Partial Decay Widths Research Articles

Loop effects on the Higgs decay widths in extended Higgs models

In order to identify the Higgs sector using future precision data, we calculate the partial decay widths of the discovered Higgs boson with the mass of 125 GeV into fermion pairs and gauge-boson pairs with one-loop electroweak and one-loop QCD corrections in various extended Higgs models, such as the Higgs singlet model and four types of two Higgs doublet models. In the tree-level analysis, the patterns of deviations from the standard model predictions in the partial decay widths for various decay modes are distinctive for each model, due to the mixing of the Higgs boson with other neutral scalars. Our present analysis shows that even with a full set of radiative corrections we can discriminate these extended Higgs models via the partial decay widths as long as any of the deviations is detected at future precision measurements. Furthermore, we quantitatively show that in each model the magnitude of the deviations can provide important information on the mass scale of extra Higgs bosons under the theoretical constraints from perturbative unitary and vacuum stability, which can be obtained without discovery of the additional Higgs bosons.

Triangle mechanism in τ → f1(1285)πντ decay

We show that the τ− decay into f1(1285)π−ντ is dominated by a triangle loop mechanism with K⁎, K¯⁎ and K (or K¯) as internal lines, which manifests a strong enhancement reminiscent of a nearby singularity present in the narrow K⁎ limit and the near K¯⁎K⁎ threshold of the internal K⁎ propagators. The f1(1285) is then produced by its coupling to the K⁎K¯ and K¯⁎K which is obtained from a previous model where this resonance was dynamically generated as a molecular K⁎K¯ (or K¯⁎K) state using the techniques of the chiral unitary approach. We make predictions for the f1π mass distribution which significantly deviates from the phase-space shape, due to the distortion caused by the triangle mechanism and the K⁎K¯ threshold. We find a good agreement with the experimental value within uncertainties for the integrated partial decay width, which is a clear indication of the importance of the triangle mechanism in this decay and supports the dynamical origin of the f1(1285) as a K⁎K¯ and K¯⁎K molecular state.

Strong and radiative decays of DΞ molecular state and newly observed Ωc states

In this work, we study strong and radiative decays of S-wave D\Xi molecular state, which is related to the \Omega^*_c states newly observed at LHCb. The coupling between the D\Xi molecular state and its constituents D and \Xi is calculated by using the compositeness condition. With the obtained coupling, the partial decay widths of the D\Xi molecular state into the \Xi_c^{+}K^{-}, \Xi^{'+}_cK^{-} and \Omega^{*}_c(2695)\gamma final states through hadronic loop are calculated with the help of the effective Lagrangians. By comparison with the LHCb observation, the current results of total decay width support the \Omega^{*}_c(3119) or \Omega^{*}_c(3050) as D\Xi molecule while the the decay width of the \Omega^{*}_c(3000), \Omega^{*}_c(3066) and \Omega^{*}_c(3090) can not be well reproduced in the molecular state picture. The partial decay widths are also presented and helpful to further understand the internal structures of \Omega^{*}_c(3119) and \Omega^{*}_c(3050).

Study of KS0 pair production in single-tag two-photon collisions

We report a measurement of the cross section for $K^0_S$ pair production in single-tag two-photon collisions, $\gamma^* \gamma \to K^0_S K^0_S$, for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon. The measurement covers the kinematic range 1.0 GeV < W < 2.6 GeV and $|\cos \theta^*| < 1.0$ for the total energy and kaon scattering angle, respectively, in the $\gamma^* \gamma$ center-of-mass system. These results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For the first time, the transition form factor of the $f_2'(1525)$ meson is measured separately for the helicity-0, -1, and -2 components and also compared with theoretical calculations. Finally, the partial decay widths of the $\chi_{c0}$ and $\chi_{c2}$ mesons are measured as a function of $Q^2$.

Precision calculations for h \u2192 WW/ZZ \u2192 4 fermions in the Two-Higgs-Doublet Model with Prophecy4f

We have calculated the next-to-leading-order electroweak and QCD corrections to the decay processes h → WW/ZZ → 4 fermions of the light CP-even Higgs boson h of various types of Two-Higgs-Doublet Models (Types I and II, “lepton-specific” and “flipped” models). The input parameters are defined in four different renormalization schemes, where parameters that are not directly accessible by experiments are defined in the overline{mathrm{MS}} scheme. Numerical results are presented for the corrections to partial decay widths for various benchmark scenarios previously motivated in the literature, where we investigate the dependence on the overline{mathrm{MS}} renormalization scale and on the choice of the renormalization scheme in detail. We find that it is crucial to be precise with these issues in parameter analyses, since parameter conversions between different schemes can involve sizeable or large corrections, especially in scenarios that are close to experimental exclusion limits or theoretical bounds. It even turns out that some renormalization schemes are not applicable in specific regions of parameter space. Our investigation of differential distributions shows that corrections beyond the Standard Model are mostly constant offsets induced by the mixing between the light and heavy CP-even Higgs bosons, so that differential analyses of h→4f decay observables do not help to identify Two-Higgs-Doublet Models. Moreover, the decay widths do not significantly depend on the specific type of those models. The calculations are implemented in the public Monte Carlo generator Prophecy4f and ready for application.

The neutral Higgs self-couplings in the (h)MSSM

We consider the Minimal Supersymmetric extension of the Standard Model in the regime where the supersymmetric breaking scale is extremely large. In this MSSM, not only the Higgs masses will be affected by large radiative corrections, the dominant part of which is provided by the third generation quark/squark sector, but also the various self-couplings among the Higgs states. In this note, assuming that squarks are extremely heavy, we evaluate the next-to-leading order radiative corrections to the two neutral CP-even Higgs self-couplings λHhh and λhhh and to the partial decay width Γ(H→hh) that are most relevant at the LHC. The calculation is performed using an effective field theory approach that resums the large logarithmic squark contributions and allows to keep under control the perturbative expansion. Since the direct loop vertex corrections are generally missing in this effective approach, we have properly renormalised the effective theory to take them into account. Finally, we perform a comparison of the results in this effective MSSM with those obtained in a much simpler way in the so-called hMSSM approach in which the mass value for the lightest Higgs boson Mh=125 GeV is used as an input. We show that the hMSSM provides a reasonably good approximation of the corrected self-couplings and H→hh decay rate and, hence, it can be used also in these cases.

First measurement of S30+α resonant elastic scattering for the S30(α,p) reaction rate

Background: Type I x-ray bursts are the most frequent thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The $^{30}$S($\alpha$,p) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in $^{34}$Ar and determine their quantum properties. In particular, natural-parity states with large $\alpha$-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of $^{30}$S+$\alpha$ resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for $^{30}$S($\alpha$,$\alpha$) near $150^{\circ}$ in the center-of-mass frame. The experimental data were analyzed with an $R$-Matrix calculation, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of $^{30}$S($\alpha$,p) based on all available experimental data of $^{34}$Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the $^{30}$S($\alpha$,p)$^{33}$Cl rate significantly affects the predicted nuclear energy generation rate during the burst.

Higgs decay into four charged leptons in the presence of dimension-six operators

We study the indirect effects of New Physics in the Higgs decay into four charged leptons, using an Effective Field Theory (EFT) approach to Higgs interactions. We evaluate the deviations induced by the EFT dimension-six operators in observables like partial decay width and various kinematic distributions, including angular observables, and compare them with the contribution of the full SM electroweak corrections. The calculation is implemented in an improved version of the event generator Hto4l, which can provide predictions in terms of different EFT-bases and is available for data analysis at the LHC. We also perform a phenomenological study in order to assess the benefits coming from the inclusion of differential information in the future analyses of very precise data which will be collected during the high luminosity phase of the LHC.

D∗(2380) Resonance in a Chiral SU(3) Constituent Quark Model

Recent studies on the newly observed resonance [Formula: see text] with a compact structure in a chiral SU(3) constituent quark model are briefly reported. the overall properties, including the mass, the partial decay widths in various decay modes, and the total width, comparing with the experimental data, show that a compact hexaquark dominated structure might be a reasonable interpretation for this state. Moreover, the charge distribution of [Formula: see text] is also discussed.

Compact pentaquark states

We investigated the lightest pentaquark state observed by the LHCb collaboration as a compact five-quark ground-state, with spin S = 3/2, and we showed that this state belongs to a SUf(3) flavor octet by means of a group theory approach. Moreover, we predicted in a parameter-free way the pentaquark state mass spectra for all the octet-pentaquark states. Finally, by means of an effective Lagrangian approach, we computed the octet-pentaquark partial decay widths in J/ψΛ, J/ψΣ and J/ψΞ channels.

The Mass and Decay Properties of the 1−+ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the (1−+,0++) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of 〈g3G3〉 increase the QCD sum rule mass prediction for the 1−+ light hybrid. The obtained conservative mass range 1.72–2.60 GeV does not favor the π1(1400) and the π1(1600) to be pure hybrid states and suggests the π1(2015) observed by E852 is more likely to have much of a hybrid constituent. We also study the b1π and ρπ decay patterns of the 1−+ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the b1π mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the ρπ mode is very small due to the lack of the leading twist contribution in the light-cone expansion of the correlation function.

Pentaquarks with hidden charm as hadroquarkonia

We consider hidden charm pentaquarks as hadroquarkonium states in a QCD inspired approach. Pentaquarks arise naturally as bound states of quarkonia excitations and ordinary baryons. The LHCb P_c(4450) pentaquark is interpreted as a psi '-nucleon bound state with spin-parity J^P=3/2^-. The partial decay width varGamma (P_c(4450)rightarrow J/psi +N)approx 11 MeV is calculated and turned out to be in agreement with the experimental data for P_c(4450). The P_c(4450) pentaquark is predicted to be a member of one of the two almost degenerate hidden-charm baryon octets with spin-parities J^{P}=1/2^-,3/2^-. The masses and decay widths of the octet pentaquarks are calculated. The widths are small and comparable with the width of the P_c(4450) pentaquark, and the masses of the octet pentaquarks satisfy the Gell-Mann–Okubo relation. Interpretation of pentaquarks as loosely bound varSigma _cbar{D}^* and varSigma _c^*bar{D}^* deuteronlike states is also considered. We determine quantum numbers of these bound states and calculate their masses in the one-pion exchange scenario. The hadroquarkonium and molecular approaches to exotic hadrons are compared and the relative advantages and drawbacks of each approach are discussed.

A systematic study of mass spectra and strong decay of strange mesons

The mass spectrum of the kaon family is analyzed by the modified Godfrey–Isgur model with a color screening effect approximating the kaon as a heavy–light meson system. This analysis gives us the structure and possible assignments of the observed kaon candidates, which can be tested by comparing the theoretical results of their two-body strong decays with the experimental data. Additionally, prediction of some partial decay widths is made on the kaons still missing in experiment. This study is crucial to establishing the kaon family and searching for their higher excitations in the future.

Generic calculation of two-body partial decay widths at the full one-loop level

We describe a fully generic implementation of two-body partial decay widths at the full one-loop level in the SARAH and SPheno framework compatible with most supported models. It incorporates fermionic decays to a fermion and a scalar or a gauge boson as well as scalar decays into two fermions, two gauge bosons, two scalars or a scalar and a gauge boson. We present the relevant generic expressions for virtual and real corrections. Whereas wave-function corrections are determined from on-shell conditions, the parameters of the underlying model are by default renormalised in a overline{text {DR}} (or overline{text {MS}}) scheme. However, the user can also define model-specific counter-terms. As an example we discuss the renormalisation of the electric charge in the Thomson limit for top-quark decays in the standard model. One-loop-induced decays are also supported. The framework additionally allows the addition of mass and mixing corrections induced at higher orders for the involved external states. We explain our procedure to cancel infrared divergences for such cases, which is achieved through an infrared counter-term taking into account corrected Goldstone boson vertices. We compare our results for sfermion, gluino and Higgs decays in the minimal supersymmetric standard model (MSSM) against the public codes SFOLD, FVSFOLD and HFOLD and explain observed differences. Radiatively induced gluino and neutralino decays are compared against the original implementation in SPheno in the MSSM. We exactly reproduce the results of the code CNNDecays for decays of neutralinos and charginos in R-parity violating models. The new version SARAH 4.11.0 by default includes the calculation of two-body decay widths at the full one-loop level. Current limitations for certain model classes are described.

Selected strong decays of η(2225) and ϕ(2170) as ΛΛ¯ bound states

The strong decays of the two resonances $\eta(2225)$ and $\phi(2170)$ are discussed for selected decay channels. The two resonances are considered as the $\Lambda \bar{\Lambda}$ bound states in the molecular scenario. The phenomenological hadronic molecular approach is employed for the calculation of respective decay modes using effective Lagrangians. Our results show that the decay modes $\eta(2225)\to K^*K$ and $\phi(2175) \to KK$ dominate over the partial decay widths of $\eta(2275)\to VV (\phi\phi, \omega\omega, K^*K^*)$ and $\phi(2175)\to VS (\omega\sigma, K^*K^*_0(800), \phi f_0(980))$ due to phase space and couplings.

Evidence for O15+α resonance structures in Ne19 via direct measurement

States in the astrophysically important Ne19 nucleus have been populated directly using the O15(α,α)O15 reaction with a radioactive O15 beam. Due to the challenges involved, this represents the first such O15 measurement with high resolution and the first dedicated to exploring the cluster structure. This measurement comprises three experiments: the first to develop the O15 radioactive beam, the second the resonant scattering study, and the third to measure the precise energy loss of O ions in He4 to reduce systematic uncertainties. The results show evidence for O15+α cluster structure which could explain earlier results pointing to the increased α branching ratio in the astrophysical reaction rate for high-spin near-threshold resonances. Absolute differential cross sections have been measured. Additionally, spins, parities, and partial decay widths, essential for nuclear reaction-rate calculations, have been extracted using an R-matrix analysis.Received 25 July 2016Revised 3 August 2017DOI:https://doi.org/10.1103/PhysRevC.96.044317©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayCluster modelsDirect reactionsH & He induced nuclear reactionsNuclear spin & parityNuclear structure & decaysUnstable nuclei induced nuclear reactionsProperties6 ≤ A ≤ 19Nuclear Physics

Jost function method approach for study of unstable nuclei

We have developed the formalism of the Jost function method (JFM) to study unstable nuclei. We apply the JFM to the calculations, the partial decay widths in the coupled-channel problem, anti-bound (virtual) states, non-local potentials and Lagrange-mesh method. The results are compared with other methods, and we show the JFM formalism is useful to study the unstable nuclei.

Partial widths of a multi-channel resonance

A new method for finding the partial decay-widths for multi-channel resonances is suggested. It is based on using the Jost matrices. These matrices can be either calculated (when the multi-channel potential is known) or found by fitting experimental data (when they are available). In both cases the procedure for obtaining the partial widths is the same and is simple. It does not require any kind of integration or differentiation. The partial widths sum up to the total width and the corresponding branching ratios can be found as some algebraic combinations of the elements of the Jost matrices.

Triangle mechanisms in the build up and decay of the N*(1875)

We have studied the $N^*(1875) (3/2^-)$ resonance with a multichannel unitary scheme, considering the $\Delta \pi$ and $\Sigma^* K$, with their interaction extracted from chiral Lagrangians, and then have added two more channels, the $N^*(1535) \pi$ and $N \sigma$, which proceed via triangle diagrams involving the $\Sigma^* K$ and $\Delta \pi$ respectively in the intermediate states. The triangle diagram in the $N^*(1535) \pi$ case develops a singularity at the same energy as the resonance mass. We determine the couplings of the resonance to the different channels and the partial decay widths. We find a very large decay width to $\Sigma^* K$, and also see that, due to interference with other terms, the $N \sigma$ channel has an important role in the $\pi \pi$ mass distributions at low invariant masses, leading to an apparently large $N \sigma$ decay width. A discussion is done, justifying the convenience of an experimental reanalysis of this resonance to the light of the findings of the paper, using multichannel unitary schemes.

Phenomenological features of two-proton virtual decay of the 45Fe nucleus

On the basis of the theory of diagonal two-proton two-step virtual decays of spherical nuclei that was developed earlier and the superfluid model of the nucleus, the total and partial widths for the two-proton decay of the 45Fe parent nucleus in the ground state to the ground state of the 43Cr daughter nucleus were calculated along with the angular distribution of protons emitted in this decay. The calculated features of this mode of 45Fe decay were shown to be highly sensitive to the choice of form for nucleon shell potentials. It is also shown that there exists a potential such with which one can construct a successful simultaneous description of the experimental total width and the angular distribution of emitted protons for the aforementioned two-proton mode of decay of the 45Fe nucleus.