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We present experimental results from the BaBar experiment on charm baryon spectroscopy and production studies, including studies of excited cascades produced in charm baryon decays. We review the discovery of new decay modes of known states and searches for predicted states.
Three-quark nucleon interpolating fields in QCD have well-defined SU{sub L}(3)xSU{sub R}(3) and U{sub A}(1) chiral transformation properties, viz. [(6,3)+(3,6)], [(3,3-bar)+(3-bar,3)], [(8,1)+(1,8)] and their 'mirror' images. It has been shown (phenomenologically) in Ref. [2] that mixing of the [(6,3)+(3,6)] chiral multiplet with one ordinary ('naive') and one 'mirror' field belonging to the [(3,3-bar)+(3-bar,3)], [(8,1)+(1,8)] multiplets can be used to fit the values of the isovector (g{sub A}{sup (3)}) and the flavor-singlet (isoscalar) axial coupling (g{sub A}{sup (0)}) of the nucleon and then predict the axial F and D coefficients, or vice versa, in reasonable agreement with experiment. In an attempt to derive such mixing from an effective Lagrangian, we construct all SU{sub L}(3)xSU{sub R}(3) chirally invariant non-derivative one-meson-baryon interactions and then calculate the mixing angles in terms of baryons' masses. It turns out that there are (strong) selection rules: for example, there is only one non-derivative chirally symmetric interaction between J 1/2 fields belonging to the [(6,3)+(3,6)] and the [(3,3-bar)+(3-bar,3)] chiral multiplets, that is also U{sub A}(1) symmetric. We also study the chiral interactions of the [(3,3-bar)+(3-bar,3)] and [(8,1)+(1,8)] nucleon fields. Again, there are selection rules that allow only one off-diagonal non-derivative chiral SU{sub L}(3)xSU{sub R}(3) interaction of this type, that also explicitly breaks the U{sub A}(1) symmetry. We use this interaction to calculate the corresponding mixing angles in terms of baryon masses and fit two lowest lying observed nucleon (resonance) masses, thus predicting the third (J = 1/2, I = 3/2){Delta} resonance, as well as one or two flavor-singlet {Lambda} hyperon(s), depending on the type of mixing. The effective chiral Lagrangians derived here may be applied to high density matter calculations.
Exotic hadrons with heavy quarks can confirm in the same multiquark system that the qq-bar interaction is much stronger than the qq interaction and produces color structures totally different from those of normal hadrons. Unusual heavy tetraquark structure may explain unusual properties of newly discovered mesons like the X(3872). Both charged and neutral B decays produce this narrow neutral resonant state that decays to both J/{psi}{rho} and J/{psi}{omega}, while no charged resonances in the same multiplet are found. This suggests that the X is an isoscalar resonance whose production conserves isospin, while isospin is violated only in the decay by an electromagnetic interaction allowing the isospin-forbidden J/{psi}{rho} decay. New data for X production in B decays provide a separation between production and decay, sharpen several experimental puzzles and impose serious constraints on all models. A proposed isoscalar tetraquark model agrees with all present data, conserves isospin in its production and breaks isospin only in an electromagnetic X(3872)J/{psi}{rho}{sup o} decay. The narrow X decay width results from the tiny phase space available for the J/{psi}{omega} decay and enables competition with the electromagnetic isospin-forbidden J/{psi}{rho} decay which has much larger phase space. Experimental tests are proposed for this isospin production invariance.
{Lambda}{sub c}N bound state problem is investigated in the one-meson-exchange potential model. The potentials are obtained from an effective Lagrangian reflecting the heavy quark symmetry, chiral symmetry, and hidden local symmetry. We also consider the contributions from the coupled channels of {Sigma}{sub c}N and {Sigma}{sub c}*N. It is found that the channel coupling is very important in binding the baryons. We find that the formation of the nearly degenerate J{sup P} = 0{sup +} and J{sup P} = 1{sup +} {Lambda}{sub c}N molecular bound states is plausible, although the results are sensitive to the cutoff parameters.
A description of fragmentation processes of quarks into hadrons is presented in the framework of the recently developed NJL-jet model, where the momentum and isospin sum rules are satisfied naturally. We present the results for pion, kaon and nucleon fragmentation functions, and compare the results with the empirical functions.
The pion final state interaction model in NEUT is described. Modifications and tuning of the model are validated against neutrino and non-neutrino (pion scattering and photoproduction) data. A method for evaluating the uncertainties in the model and propagation of systematic errors in a neutrino oscillation experiment is described, using T2K as a specific example.
The nonperturbative Hamiltonian eigenvalue problem for bound states of a quantum field theory is formulated in terms of Dirac's light-front coordinates and then approximated by the exponential-operator technique of the many-body coupled-cluster method. This approximation eliminates any need for the usual approximation of Fock-space truncation. Instead, the exponentiated operator is truncated, and the terms retained are determined by a set of nonlinear integral equations. These equations are solved simultaneously with an effective eigenvalue problem in the valence sector, where the number of constituents is small. Matrix elements can be calculated, with extensions of techniques from standard coupled-cluster theory, to obtain form factors and other observables.
We study the motion of an electron and emission of electromagnetic waves by an electron in the field of a relativistically intense laser pulse. The dynamics of the electron is described by the Newton equation with the Lorentz force in the right-hand side. It is shown that the electrons may be ejected from the interaction region with high energy. The energy spectrum of these electrons and the technique of using the spectrum to assess the maximal intensity in the focus are analysed. It is found that electromagnetic radiation of an electron moving in an intense laser field occurs within a small angle around the direction of the electron trajectory tangent. The tangent quickly changes its direction in space; therefore, electromagnetic radiation of the electron in the far-field zone in a certain direction in the vicinity of the tangent is a short pulse with a duration as short as zeptoseconds. The calculation of the temporary and spectral distribution of the radiation field is carried out. (superintense laser fields)
A measurement for studying the mass dependence of dilepton interferometry in relativistic heavy-ion collision experiments as a tool to characterize the quark gluon phase is proposed. In calculations involving dileptons, we show that the mass dependence of radii extracted from the virtual photon (dilepton) interferometry provide access to the development of collective flow with time. It is argued that the nonmonotonic variation of Hanbury Brown-Twiss radii with invariant mass of the lepton pairs signals the formation of quark gluon plasma in heavy ion collisions. Our proposal of experimentally measuring the ratio, R{sub out}/R{sub side} for dileptons can be used to estimate the average lifetimes of the partonic as well as the hadronic phases.
We estimate the long-distance contribution to the width difference of the B{sub s}-B{sub s} system, based mainly on two-body D{sub s}{sup (*)}D{sub s}{sup (*)} modes and three-body D{sub s}{sup (*)}D{sup (*)}K{sup (*)} modes (and their CP conjugates). Some higher cs resonances are also considered. The contribution to {Delta}{Gamma}{sub s}/{Gamma}{sub s} by two-body modes is (10.2{+-}3.0)%, slightly smaller than the short-distance result of (13.3{+-}3.2)%. The contribution to {Delta}{Gamma}{sub s}/{Gamma}{sub s} by D{sub s0}*(2317), D{sub s1}(2460), and D{sub s1}(2536) resonances is negligible. For the three-body D{sub s}{sup (*)}D{sup (*)}K{sup (*)} modes, we adopt the factorization formalism and model the form factors with off-shell D{sub s}{sup (*)} poles, the D{sub sJ}(2700) resonance, and nonresonant contributions. These three-body modes can arise through current-produced or transition diagrams, but only SU(3)-related D{sub u,d}{sup (*)}D{sup (*)}K modes from the current diagram have been measured so far. The pole model results for D{sub u,d}*D{sup (*)}K agree well with the data, while D{sub u,d}D{sup (*)}K rates agree with the data only within a factor of 2 to 3. All measured D{sub u,d}{sup (*)}D{sup (*)}K rates can be reproduced by including nonresonant contributions. The total {Delta}{Gamma}{sub s}/{Gamma}{sub s} obtained is (16.7{+-}8.5)%, which agrees with the short-distance result within uncertainties. For illustration, we also demonstrate the effect of D{sub sJ}(2700) in modes with D{sup (*)}K{sup *}. In all scenarios, the total {Delta}{Gamma}{sub s}/{Gamma}{sub s} remain consistent with the short-distance result. Our results indicate that (a) the operator product expansion in the short-distance picture is a valid assumption, (b) approximating the B{sub s}{yields}D{sub s}{sup (*)}D{sub s}{sup (*)} decays to saturate {Delta}{Gamma}{sub s} has a large correction, (c) the effect of three-body modes cannot be neglected, and (d) in addition to the D{sub s} and D{sub s}* poles, the D{sub sJ}(2700) resonance also plays an important role in three-body modes. Future experiments are necessary to improve the estimation of {Delta}{Gamma}{sub s} from the long-distance point of view.
The one-loop quark contribution to the QCD effective potential for the homogeneous Abelian gluon field in the presence of an external strong electromagnetic field is evaluated. The structure of extrema of the potential as a function of the angles between chromoelectric, chromomagnetic, and electromagnetic fields is analyzed. In this setup, the electromagnetic field is considered as an external one while the gluon field represents domain structured nonperturbative gluon configurations related to the QCD vacuum in the confinement phase. Two particularly interesting gluon configurations, (anti-)self-dual and crossed orthogonal chromomagnetic and chromoelectric fields, are discussed specifically. Within this simplified framework it is shown that the strong electromagnetic fields can play a catalyzing role for a deconfinement transition. At the qualitative level, the present consideration can be seen as a highly simplified study of an impact of the electromagnetic fields generated in relativistic heavy ion collisions on the strongly interacting hadronic matter.
We show that simultaneous precision measurements of the CP-violating phase in time-dependent B{sub s}{yields}J/{psi}{phi} study and the B{sub s}{yields}{mu}{sup +}{mu}{sup -} rate, together with measuring m{sub t'} by direct search at the LHC, would determine V{sub t's}*V{sub t'b} and therefore the b{yields}s quadrangle in the four-generation standard model. The forward-backward asymmetry in B{yields}K*l{sup +}l{sup -} provides further discrimination.
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