Octet Components Research Articles

Constructing phase space distributions with internal symmetries

We discuss an ab initio world-line approach to constructing phase space distributions in systems with internal symmetries. Starting from the Schwinger-Keldysh real time path integral in quantum field theory, we derive the most general extension of the Wigner phase space distribution to include color and spin degrees of freedom in terms of dynamical Grassmann variables. The corresponding Liouville distribution for colored particles, which obey Wong's equation, has only singlet and octet components, while higher moments are fully constrained by the Grassmann algebra. The extension of phase space dynamics to spin is represented by a generalization of the Pauli-Lubanski vector; its time evolution via the Bargmann-Michel-Telegdi equation also follows from the phase space trajectories of the underlying Grassmann coordinates. Our results for the Liouville phase space distribution in systems with both spin and color are of interest in fields as diverse as chiral fluids, finite temperature field theory and polarized parton distribution functions. We also comment on the role of the chiral anomaly in the phase space dynamics of spinning particles.

Flavor structure of Λ baryons from lattice QCD: From strange to charm quarks

We study $\mathrm{\ensuremath{\Lambda}}$ baryons of spin-parity ${\frac{1}{2}}^{\ifmmode\pm\else\textpm\fi{}}$ with either a strange or charm valence quark in full $2+1$ flavor lattice QCD. Multiple $SU(3)$ singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the $\mathrm{\ensuremath{\Lambda}}$ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and $SU(3)$ flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the $\mathrm{\ensuremath{\Lambda}}$ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest ${\frac{1}{2}}^{\ensuremath{-}}$ state, which changes from a flavor singlet $\mathrm{\ensuremath{\Lambda}}$ to a ${\mathrm{\ensuremath{\Lambda}}}_{c}$ state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity ${\mathrm{\ensuremath{\Lambda}}}_{c}$ states can be naturally explained as diquark excitations of the light $u$ and $d$ quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity $\mathrm{\ensuremath{\Lambda}}$ states, suggesting the importance of other degrees of freedom to describe them.

Color-octet contributions toxFdistributions inJ/ψhadroproduction at fixed target energies

We study $J/\ensuremath{\psi}$ production at fixed-target energies, including the color-octet production mechanisms predicted by NRQCD. In an earlier paper, we found that the octet components were crucial in understanding ${p}_{T}$-integrated forward ${(x}_{F}>0)$ cross sections. Here we make a detailed comparison of the theoretical predictions with measured ${x}_{F}$ distributions from fixed-target experiments. We find that the model predictions agree well with data. Taking into account higher orders in NRQCD, we argue that $\ensuremath{\sigma}({\ensuremath{\chi}}_{1})/\ensuremath{\sigma}({\ensuremath{\chi}}_{2})=0.6$, in excellent agreement with data. Similiar arguments also predict that $\ensuremath{\sigma}(\ensuremath{\chi})/\ensuremath{\sigma}(J/\ensuremath{\psi})$ is roughly equal in photo- and hadroproduction.

ESR study on the reactivity of two isomers of LaC82 with disilirane

We observed photochemical and thermal addition of disilirane to the LaC82-A isomer, which give new ESR active species. Both ESR spectra of the adducts in photo- and thermal reactions are well simulated by at least six octet components, and the isotropic La coupling constants and g-factors of the six octet components are determined. On the other hand, the reaction of the LaC82-B isomer with disilirane gives no ESR active species. This fact is also verified by mass spectroscopic measurements. The different reactivities with disilirane of the two isomers are not interpreted by a popular view that the two isomers have a different C82 cage structure, but we rather suggest that the origin of the isomers of metallofullerenes should be re-examined.

New metastable charmonium and the ψ′ anomaly at CDF

Production of metastable charmonium states more massive than the ψ (3685) is expected in models and could be the source of up to 50% of the ψ observed at large p T at the Tevatron. Narrow 2 −+, 2 −− c c are predicted at around 3.8 GeV and radially excited 2 3 P 1,2 may also have suppressed hadronic widths making these states potentially extra sources of ψ (3685). Colour octet components are believed to dominate ψ production at the Tevatron which suggests that hybrid charmonium production may also be prominent. Estimates of hybrid production rates and branching ratios into charmonium suggest that metastable hybrids with mass ≈4 GeV may play an important role in generating the observed ψ (3685), ψ (3095)

Non-Leptonic decays of hyperons in the quartet model

The non-leptonic hyperon decays are investigated in the framework of the colored quartet model with GIM current. We take two octet components of the weak Hamiltonian which belong to 15 and 20″ representations of SU(4) symmetry. The 15 Hamiltonian arising from the symmetry breaking is assumed to have the universal spurion coupling. We obtain remarkable fits to s- and p-wave amplitudes both in the current algebra approach and the dispersion theory. It is shown that the standard arguments for s-wave decays based on the K ∗ pole dominance, on the duality arguments and on the current algebra lead to different physical consequences with one another.

Symmetry Breaking in the Meson-Baryon System and Triangular Representations of Chiral SU(3)

We assume that the chiral-symmetry-breaking Lagrangian is an admixture of SU(3) singlet and octet components contained in a single representation $(m,\overline{m})+(\overline{m},m)$ of SU(3) \ifmmode\times\else\texttimes\fi{} SU(3). If we restrict ourselves to the case in which ($m$) is any triangular representation of SU(3), we find that, except for the triplet, all such symmetry-breaking Lagrangians are inconsistent with present data on meson-baryon $\ensuremath{\sigma}$ terms. Thus the only irreducible representation that may be consistent is the (3,\ifmmode\bar\else\textasciimacron\fi{}3) + (\ifmmode\bar\else\textasciimacron\fi{}3,3).

Nonlepton four-fermion interactions with ?S = 1, SU3 symmetry, and RP invariance

It is assumed that the Lagrangian for the weak interactions of hadrons has the transformation properties of octet components and is RP invariant; relations are deduced between the amplitudes of the four-fermion nonlepton with ΔS = 1. Information on such interactions may be derived from mesonless decays of various hypernuclei.

Special Permutation Invariants of FourSU3Octets

A simple proof is given that a biquadratic form of octets exists which is a scalar under $S{U}_{3}$, an eigenvector of the permutation operator ${p}_{13}$ (and ${p}_{24}$), and whose constituent quadratics transform like octet components. The form is given and so is another, subject only to the last two conditions.