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Results for “MESON-MESON INTERACTIONS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Tetraquark operators in lattice QCD and exotic flavour states in the charm sector

We present a general class of operators resembling compact tetraquarks which have a range of colour-flavour-spin structures, transform irreducibly under the symmetries of the lattice and respect other relevant symmetries. These constructions are demonstrated in lattice QCD calculations with light quarks corresponding to m π = 391 MeV. Using the distillation framework, correlation functions involving large bases of meson-meson and tetraquark operators are computed in the isospin-1 hidden-charm and doubly-charmed sectors, and finite-volume spectra are extracted with the variational method. We find the spectra are insensitive to the addition of tetraquark operators to the bases of meson-meson operators. For the first time, through using diverse bases of meson-meson operators, the multiple energy levels associated with meson-meson levels which would be degenerate in the non-interacting limit are extracted reliably. The number of energy levels in each spectrum is found to be equal to the number of expected non-interacting meson-meson levels in the energy region considered and the majority of energies lie close to the non-interacting levels. Furthermore, there is no strong indication for any bound state or narrow resonance in the channels we study.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Vector and axial anomaly in the Thirring-Wess model

We study the two dimensional vector meson model introduced by Thirring and Wess, that is to say the Schwinger model with massive photon and massless fermion. We prove, with a renormalization group approach, that the vector and axial Ward identities are broken by the Adler-Bell-Jackiw anomaly; and we rigorously establish three widely believed consequences: (a) the interacting meson-meson correlation equals a free boson propagator, although the mass is additively renormalized by the anomaly; (b) the anomaly is quadratic in the charge, in agreement with the Adler-Bardeen formula; (c) the fermion-fermion correlation has an anomalous long-distance decay.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Lattice investigation of nucleon structure at light quark masses

Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes at, e.g. Jefferson Lab, COMPASS/CERN and FAIR/GSI. By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this exciting area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of ordinary parton distribution functions, show some indication of approaching their phenomenological values.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

QMC and the nature of dense matter: written in the stars?

We discuss the recent progress in calculating the properties of 'hybrid stars'(stellar objects similar to neutron stars, classified by the incorporation of non-nucleonic degrees of freedom, including but not limited to hyperons and/or a quark-matter core) using the octet-baryon Quark-Meson Coupling (QMC) model. The version of QMC used is a recent improvement which includes the in-medium modification of the quark-quark hyperfine interaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Strangeness in the Meson Cloud Model

I review progress in calculating strange quark and antiquark distributions of the nucleon using the meson cloud model. This progress parallels that of the meson cloud model, which is now a useful theoretical basis for understanding symmetry breaking in nucleon parton distribution functions. I examine the breaking of symmetries involving strange quarks and antiquarks, including quark--antiquark symmetry in the sea, SU(3) flavour symmetry and SU(6) spin-flavour symmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

From the nucleus to the quarks

Early work by A. W. Thomas and his colleagues inspired the first measurements of polarization in pion-deuteron elastic scattering. This line of research and technology developments enabled polarization experiments in electron-deuteron elastic scattering as well as the widespread use of polarized internal targets in storage rings. These ideas and techniques are now being used to study two-photon exchange effects and to make progress toward experiments that will allow for improved extractions the d/u ratio at high x.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Unitarized Chiral Perturbation Theory and the meson spectrum

In this talk we briefly review how the unitarization of Chiral Perturbation Theory with dispersion relations can successfully describe the meson-meson scattering data and generate light resonances, whose mass, width and nature can be related to QCD parameters like quark masses and the number of colors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Vector meson-vector meson interaction and dynamically generated resonances

Using the local hidden gauge formalism for the vector meson-vector meson interaction within a unitary approach we find that 11 states get dynamically generated. Five of them are associated to the f{sub 0}(1370), f{sub 0}(1710), f{sub 2}(1270), f{sub 2}'(1525), and K{sub 2}*(1430) resonances, by comparing the mass, width, and decay pattern of these states with those of their experimental counterparts. At the same time we predict six other states with the quantum numbers of h{sub 1}, a{sub 0}, b{sub 1}, a{sub 2}, K{sub 0}*, and K{sub 1} which could be tested by future experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

On how once subtracted dispersion relations lead to a precise determination of {pi}{pi} scattering and the f{sub 0}(600) parameters

We present and compare once and twice subtracted dispersion relations including crossing symmetry constraints in order to test the S- and P-wave {pi}{pi} amplitudes below 1100 MeV. We show that twice subtracted dispersion relations provide stringent constraints on the {pi}{pi} amplitudes below about 400 MeV than those with one subtraction. Above this energy GKPY eqs. become, however, a more demanding test of {pi}{pi} amplitudes, thus providing a new tool for the precise determination of {pi}{pi} scattering. We also show that due to strong constraints imposed by the GKPY eqs. they are useful for the determination of the f{sub (600)} pole position with high accuracy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

The covalent bond in Particle Spectroscopy

Meson resonances are linear combinations of qq-bar and meson-meson (MM) baryon resonances are combinations of qqq and meson-baryon. Mixing between these combinations arises via decays of confined states to meson-meson or meson-baryon. There is a useful analogy with the covalent bond in molecular physics. One eigenstate is lowered by the mixing. Cusps arise at thresholds. At sharp thresholds due to S-wave 2-particle decays, these cusps play a conspicuous role in many sets of data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Charmonium molecules?

In this talk we present some recent studies of multiquark components in the charmonium sector. We study the possible existence of compact four quark-states and meson-meson molecules in the charmonium spectroscopy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Meson-Meson molecules and compact four-quark states

The physics of charm has become one of the best laboratories exposing the limitations of the naive constituent quark model and also giving hints into a more mature description of meson spectroscopy, beyond the simple quark-antiquark configurations. In this talk we review some recent studies of multiquark components in the charm sector and discuss in particular exotic and non-exotic four-quark systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Structure of the lightest scalar meson from the 1/N{sub c} expansion of Unitarized Chiral Perturbation Theory and Regge Theory

One-loop unitarized Chiral Perturbation Theory (UChPT) calculations, suggest a different Nc behaviour for the {sigma} or f{sub 0}(600) and {rho}(770) mesons: while the {rho} meson becomes narrower with Nc, as is expected for a q-barq meson, the {sigma} becomes broader, and its contribution to the total cross section is less and less important. On the other hand, local duality requires a cancellation between the {sigma} and {rho} amplitudes, but if there is a different Nc behaviour for them, there is a possible contradiction between the Inverse Amplitude Method (IAM) and local duality for large Nc. However, next to next to leading order UChPT calculations suggested a subdominant q-barq component for the {sigma} with a mass around 1.2 GeV. In this work, we show that this subdominant q-barq component is indeed needed to ensure local duality.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

The Search for Exotic Mesons in {gamma}p{yields}{pi}{sup +{pi}+{pi}-}n with CLAS at Jefferson Lab

In addition to ordinary qq-bar pairs, quantum chromodynamics (QCD) permits many other possibilities in meson spectra, such as gluonic hybrids, glueballs, and tetraquarks. Experimental discovery and study of these exotic states provides insight on the nonperturbative regime of QCD. Over the past twenty years, some searches for exotic mesons have met with controversial results, especially those obtained in the three-pion system. Prior theoretical work indicates that in photoproduction one should find gluonic hybrids at significantly enhanced levels compared to that found in pion production. To that end, the CLAS g12 run was recently completed at Jefferson Lab, using a liquid hydrogen target and tagged photons from a 5.71 GeV electron beam. The CLAS experimental apparatus was modified to maximize forward acceptance for peripheral production of mesons. The resulting data contains the world's largest 3{pi} photoproduction dataset, with {gamma}p{yields}{pi}{sup +{pi}+{pi}-}n events numbering in the millions. Early results describing the data quality, kinematics, and dysnamics will be shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

f{sub 0}(600),{kappa}(800), {rho}(770) and K*(892), quark mass dependence from unitarized SU(3) Chiral Perturbation Theory

We study the strange and non-strange quark mass dependence of the parameters of the f{sub 0}(600),{kappa}(800), {rho}(770) and K*(892) resonances generated from elastic meson-meson scattering using unitarized one-loop Chiral Perturbation Theory. We fit simultaneously all experimental scattering data up to 0.8-1 GeV together with lattice results on decay constants and scattering lengths up to a pion mass of 440 MeV. Then, the strange and non-strange quark masses are varied from the chiral limit up to values of interest for lattice studies. In these amplitudes, the mass and width of the {rho}(770) and K*(892) present a similar and smooth quark mass dependence. In contrast, both scalars present a similar non-analyticity at high quark masses. Nevertheless the f{sub 0}(600) dependence on both quark masses is stronger than for the {kappa}(800) and the vectors. We also confirm the lattice assumption of quark mass independence of the vector two-meson coupling that, in contrast, is violated for scalars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Systematic Study of Two-Pion Production in NN Collisions--from Single-Baryon to Di-Baryon Excitations

The two-pion production in nucleon-nucleon collisions has been studied by exclusive and kinematically complete experiments from threshold up to T{sub p} = 1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential distributions for the {pi}{sup +{pi}-} and {pi}{sup 0{pi}0} channels are dominated by Roper excitation and its decay into N{sigma}s and {Delta}{pi} channels. At beam energies T{sub p}>1.1 GeV the {Delta}{Delta} excitation governs the two-pion production process. In the {pi}{sup +{pi}+} channel evidence is found for the excitation of a higher-lying I =3/2 resonance, favorably the {Delta}(1600). The isovector fusion processes leading to the deuteron and to quasi-stable {sup 2}He, respectively, exhibit no or only a modest ABC-effect, i.e. low-mass enhancement in the {pi}{pi}-invariant mass spectrum, and can be described by conventional t-channel {Delta}{Delta} excitation. On the other hand, the isoscalar fusion process to the deuteron exhibits a dramatic ABC-effect correlated with a narrow resonance-like energy dependence in the total cross section with a width of only 50 MeV and situated at a mass 90 MeV below the {Delta}{Delta} mass.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗