Dominant Decay Mode Research Articles

INVISIBLE HIGGS IN WEAK BOSONS ASSOCIATIVE PRODUCTION WITH HEAVY QUARKS AT LHC: PROBING MASS AND WIDTH

New physics coupled to the Higgs boson may hide it in the standard decay channels to be investigated at LHC. We consider the models where new invisible dominant decay modes of the Higgs boson are responsible for this hiding. We propose to study at LHC the weak boson production associated with heavy quarks: our analysis revealed that boson pair invariant mass distribution is sensitive to both mass and width of the invisible Higgs boson, if it is not too far from the weak boson pair threshold. We present tree-level results for the most relevant cases of top quarks and of bottom quarks in Standard Model extensions with large b-quark Yukawa coupling. We argue that QCD corrections do not spoil these results allowing for unambiguous extraction of the Higgs boson mass and width from the analysis of large enough amount of data.

Heavy octets and Tevatron signals with three or four b jets

Hypothetical color-octet particles of spin 0, pair-produced at hadron colliders through their QCD coupling, may lead to final states involving three or four b jets. We analyze kinematic distributions of the 3b final state that differentiate the scalar octets from supersymmetric Higgs bosons. Studying the scalar sector that breaks an SU(3) \times SU(3) gauge symmetry down to the QCD gauge group, we find that the scalar octet is resonantly produced in pairs via a spin-1 octet (coloron). A scalar octet of mass in the 140 - 150 GeV range can explain the nonstandard shape of the b-jet transverse energy distributions reported by the CDF Collaboration, especially when the coloron mass is slightly above twice the scalar mass. The dominant decay mode of the scalar octet is into a pair of gluons, so that the production of a pair of dijet resonances is large in this model, of about 40 pb at the Tevatron. Even when a W boson is radiated from the initial state, the inclusive cross section for producing a dijet resonance near the scalar octet mass remains sizable, around 0.15 pb.

Long lived fourth generation and the Higgs

A chiral fourth generation is a simple and well motivated extension of the standard model, and has important consequences for Higgs phenomenology. Here we consider a scenario where the fourth generation neutrinos are long lived and have both a Dirac and Majorana mass term. Such neutrinos can be as light as 40 GeV and can be the dominant decay mode of the Higgs boson for Higgs masses below the W-boson threshold. We study the effect of the Majorana mass term on the Higgs branching fractions and reevaluate the Tevatron constraints on the Higgs mass. We discuss the prospects for the LHC to detect the semi-invisible Higgs decays into fourth generation neutrino pairs. Under the assumption that the lightest fourth generation neutrino is stable, it's thermal relic density can be up to 20% of the observed dark matter density in the universe. This is in agreement with current constraints on the spin dependent neutrino-neutron cross section, but can be probed by the next generation of dark matter direct detection experiments.

Heavy-neutrino decays at neutrino telescopes

It has been recently proposed that a sterile neutrino \nu_h of mass m_h=40--80 MeV, mixing |U_{\mu h}|^2=10^{-3}--10^{-2}, lifetime \tau_h \lsim 10^{-9} s, and a dominant decay mode (\nu_h \to \nu_\mu \gamma) could be the origin of the experimental anomalies observed at LSND, KARMEN and MiniBooNE. Such a particle would be abundant inside air showers, as it can be produced in kaon decays (K -> \nu_h \mu, K_L -> \nu_h \pi \mu). We use the Z-moment method to evaluate its atmospheric flux and the frequency of its decays inside neutrino telescopes. We show that the \nu_h would imply around 10^4 contained showers per year inside a 0.03 km^3 telescope like ANTARES or the DeepCore in IceCube. These events would have a characteristic energy and zenith-angle distribution (E_\nu = 0.1--10 TeV and \theta < 90^o), which results from a balance between the reach of the heavy neutrino (that disfavors low energies) and a sizeable production rate and decay probability. The standard background from contained neutrino events (\nu_e N \to e X and neutral-current interactions of high inelasticity) is 100 times smaller. Therefore, although it may be challenging from an experimental point of view, a search at ANTARES and IceCube could confirm this heavy-neutrino possibility.

Strong decay patterns of the1−+exotic hybrid mesons

We calculate the coupling constants of the decay modes $1^{-+}\rightarrow\rho\pi, f_1\pi, b_1\pi, \eta\pi, \eta'\pi, a_1\pi, f_1\eta$ within the framework of the light-cone QCD sum rule. Then we calculate the partial width of these decay channels, which differ greatly from the existing calculations using phenomenological models. For the isovector $1^{-+}$ state, the dominant decay modes are $\rho\pi, f_1\pi$. For its isoscalar partner, its dominant decay mode is $a_1\pi$. We also discuss the possible search of the $1^{-+}$ state at BESIII, for example through the decay chains $J/\psi (\psi')\to \pi_1 +\gamma$ or $J/\psi (\psi')\to \pi_1 +\rho$ where $\pi_1$ can be reconstructed through the decay modes $\pi_1\to \rho\pi\to \pi^+\pi^-\pi^0$ or $\pi_1\to f_1(1285)\pi^0$. Hopefully the present work will be helpful to the experimental establishment of the $1^{-+}$ hybrid meson.

Searching for third-generation composite leptoquarks at the LHC

Fermion masses may arise via mixing of elementary fermions with composite fermions of a strong sector in scenarios of strongly-coupled electroweak symmetry breaking. The strong sector may contain leptoquark states with masses as light as several hundred GeV. In the present study we focus on the scalar modes of such leptoquarks since their bosonic couplings are determined completely and hence their production cross sections only depend on their masses. We study all the possible gauge-invariant non-derivative and single-derivative couplings of the scalar leptoquarks to the quarks and leptons, which turn out to be, predominantly, of the third generation. We examine their phenomenology and outline search strategies for their dominant decay modes at the LHC.

Light Higgs boson decaying to four charm quarks

We present a simple supersymmetric model where the dominant decay mode of the lightest Higgs boson is h->2eta->4c where eta is a light pseudoscalar and c is the charm quark. For such decays the Higgs mass can be smaller than 100 GeV without conflict with experiment. Together with the fact that both the Higgs and the pseudoscalar eta are pseudo-Goldstone bosons, this resolves the little hierarchy problem.

Experimental and theoretical indications for an intermediate σ-dressed dibaryon in the NN interaction

Numerous theoretical and experimental arguments in favor of the generation of intermediate σ-dressed dibaryon in NN interaction at middle and short distances are presented. We argue that this intermediate dibaryon should be responsible for the strong middle-range attraction and the short-range repulsion in the NN interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the σ-dressing of the dibaryon is identical to that which explains the Roper-resonance structure, its dominant decay mode and its extraordinary low mass. It is arguing that the (partial) chiral symmetry restoration effects, common for the Roper resonance and dressed dibaryon, are responsible for strong renormalizing of their masses and widths and the observed σ-meson mass and decay width as well. The new experimental data on 2 π-production in the scalar–isoscalar channel produced in pn- and pd-collisions and recent data on γγ correlations in pC and dC scattering in the GeV region seems to corroborate the existence of the σ-dressed dibaryon in two- and three-nucleon interactions. A similar transformation mechanism from the glue to the scalar field can be valid also in some J/ Ψ decays and in enormous σ-meson production in central pp collisions at high energies.

Three-body structure of low-lying 18Ne states

We investigate to what extent 18Ne can be descibed as a three-body system made of an inert 16O-core and two protons. We compare to experimental data and occasionally to shell model results. We obtain three-body wave functions with the hyperspherical adiabatic expansion method. We study the spectrum of 18Ne, the structure of the different states and the predominant transition strengths. Two 0+, two 2+, and one 4+ bound states are found where they are all known experimentally. Also one 3+ close to threshold is found and several negative parity states, 1-, 3-, 0-, 2-, most of them bound with respect to the 16O excited 3- state. The structures are extracted as partial wave components, as spatial sizes of matter and charge, and as probability distributions. Electromagnetic decay rates are calculated for these states. The dominating decay mode for the bound states is E2 and occasionally also M1.

Gluinonia: Energy levels, production and decay

Predictions for energy levels, production and decay rate of gluinonia, non-relativistic bound states of gluinos, are presented. The potential between color-octet constituents is derived in next-to-next-to-leading order and one-loop QCD corrections are derived for the production cross section and the decay rate into gluon jets. In addition we evaluate the decay rate into top quarks and into two photons. The signal-to-background ratio is estimated for the dominant decay mode and found to be around 0.5%. For relatively light gluinos the bound states thus might be detectable.

Dibaryon concept for nuclear force and its experimental evidence

Numerous theoretical and experimental arguments are presented in favor of the generation of intermediate σ-dressed dibaryon in NN interaction at middle and short distances. We argue that this intermediate dibaryon can be responsible for the strong middle-range attraction and the short-distance repulsion in the NN interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the σ dressing of the dibaryon is identical to that which explains the Roper-resonance structure, its dominant decay modes, and its extraordinary low mass. A similar transformation mechanism from the glue to the scalar field was discovered in J/ψ decays. The new experimental data on 2π production in the scalar-isoscalar channel in pn and pd collisions and in, particular, the very recent data on γγ correlations in pC and dC scattering in the GeV region seems to corroborate the existence of the σ-dressed dibaryon in two- and three-nucleon interactions.

Higgs-pair production and decay in simplest little Higgs model

In the framework of the simplest little Higgs model (SLHM), we study the production of a pair of neutral CP-even Higgs bosons at the LHC. First, we examine the production rate and find that it can be significantly larger than the SM prediction. Then we investigate the decays of the Higgs-pair and find that for a low Higgs mass their dominant decay mode is h h → η η η η ( η is a CP-odd scalar) while h h → b b ¯ η η and h h → η η W W may also have sizable ratios. Finally, we comparatively study the rates of p p → h h → b b ¯ τ + τ − , p p → h h → b b ¯ γ γ , and p p → h h → W W W W in the SLHM and the littlest Higgs models (LHT). We find that for a light Higgs, compared with the SM predictions, all the three rates can be sizably enhanced in the LHT but severely suppressed in the SLHM; while for an intermediately heavy Higgs, both the LHT and SLHM can enhance sizably the SM predictions.

The systematic study of spontaneous fission versus alpha decay of superheavy nuclei

The competition between the alpha decay and spontaneous fission half-lives of even–even elements with Z = 100–122 is studied using the Coulomb and proximity potential model and the phenomenological formula for spontaneous fission. The isotopes situated within the spontaneous fission half-life parabola will have alpha decay as the dominant mode of decay. We have studied the Seaborg plots connecting the spontaneous fission half-lives with the fissionability parameter (Z2/A) in the superheavy region for isotopes with Z = 100–138. The role of relative neutron excess in spontaneous fission half-lives is also studied. The isotopes in the first quadrant of the plot for the ratio of spontaneous fission to alpha decay half-lives against relative neutron excess will survive fission and can be synthesized and detected through alpha decay. Our computed alpha decay half-lives for all isotopes agree with the values calculated by the Viola–Seaborg empirical formula and with the experimental data.

Upper limits on the Peccei–Quinn scale and on the reheating temperature in axino dark matter scenarios

Considering axino cold dark matter scenarios with a long-lived charged slepton, we study constraints on the Peccei–Quinn scale fa and on the reheating temperature TR imposed by the dark matter density and by big bang nucleosynthesis (BBN). For an axino mass compatible with large-scale structure, ma˜≳100 keV, temperatures above 109 GeV become viable for fa>3×1012 GeV. We calculate the slepton lifetime in hadronic axion models. With the dominant decay mode being two-loop suppressed, this lifetime can be sufficiently large to allow for primordial bound states leading to catalyzed BBN of lithium-6 and beryllium-9. This implies new upper limits on fa and on TR that depend on quantities which will be probed at the Large Hadron Collider.

Gravitino dark matter and the flavour structure of R-violating operators

We study gravitino dark matter and slow gravitino decays within the framework of R-violating supersymmetry, with particular emphasis on the flavour dependence of the branching ratios and the allowed R-violating couplings. The dominant decay modes and final state products turn out to be very sensitive to the R-violating hierarchies. Mixing effects can be crucial in correctly deriving the relative magnitude of the various contributions, particularly for heavy flavours with phase space suppression. The study of the strength of different decay rates for the gravitino is also correlated to collider signatures expected from decays of the Next-to-Lightest Supersymmetric Particle (NLSP) and to single superparticle production.

Measurement of the [formula omitted] branching fraction and a search for second-class currents in [formula omitted

The τ − → η π − π + π − ν τ decay with the η → γ γ mode is studied using 384 fb−1 of data collected by the BaBar detector. The branching fraction is measured to be ( 1.60 ± 0.05 ± 0.11 ) × 10 − 4 . It is found that τ − → f 1 ( 1285 ) π − ν τ → η π − π + π − ν τ is the dominant decay mode with a branching fraction of ( 1.11 ± 0.06 ± 0.05 ) × 10 − 4 . The first error is statistical and the second systematic. In addition, a 90% confidence level upper limit on the branching fraction of the τ − → η ′ ( 958 ) π − ν τ decay is measured to be 7.2 × 10 − 6 . This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.

Theoretical study on Ne 1s photoionization and corresponding Auger decay processes

In this paper, the Ne 1s photoelectron spectrum and the corresponding Auger decay processes have been investigated theoretically by using the GRASP92, RATIP and the recently developed RERR06 codes based on the multi-configuration Dirac-Fock method. Good overall agreement was found between the present calculations and the previous theoretical and experimental results. By analyzing the Auger decay processes of the photoionization satellite state Ne+1s-12p-1（1,3Ｐ）3p, it was found that the spectator Auger decay is the dominant decay mode and the Auger intensity of the Ne+1s-12p-1（1Ｐ）3p is greater than that of the Ne+1s-12p-1（3Ｐ）3p as a whole. Meanwhile, the relative populations of the final ions Ne+, Ne2+and Ne3+produced by the photoionization satellite state Ne+1s-12p-1（1,3Ｐ）3p were predicted to be 0.02, 0.58 and 0.41, respectively.

A minimal little Higgs model

We discuss a little Higgs scenario that introduces below the TeV scale just the two minimal ingredients of these models, a vectorlike $T$ quark and a singlet component (implying anomalous couplings) in the Higgs field, together with a pseudoscalar singlet $\ensuremath{\eta}$. In the model, which is a variation of Schmaltz's simplest little Higgs model, all the extra vector bosons are much heavier than the $T$ quark. In the Yukawa sector the global symmetry is approximate, implying a single large coupling per flavor, whereas in the scalar sector it is only broken at the loop level. We obtain the one-loop effective potential and show that it provides acceptable masses for the Higgs $h$ and for the singlet $\ensuremath{\eta}$ with no need for an extra $\ensuremath{\mu}$ term. We find that ${m}_{\ensuremath{\eta}}$ can be larger than ${m}_{h}/2$, which would forbid the (otherwise dominant) decay mode $h\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\eta}$.

Alpha decay, cluster decay and spontaneous fission in 294–326122 isotopes

The cluster decay half lives for 294–326122 isotopes are computed for various clusters ranging from an alpha particle to 70Ni within the Coulomb and proximity potential model. The computed alpha decay half lives agree with the values calculated using the Viola–Seaborg–Sobiczewski (VSS) systematic formulas. The half lives for spontaneous fission of these isotopes are carried out using the formula of Ren et al. It is found that the alpha emission is the dominant mode of decay for isotopes with mass number A < 306, and for those with A > 306 spontaneous fission is found to be dominant. The demarcation between alpha decay and spontaneous fission is at 306122, which shows the presence of a spherical neutron shell closure at N = 184.

Measurement of theτ−→ηπ−π+π−ντbranching fraction and a search for a second-class current in theτ−→η′(958)π−ντdecay

The "\tau\to 3\pi\eta\nu" decay with the "\eta \to \gamma\gamma" mode is studied using 384 fb^-1 of data collected by the BaBar detector. The branching fraction is measured to be (1.60+/-0.05+/-0.11)x10^-4. It is found that "\tau \to f1 \pi \nu to 3\pi \eta \nu" is the dominant decay mode with a branching fraction of (1.11+/-0.06+/-0.05)x10^-4. The first error on the branching fractions is statistical and the second systematic. In addition, a 90% confidence level upper limit on the branching fraction of the "\tau \to \eta'(958) \pi \nu" decay is measured to be 7.2x10^-6. This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.