Pionic Decay Widths Research Articles

Understandingd*(2380) in a chiral quark model

We review our recent progresses made in the study of the structure and decay properties of the newly observedd*(2380) within a chiral constituent quark model. It is found that thed*(2380) can be explained as a compact hexaquark-dominated exotic state with a fraction of hidden color components of about 2/3 in its configuration. Based on this scenario the single- and double- pionic partial decay widths are calculated and the corresponding numerical results are in good agreement with the experimental data.

On the Decays of d*(2380) in a Constituent Chiral Quark Model

The recent studies of the newly observed dibaryon resonance d*(2380) in a constituent chiral quark model are briefly summarized. An overall analysis of the obtained pionic decay widths, comparing with the experimental data, shows that a compact hexaquark system might be a reasonable interpretation for this dibaryon resonance with I(JP ) = 0(3+).

Lorentz invariance violation as an explanation of the muon excess in Auger data

The Auger Collaboration has observed the number of muons, which is higher than its prediction by existing hadronic interaction models. We explain this excess of muons by using Lorentz invariance violation (LIV) in the photon sector. As an outcome of Lorentz invariance violation, the dispersion relation of the photon gets modified, which we use for the calculation of ${\ensuremath{\pi}}^{0}$ decay width. In the Auger data of primary energy $1{0}^{9.8}<E(\mathrm{GeV})<1{0}^{10.2}$, we find that the neutral pion decay width is suppressed in comparison to its standard model (SM) counterpart. As a result, we get a large number of muons explaining the observed muon excess. We consider Planck-suppressed LIV at order $\mathcal{O}({p}^{2}/{M}_{\mathrm{Pl}}^{2})$ for studying the photon sector, which is in agreement with the current bounds and not as tightly constrained as LIV at order $\mathcal{O}(p/{M}_{\mathrm{Pl}})$.

Baryon Masses and Hadronic Decay Widths with Explicit Pionic Contributions

We report results from studies of baryon ground and resonant states by taking explicit mesonic degrees of freedom into account. We are following a relativistic coupled-channels approach relying on a Poincaré-invariant mass operator in matrix form. Generally, it corresponds to a bare particle that is coupled to a number of further mesonic channels. Here we present results, where the bare particle is either a bare nucleon or a bare Delta coupled to pion–nucleon and pion–Delta channels, respectively. For the pion–baryon vertices we employ coupling constants and form factors from different models in the literature. From the mass-operator eigenvalue equation we obtain the pion-dressing effects on the nucleon mass as well as the mass and pion-decay width of the Delta. The dressed masses become smaller than the bare ones, and a finite width of the Delta is naturally generated. The results are relevant for the construction of constituent-quark models for baryons, which have so far not included explicit mesonic degrees of freedom, but have rather relied on three-quark configurations only.

Pion production via proton synchrotron radiation in strong magnetic fields in relativistic field theory: Scaling relations and angular distributions

We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are $n_{i,f} \sim 10^4 - 10^5$. We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of $10^{15}$G, where $n_{i,f} \sim 10^{12} - 10^{13}$, from the results for $n_{i,f} \sim 10^4 - 10^5$. The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed.

Two-Photon Decay of the Neutral Pion in Lattice QCD

We perform a nonperturbative calculation of the π(0) → γγ transition form factor and the associated decay width using lattice QCD. The amplitude for a two-photon final state, which is not an eigenstate of QCD, is extracted through a Euclidean time integral of the relevant three-point function. We utilize the all-to-all quark propagator technique to carry out this integration as well as to include the disconnected quark diagram contributions. The overlap fermion formulation is employed on the lattice to ensure exact chiral symmetry on the lattice. After examining various sources of systematic effects, except for a possible discretization effect, we obtain Γπ(0) → γγ = 7.83(31)(49) eV for the pion decay width, where the first error is statistical and the second is our estimate of the systematic error.

Bs1(5830)andBs2*(5840)

In this paper we investigate the strong decays of the two newly observed bottom-strange mesons ${B}_{s1}(5830)$ and ${B}_{s2}^{*}(5840)$ in the framework of the quark pair creation model. The two-body strong decay widths of ${B}_{s1}(5830{)}^{0}\ensuremath{\rightarrow}{B}^{*+}{K}^{\ensuremath{-}}$ and ${B}_{s2}^{*}(5840{)}^{0}\ensuremath{\rightarrow}{B}^{+}{K}^{\ensuremath{-}}$, ${B}^{*+}{K}^{\ensuremath{-}}$ are calculated by considering ${B}_{s1}(5830)$ to be a mixture between $|^{1}P_{1}⟩$ and $|^{3}P_{1}⟩$ states, and ${B}_{s2}^{*}(5840)$ to be a $|^{3}P_{2}⟩$ state. The double pion decay of ${B}_{s1}(5830)$ and ${B}_{s2}^{*}(5840)$ is supposed to occur via the intermediate state $\ensuremath{\sigma}$ and ${f}_{0}(980)$. Although the double pion decay widths of ${B}_{s1}(5830)$ and ${B}_{s2}^{*}(5840)$ are smaller than the two-body strong decay widths of ${B}_{s1}(5830)$ and ${B}_{s2}^{*}(5840)$, one suggests future experiments to search the double pion decays of ${B}_{s1}(5830)$ and ${B}_{s2}^{*}(5840)$ due to their sizable decay widths.

Dwave heavy mesons

We first extract the binding energy {lambda} and decay constants of the D wave heavy meson doublets (1{sup -},2{sup -}) and (2{sup -},3{sup -}) with QCD sum rule in the leading order of heavy quark effective theory. Then we study their pionic ({pi},K,{eta}) couplings using the light-cone sum rule, from which the parameter {lambda} can also be extracted. We then calculate the pionic decay widths of the strange/nonstrange D wave heavy D/B mesons and discuss the possible candidates for the D wave charm-strange mesons. Further experimental information, such as the ratio between D{sub s}{eta} and DK modes, will be very useful to distinguish various assignments for D{sub sJ}(2860 2715)

Role ofqq¯components in theN(1440)resonance

The role of 5-quark components in the pion and electromagnetic decays and transition form factors of the N(1440) is explored. The $qqqq\bar q$ components, where the 4-quark subsystem has the flavor-spin symmetries $[4]_{FS}[22]_F[22]_S$ and $[4]_{FS}[31]_F[31]_S$, which are expected to have the lowest energy of all $qqqq\bar q$ configurations, are considered in detail with a nonrelativistic quark model. The matrix elements between the 5-quark components of the N(1440) and the nucleon, $qqqq\bar q\to qqqq\bar q$, play a minor role in these decays, while the transition matrix elements $qqqq\bar q\to qqq$ and $qqq\to qqqq\bar q$ that involve quark antiquark annihilation are very significant. Both for the electromagnetic and strong decay the change from the valence quark model value is dominated by the confinement triggered $q\bar q$ annihilation transitions. In the case of pion decay the calculated decay width is enhanced substantially both by the direct $q\bar q \to \pi$ and also by the confinement triggered $q\bar q\to \pi$ transitions. Agreement with the empirical value for the pion decay width may be reached with a $\sim$ 30% $qqqq\bar q$ component in the N(1440).

Pionic decays ofDsj(2317),Dsj(2460)andBsj(5718),Bsj(5765)

We estimate pionic decay widths of the narrow charm-strange resonances ${D}_{sj}(2317)$ and ${D}_{sj}(2460)$ using the $^{3}P_{0}$ model. Their one-pion decays occur through $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\pi}}^{0}$ mixing while the two-pion decays of ${D}_{sj}(2460)$ occur through the virtual ${f}_{0}(980)$ meson. The mixing between $^{3}P_{0}$ and $^{1}P_{1}$ states enhances the single-pion decay width of ${D}_{sj}(2460)$ and suppresses its double-pion decay width significantly. As a byproduct, we also calculate pionic decay widths of ${B}_{sj}(5765)$, ${B}_{sj}(5765)$ mesons in the $({0}^{+},{1}^{+})$ heavy doublet.

Strong decays ofDsJ(2317)andDsJ(2460)

With the identification of $({D}_{sJ}(2317),{D}_{sJ}(2460))$ as the $({0}^{+},{1}^{+})$ doublet in the heavy quark effective field theory, we derive the light-cone QCD sum rule for the coupling of an eta meson with ${D}_{sJ}(2317){D}_{s}$ and ${D}_{sJ}(2460){D}_{s}^{*}$. Through $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\pi}}^{0}$ mixing we calculate their pionic decay widths, which are consistent with the experimental values (or upper limits). Combining the radiative decay widths derived by Colangelo, Fazio, and Ozpineci in the same framework, we conclude that the decay patterns of ${D}_{sJ}(2317,2460)$ strongly support their interpretation as ordinary $c\overline{s}$ mesons.

THE CHIRAL QUARK MODEL AND BARYON PHENOMENOLOGY

The chiral quark model posits that pions couple to the axial current of constituent quarks. This chiral pion coupling governs the pion decays of baryon resonances and also implies pion and multipion interactions between the quarks. The qualitative features of this model for the description of pionic decay widths and baryon spectra are outlined. When the covariant quark model wave function for the nucleon is chosen so as to describe the empirical nucleon form factors the pion decay widths of the positive parity resonances are underpredicted. This indicates the presence of significant multiquark components in these resonances.

Precise Determination of|Vus|from Lattice Calculations of Pseudoscalar Decay Constants

Combining the ratio of experimental kaon and pion decay widths, Gamma(K-->munu (mu)(gamma))/Gamma(pi-->munu (mu)(gamma)), with a recent lattice gauge theory calculation of f(K)/f(pi) provides a precise value for the Cabibbo-Kobayashi-Maskawa quark mixing matrix element |V(us)|=0.2219(25) or if three generation unitarity is assumed |V(us)|=0.222 1(24). Comparison with other determinations of that fundamental parameter, implications, and an outlook for future improvements are given.

Axial transition form factors and pion decay of baryon resonances

The pion decay constants of the lowest orbitally excited states of the nucleon and the $\Delta(1232)$ along with the corresponding axial transition form factors are calculated with Poincar\'e covariant constituent-quark models with instant, point and front forms of relativistic kinematics. The model wave functions are chosen such that the calculated electromagnetic and axial form factors of the nucleon represent the empirical values in all three forms of kinematics, when calculated with single-constituent currents. The pion decay widths calculated with the three forms of kinematics are smaller than the empirical values. Front and instant form kinematics provide a similar description, with a slight preference for front form, while the point form values are significantly smaller in the case of the lowest positive parity resonances.

Neutral pion decay width in a hot and dense medium

We study the behavior of the $\pi^0$ width as a function of temperature and density. We provide simple expressions for the neutral pion width in a hot and dense medium based on a renormalized version of the microscopic Nambu Jona Lasinio model. Then we consider the two cases where the pion mass is finite or vanishes at the critical temperature and discuss the phenomenological consequences of both cases.

A dressed-bag model study of the short-range NΔ interaction in pion photoproduction processes off the deuteron

The impact of the short-range NΔ interaction on the pion photoproduction processes off the deuteron in the Δ-resonance region is studied in the framework of a recently proposed dressed-bag model. A common dressing procedure for bare three- and six-quark states is used to describe both the pion decay widths of baryon resonances and the effective NN (or NΔ) interaction at short ranges. It is shown that the effect of short-range NΔ interaction for the forward-angle π0 photoproduction off the deuteron cannot be neglected. The prospects for further development of the model to describe the short-range NN (or NΔ) correlations in the lightest nuclei are discussed.

Pionic decay of Λ hypernuclei in a continuum shell model

We evaluate pionic decay widths of \ensuremath{\Lambda} hypernuclei using a shell model for both the nuclear bound and continuum nucleon wave functions in the final state and distorted waves for the outgoing pion. An excellent agreement with the recent KEK measurement of ${\ensuremath{\pi}}^{\ensuremath{-}}$-decay widths of ${}_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ and ${}_{\ensuremath{\Lambda}}^{28}\mathrm{Si}$ is found. In addition, results for ${}_{\ensuremath{\Lambda}}^{56}\mathrm{Fe}$ are consistent with the existing upper bound.

Pion decay widths of [formula omitted] mesons

The pionic decay rates of the excited L=0,1 D mesons are calculated with a Hamiltonian model within the framework of the covariant Blankenbecler–Sugar equation. The interaction between the light quark and charm antiquark is described by a linear scalar confining and a screened one-gluon exchange interaction. The decay widths of the D ∗ mesons obtain a contribution from the exchange current that is associated with the linear scalar confining interaction. If this contribution is taken into account along with the single-quark approximation, the calculated decay rates of the charged D ∗ mesons are readily below the current empirical upper limits if the axial coupling constant of the light constituent quarks is taken to be g A q = 0.87, but reach the empirical upper limits if g A q = 1. With the conventional values for g A q , the calculated widths of the D 1 and D 2 ∗ mesons fall somewhat below the experimental lower limits, leaving room for other decay modes as well, such as ππ decay. The unrealistically large contribution from the axial charge operator to the calculated pion decay width of the D 1 meson is suppressed by taking into account the exchange charge effects that are associated with the scalar linear confining and vector one-gluon exchange interactions. The predicted values for the pionic widths of the hitherto undiscovered L=1 D 1 ∗ and D 0 ∗ mesons are found to be smaller than previous estimates.

Nucleon resonance transition couplings to vector mesons

Recent heavy-ion experiments indicate modifications of the ρ-meson mass in medium. In the CERES experiments, ρ mesons are produced at ∼ normal nuclear matter density, where hadrons are more appropriate constituents than quarks. A collective “nuclear ρ”, in which every nucleon is excited to the N(1520) state, with equal amplitude, enters in this description. At the higher densities reached by future experiments, constituent quarks become the appropriate variables. Here the ρ and ω transition couplings to the nucleon resonances up to 1700 MeV, including the N(1520), are derived by means of the chiral quark model. The relevant coupling constants are expressed in terms of the corresponding vector-coupling constants to nucleons. The quality of the model relations is tested by a calculation of the corresponding pion-resonance coupling constants, which are known from the empirical pion-decay widths.

Double-Λ hypernuclei and the nuclear medium effective ΛΛ interaction

We fit the 1 S 0 ΛΛ interaction in the nuclear medium to the masses of the experimentally known double-Λ hypernuclei: ΛΛ 6He, ΛΛ 10Be and ΛΛ 13B. We derive this effective interaction from OBE Jülich ΛΛ-type potentials and using both Hartree-Fock and variational approaches. We find that the inclusion of ΛΛ correlations in the variational scheme leads to significant differences and a better understanding of the dynamical features of the system. We investigate the sensitivity of the binding energies and the mesonic decay widths of the above double-Λ hypernuclei to the ωΛΛ coupling and the form factor at the σΛΛ vertex. We also use this effective interaction to predict binding energies and pionic decay widths of heavier double-Λ hypernuclei, not discovered yet. Finally, we discard the existence of 1S 0 ΛΛ bound states provided the ΛΛ-Ξ N coupling can be neglected.