Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

We evaluate static properties and semileptonic decays for the ground state of doubly heavy Ξ, Ξ', Ξ ^* and Ω, Ω', Ω ^* baryons. Working in the framework of a nonrelativistic quark model, we solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one-gluon exchange. Our results for static properties (masses, charge radii and magnetic moments) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy Ξ, Ξ'(J = 1/2) and Ω, Ω'(J = 1/2) baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark-diquark approximation. An erratum to this article is available at .     

An experiment for the measurement of the bound- β-decay of the free neutron

The hyperfine-state population of hydrogen after the bound-β-decay of the neutron directly yields the neutrino left-handedness or a possible right-handed admixture and possible small scalar and tensor contributions to the weak force. Using the through-going beam tube of a high-flux reactor, a background free hydrogen rate of ca. 3s^-1 can be obtained. The detection of the neutral hydrogen atoms and the analysis of the hyperfine states is accomplished by Lamb shift source type quenching and subsequent ionization. The constraints on the neutrino helicity and the scalar and tensor coupling constants of the weak interaction can be improved by a factor of ten.     

Semileptonic decays of baryons in a relativistic quark model

We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model is based on the Bethe-Salpeter equation in instantaneous approximation. It generates satisfactory mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates in good agreement with experiment.     

Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model

We study the scaling of the ³S₁-¹S₀ meson mass splitting and the pseudoscalar weak-decay constants with the mass of the meson, as seen in the available experimental data. We use an effective light-front QCD-inspired dynamical model regulated at short distances to describe the valence component of the pseudoscalar mesons. The experimentally known values of the mass splitting, decay constants (from global lattice-QCD averages) and the pion charge form factor up to 4 [GeV/c]² are reasonably described by the model.     

Chiral-invariant phase space model

The masses of the SU(3)×SU(6) hadrons are calculated in the chiral-invariant phase space (CHIPS) model as a sum of the mean energies of the quarks at a constant temperature T _c with the color-magnetic splitting and the color-electric shift. The masses of hadrons are parametrized by four constants: T _c, m_s, E _CE and A _CM. With the same number of parameters the CHIPS model fits the masses of hadrons better than the classic bag model. The small mass of the d-quark ( m _d = 2.7MeV) is used to prove that the isotopic shifts of hadrons can be explained by the mass difference between the d- and u-quarks. The dibaryon mass is estimated in CHIPS to be 200MeV higher than in the bag model. The prediction for the mass of the α^* cluster is about the same in both models. It is close to 4 ^. m _Δ. Received: 12 December 2001 / Accepted: 23 May 2002     

Vector and axial-vector mesons in Quasilocal Quark Models

We consider the SU(2) Quasilocal Quark Model of the NJL-type including vector and axial-vector four-fermion interaction vertices with derivatives. The mass spectrum and a set of model-independent relations for the ground and first-excited states are calculated. The chiral-symmetry restoration sum rules in these channels are imposed for matching to QCD at intermediate energies in order to get a number of constraints on parameters of the SU(2) QQM. Received: 15 January 2003 / Accepted: 10 February 2003 / Published online: 29 April 2003     

The K<Emphasis Type="Italic">π</Emphasis> and <Emphasis Type="Italic">ππ</Emphasis> S-wave amplitude from D-meson decays

The issue of Kπ and ππ S-wave amplitude is addressed using decays of D-mesons. Model-independent measurements of the phases of the π ⁺ π ⁺ and K ^- π ⁺ S-wave amplitude from D ⁺→π ^- π ⁺ π ⁺ and D ⁺→K ^- π ⁺ π ⁺ decays are discussed. The result indicates a deviation from the phase of the K ^- π ⁺ S-wave amplitude obtained by scattering experiments. This could be interpreted as an indication of the presence of 3-body final-state interaction, or in other words, that the phases from production and scattering process cannot be directly compared.     

Quark models<Superscript>⋆</Superscript>

The scope of a relativistically covariant constituent quark model of baryons based on the Bethe-Salpeter equation in instantaneous approximation is illustrated by a discussion of various baryon resonance observables such as static electromagnetic moments --including a novel calculational procedure-- form factors and helicity amplitudes, semileptonic decays as well as the systematics of two-body strong decay widths.     

Radial excitations of heavy-light mesons

The recent discovery of D_s states suggests the existence of radial excitations. Our semirelativistic quark potential model succeeds in reproducing these states within one to two percent of accuracy compared with the experiments, D _s0(2860) and D _s ^*(2715), which are identified as 0⁺ and 1^- radial excitations (n = 2). We also present calculations of radial excitations for B/B _s heavy mesons. The relation between our formulation and the modified Goldberger-Treiman relation is also described.     

QCD Coulomb gauge approach to exotic hadrons

The Coulomb gauge Hamiltonian model is used to calculate masses for selected J^PC states consisting of exotic combinations of quarks and gluons: ggg glueballs (oddballs), qˉg hybrid mesons and qˉqˉ tetraquark systems. An odderon Regge trajectory is computed for the J^- glueballs with intercept much smaller than the pomeron, explaining its nonobservation. The lowest 1^-+ hybrid-meson mass is found to be just above 2.2GeV while the lightest tetraquark state mass with these exotic quantum numbers is predicted around 1.4GeV consistent with the observed π(1400).     

Towards an understanding of heavy baryon spectroscopy

The recent observation at CDF and D0 of Σ _b , Σ _b ^* and Ξ _b baryons opens the door to the advent of new states in the bottom baryon sector. The states measured provide sufficient constraints to fix the parameters of phenomenological models. One may therefore consistently predict the full bottom baryon spectra. For this purpose we have solved exactly the three-quark problem by means of the Faddeev method in momentum space. We consider our guidance may help experimentalists in the search for new bottom baryons and their findings will help in constraining further the phenomenological models. We identify particular states whose masses may allow to discriminate between the dynamics for the light quark pairs predicted by different phenomenological models. Within the same framework we also present results for charmed, doubly charmed, and doubly bottom baryons. Our results provide a restricted possible assignment of quantum numbers to recently reported charmed-baryon states. Some of them are perfectly described by D-wave excitations with J ^P = 5/2⁺, as the Λ _c (2880), Λ _c (3055), and Λ _c (3123). Communicated by V. Vento     

A quark model study of semileptonic baryon decays in the electronic decay modes

A relativistic quark model based on Dirac equation with the independent-quark confining potential of the form (1 +γ ⁰)[a ln(r/b)] is used to compute the weak electric and magnetic form factors for semileptonic baryonic decays in the electronic decay modes. The values obtained for (g ₂/g ₁) agree with the non relativistic results and those for (f ₂/f ₁) agree with the MIT bag model values of Donoghue and Holstein. The SU(3) symmetry breaking does not generate appreciable departures in (f ₂/f ₁) values from corresponding Cabibbo values.     

Regarding the axial-vector mesons

The implications of the f₁(1285)-f₁(1420) mixing for the K₁(³P₁)- K₁(¹P₁) mixing angle are investigated. Based on the f₁(1285)-f₁(1420) mixing angle ∼ 50^° suggested from the analysis for a substantial body of data concerning the f₁(1420) and f₁(1285), the masses of the K₁(³P₁) and K₁(¹P₁) are determined to be ∼ 1307.35±0.63 MeV and 1370.03±9.69 MeV, respectively, which therefore suggests that the K₁(³P₁)- K₁(¹P₁) mixing angle is about ±(59.55±2.81)^°. Also, it is found that the mass of the h^′₁(¹P₁) (mostly of sˉ) state is about 1495.18±8.82 MeV. Comparison of the predicted results and the available experimental information of the h₁(1380) shows that without further confirmation on the h₁(1380), the assignment of the h₁(1380) as the sˉ member of the ¹P₁ meson nonet may be premature.     

Hadron masses in medium and neutron star properties

We investigate the properties of the neutron star with relativistic mean-field models. We incorporate in the quantum hadrodynamics and in the quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is obtained and is employed in Oppenheimer-Volkov equation to extract the maximum mass of the stable neutron star. We find that the equation of state, the composition and the properties of the neutron stars are sensitive to the values of the meson masses in medium.     

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments. Received: 10 March 1999 / Revised version: 14 June 1999     

First measurements with the neutron decay spectrometer a SPECT

The neutron decay spectrometera SPECT has been built to perform a precise measurement of the proton spectrum shape in the decay of free neutrons. Such a measurement allows a determination of the neutrino electron angular-correlation coefficienta . The present best experiments have an uncertainty of Δa/a = 5% and since the seventies there is no substantial improvement. Witha SPECT, we aim for an uncertainty which is lower by more than an order of magnitude, thus enabling us to perform several precise tests of the Standard Model. In our first beam time at the particle physics beam MEPHISTO at the Forschungsneutronenquelle Heinz Maier-Leibnitz, we studied the properties of the spectrometer. The most serious problem turned out to be the situation- and time-dependent behavior of the background. From the data sets from this beam time in which a background problem was not obvious, we could extract a value ofa = - 0.1151±0.0040^stat , but we could not quantify the background uncertainty. We show ways to deal with the background and other problems for future beam times.     

Study of semileptonic and nonleptonic decays of the B<Subscript>c</Subscript><Superscript>-</Superscript> meson

We evaluate semileptonic and two-meson nonleptonic decays of the B _c ^- meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one-body current operators at the quark level. Our model reproduces the constraints of heavy-quark spin symmetry obtained in the limit of infinite heavy-quark mass. For the two-meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.     

Weak electric and magnetic form factors for semileptonic baryon decays in a relativistic quark model

Weak electric and magnetic form factors for semileptonic baryon decays are calculated in a relativistic quark model based on the Dirac equation with the independent-quark confining potential of the formV _q(r)=1/2(1+γ ⁰)(a ² r+V ₀). The values obtained for (g ₂/g ₁) are not very much different from the nonrelativistic results of Donoghue and Holstein. The values of (g ₁/f ₁) extracted from our model calculations of (f ₂/f ₁) in the Cabibbo limit compare well with the experimental values. The values of (f ₂/f ₁) for various semileptonic transitions are also estimated incorporating phenomenologically the effect of nonzerog ₂ in the ratio (g ₁/f ₁). It is found that the SU(3)-symmetry breaking does not generate significant departures in (f ₂/f ₁) values from the corresponding Cabibbo predictions.     

The radiative decay of $ \psi$(3770) into the predicted scalar state X(3700)

We calculate the radiative decay width of the (3770) into the dynamically generated scalar resonance X(3700) which is predicted in a previous paper. The results show that it is possible that the upgraded BEPC-II facility will generate enough statistics in order to observe this decay and thus confirm the existence of the X(3700) .     

Molecular dynamics simulation for the baryon-quark phase transition at finite baryon density

We study the baryon-quark phase transition in the molecular dynamics (MD) of the quark degrees of freedom at finite baryon density. The baryon state at low baryon density, and the deconfined quark state at high baryon density are reproduced. We investigate the equations of state of matters with different u-d-s compositions. It is found that the baryon-quark transition is sensitive to the quark width.