-up channels respectively.

General MSSM signatures at the LHC with and withoutR-parity

We present the possible signatures appearing in general realizations of the minimal supersymmetric standard model based on 14 unrelated mass parameters at the supersymmetry scale. The parameters of the general minimal supersymmetric standard model are reduced by assuming a degeneracy of the sfermions of the first two generations with the same quantum numbers. We also assume no mass splitting between neutral and charged Higgsinos. We do allow for separate soft breaking terms for the third-generation sfermons. We consider all possible resulting $14!\ensuremath{\approx}9\ifmmode\times\else\texttimes\fi{}{10}^{10}$ relevant mass orderings and check for the dominant decay cascades and the corresponding collider signatures. In determining the dominant decay modes we assume that mixing between sparticles is subdominant. As preferred signatures, we consider charged leptons, missing transverse momentum, jets, and $W$, $Z$ or Higgs bosons. We include also the cases of bi- and trilinear $R$-parity violation and show that specific signatures can be used to distinguish the different scenarios.

Searching forZ′bosons decaying to gluons

The production and decay of a new heavy vector boson, a chromophilic ${Z}^{\ensuremath{'}}$ vector boson, is described. The chromophilic ${Z}^{\ensuremath{'}}$ couples only to two gluons, but its two-body decays are absent, leading to a dominant decay mode of ${Z}^{\ensuremath{'}}\ensuremath{\rightarrow}q\overline{q}g$. The unusual nature of the interaction predicts a cross-section which grows with ${m}_{{Z}^{\ensuremath{'}}}$ for a fixed coupling and an accompanying gluon with a coupling that rises with its energy. We study the $t\overline{t}g$ decay mode, proposing distinct reconstruction techniques for the observation of an excess and for the measurement of ${m}_{{Z}^{\ensuremath{'}}}$. We estimate the sensitivity of current experimental datasets.

The Strong Decay Properties of the 1−+Hybrid Mesons

We calculate the coupling constants of the decay modes 1 + ! ,f1 , b1 , , 0 , a1 , f1 within the framework of the light-cone QCD sum rule. Then we cal- culate the partial widths of these decay channels, which di er greatly from the existing calculations using phenomenological models. For the isovector 1 + state, the dominant decay modes are ; f1 . For its isoscalar partner, its dominant decay mode is a1 . We also discuss the possible search of the 1 + state at BESIII, for example through the decay chains J= ( 0 )! 1 + or J= ( 0 )! 1 + where 1 can be reconstructed through the decay modes 1 ! ! + 0 or 1 ! f1(1285) 0 . Hopefully the present work will be helpful to the experimental establishment of the 1 + hybrid meson.

Single vectorlike quark production at the LHC

A gluon resonance G of mass below 1 TeV could be the origin of the t t ¯ forward–backward asymmetry observed at the Tevatron provided that new decay modes G → q Q ¯ , with q a standard quark and Q its massive excitation, make G broad enough. We consider all the different cases, with q the top, the bottom or a light quark and dominant decay modes Q → W q ′ or Q → Z q . We show that current experimental searches are unable to probe the model, but that minimal departures from these analyses can explore a large region of its parameter space for the current LHC luminosity. This includes the challenging case with the new quarks decaying mostly into light quark flavors. In some channels not only the heavy quark but also the massive gluon can be reconstructed, which would stablish the origin of the t t ¯ asymmetry. Similar analyses can be applied to more general models with new massive gluons and vectorlike quarks.

Photoproduction of neutral pions off protons

Photoproduction of neutral pions has been studied with the CBELSA/TAPS detector in the reaction $\gamma p\to p\pi^0$ for photon energies between 0.85 and 2.50 GeV. The $\pi^0$ mesons are observed in their dominant neutral decay mode: $\pi^0\to\gamma\gamma$. For the first time, the differential cross sections cover the very forward region, $\theta_{\rm c.m.}<60^\circ$. A partial-wave analysis of these data within the Bonn-Gatchina framework observes the high-mass resonances $G_{17}$(2190), $D_{13}$(2080), and $D_{15}$(2070).