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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 163 records · Page 9
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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.

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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.

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DOE OSTI2010

Study of {pi}{sup -}p{yields}{pi}{sup -{eta}p} and {pi}{sup -}p{yields}{pi}{sup -{eta}{eta}}p at {radical}(s) = 18.9 GeV with the COMPASS experiment

The COMPASS experiment at CERN studies diffractively produced states in the light quark sector with unprecedented statistics. The observation of f{sub 0}(1500)/f{sub 2}'(1525) decaying to {eta}{eta} in 2008 data with incoming negative pion beam at 190 GeV/c poses the question whether it is produced centrally or formed by the decay of a heavier diffractively produced {pi}{sub 1}(1800)/{pi}{sub 2}(1880). To decide, a dedicated amplitude analysis which includes different production mechanisms is formulated and compared with one which was used to fit centrally produced resonances including f{sub 0}(1500) by the WA102 experiment. Unbinned mass-dependent log-likelihood fitting methods may serve to solve the ambiguities which are present in binned, mass-independent partial wave analyses.

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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.

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DOE OSTI2010

Kaon pair production in pp, pd and dd collisions at COSY

The near-threshold production of kaon-pairs has been investigated in proton-proton, proton-deuteron and deuteron-deuteron collisions at the Cooler Synchrotron COSY. The excitation function for the pp{yields}ppK{sup +}K{sup -} reaction and the invariant K{sup -}p, K{sup -}pp, and K{sup +}K{sup -} mass distributions indicate the presence of both K{sup -}p and K{sup +}K{sup -} final state interactions. Analogous final-state interactions of antikaons with deuterons has been found in the pp{yields}dK{sup +}K{sup 0}-bar reaction as well as in the pn{yields}dK{sup +}K{sup -} reaction, measured in the quasi-free pd{yields}p{sub sp}dK{sup +}K{sup -} process with a 'spectator' proton (p{sub sp}). The existing COSY data on the pd{yields}{sup 3}HeK{sup +}K{sup -} reaction are not yet sufficient to study the K{sup -3}He and K{sup +}K{sup -} final state interactions. A very small total cross section was found for the dd{yields}{sup 4}HeK{sup +}K{sup -} reaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Nucleon-Nucleon Interactions from the Quark Model

We report on investigations of the applicability of non-relativistic constituent quark models to the low-energy nucleon-nucleon (NN) interaction. The major innovations of a resulting NN potential are the use of the {sup 3}P{sub 0} decay model and quark model wave functions to derive nucleon-nucleon-meson form-factors, and the use of a colored spin-spin contact hyperfine interaction to model the repulsive core rather than the phenomenological treatment common in other NN potentials. We present the results of the model for experimental free NN scattering phase shifts, S-wave scattering lengths and effective ranges and deuteron properties. Plans for future study are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Hadron Spectroscopy in Double Pomeron Exchange Processes with the STAR Detector at RHIC

A new hadron spectroscopy program to study particle production at the central region through diffractive processes in polarized p+p collisions at {radical}(s) = 200-500 GeV has been initiated with the STAR detector at RHIC. Staged implementation of multiple Roman Pot stations for tagging forward protons in diffractive processes allows studying for the first time the dynamics of the particle production in the diffractive processes systematically at the RHIC energy regime. The STAR detector system with complete azimuthal coverage at the central region equipped with excellent particle reconstruction capabilities enables studies of the constituent gluonic degree of freedom in double Pomeron exchange processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Hunting for a new {Sigma}*(1/2{sup -}) resonance around 1380 MeV

Quenched and unquenched quark models give very distinctive predictions for the lowest {Sigma}* with spin-parity J{sup P} = 1/2{sup -}. We report evidence for possible existence of a new {Sigma}* resonance with J{sup P} = 1/2{sup -} around 1380 MeV by re-examining data of various relevant reactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Negative Parity Baryon Decays in the 1/N{sub c} Expansion

The 1/N{sub c} expansion of QCD provides a useful framework for phenomenological studies of both ground state and excited baryons. Here, we focus on its application to the excited baryon strong decays via emission of single pseudoscalar meson. The S- and D-wave decay amplitudes of the negative parity baryons in the [70,1{sup -}] of SU(6) are analyzed to subleading order in 1/N{sub c} and to first order in SU(3) symmetry breaking. In particular, the SU(3) symmetry breaking is studied in detail through SU(3) breaking decay operators and state mixing.

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DOE OSTI2010

Photoproduction of the {Lambda}*(1520) Hyperon

The photoproduction of the {Lambda}*(1520) on both the proton and neutron have been studied by using the CLAS eg3 run data set. The reactions are {gamma}d{yields}K{sup +{Lambda}}*(n) and {gamma}d{yields}K{sup 0{Lambda}}*(p) with {Lambda}*{yields}pK{sup -}. Preliminary total and differential cross sections have been extracted in the photon energy region 1.75 GeV<E{sub {gamma}<}5.50 GeV. This is the first time that the photoproduction of {Lambda}*(1520) on the neutron is reported, and we will extend the results on the proton to higher energies than in previous studies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Photoproduction of {Sigma}{sup +}K{sub s}{sup 0} with the CBELSA/TAPS-setup

Albeit quark models explain the known baryon spectrum reasonably well, they all overpredict the number of states significantly. This is often called the 'missing resonance' problem. It is speculated, that some of these resonances remained undetected in pi-induced reactions, but have a sizeable coupling to channels with strangeness involved. This provided our motivation to measure cross sections and polarisation observables in associated Kaon-Hyperon photoproduction with the focus on the {Sigma}{sup +}K{sub s}{sup 0} channel. Up to now, for this particular channel only limited data exists from the SAPHIR-, CLAS- and CBELSA/TAPS-collaboration for total and differential cross sections, and for recoil polarisation. Using the linearly polarised, energy tagged photon beam at the ELSA particle accelerator of Bonn University, data were taken with the combined photon spectrometers Crystal Barrel and TAPS. This setup is well suited to detect multi photon final states and therefore ideal to measure the reaction channel {gamma}p{yields}{Sigma}{sup +}K{sub s}{sup 0{yields}}p{pi}{sup 0{pi}0{pi}0{yields}}p6{gamma}. Here the extraction of cross sections, the recoil polarisation P and the photon asymmetry {Sigma}, which is measured for the first time, will be discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

K*{sup 0}(892){Lambda} and K{sup +{Sigma}-}(1385) Photoproduction on the Deuteron

Measurement of the spectrum of excited baryons and their decay is an important part of the effort to understand the structure of the nucleon. Coupled-channel analyses of pion, eta, and kaon production reactions are capable of extracting more information on the excited baryon resonances than a partial-wave analysis of each of the reactions individually. These will result in improved quark model predictions of the large mass N* states, where wide resonances and insufficient data make it difficult to differentiate the states from the background. These analyses are also an important part of understanding the effective degrees of freedom of the nucleon and will provide a better understanding of QCD.In the past several years, extensive work has been done on measuring cross sections and polarization observables of the kaon production reactions on the proton. To complement these data, the CLAS g13 experiment at Jefferson Lab collected 50 billion events on deuterium using circularly and linearly polarized photon beams. Along with studying the kaon production reactions on the neutron, the excited kaon and excited hyperon channels are being studied as well.It has been predicted that the s-channel production of the {gamma}n{yields}K*{sup 0}(892){Lambda} and {gamma}n{yields}K{sup +{Sigma}-}(1385) reactions will couple non-negligibly to the decays of several of the excited N* states. These include the N*(1495), N*(2070), and N*(2090) for K*{sup 0}(892){Lambda} production, and the N*(1980) and N*(2095) for K{sup +{Sigma}-}(1385) production [1]. With data from the CLAS g13 experiment, preliminary results from studies of the {gamma}D{yields}K*{sup 0}(892){Lambda}(p) and {gamma}D{yields}K{sup +{Sigma}-}(1385)(p) reactions will be shown.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Vector baryon interaction and dynamically generated resonances

The formalism for the interaction of vector mesons with baryons within the local hidden gauge formalism is presented and it is shown to lead to a large amount of dynamically generated baryonic resonances, many of which can be associated to known states, while others represent predictions for new resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Longitudinal and Transverse Parton Momentum Distributions for Hadrons within Relativistic Constituent Quark Models

Longitudinal and transverse parton distributions for pion and nucleon are calculated from hadron vertexes obtained by a study of form factors within relativistic quark models. The relevance of the one-gluon-exchange dominance at short range for the behavior of the form factors at large momentum transfer and of the parton distributions at the end points is stressed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Studying Hadron Properties in Baryonic Matter with HADES

The HADES spectrometer installed at GSI Darmstadt is a second generation experiment to study production of lepton pairs from proton, pion and nucleus induced reactions at the SIS/BEVALAC energy regime. The HADES study of the light C+C system at 1 and 2 AGeV confirms former finding of the DLS collaboration. Further studies of the reaction p+p and d+p allowed to reveal contribution to the above mentioned data of di-leptons produced during first chance collision. Finally, the results of the study of heavier system Ar+KCl indicates possible nonlinear dependence of the observed excess over the known long lived sources of di-leptons on the number of participants.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Study of electromagnetic processes with the dielectron spectrometer HADES

Dielectron production in pp and dp reactions at 1.25 A.GeV has been studied with the High Acceptance DiElectron Spectrometer (HADES) at GSI. Results obtained in inclusive and exclusive channels are shown, along with {pi}{sup +}, {pi}{sup -} and {eta} production in pp reactions at 1.25 and 2.2 GeV. Perspectives of experiments with {pi}{sup -} beams are outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Inclusive meson production in 3.5 GeV pp collisions studied with the HADES spectrometer

We present the inclusive di-electron invariant-mass spectrum from p+p interactions at 3.5 GeV kinetic beam energy. It is a very important reference for the study of vector meson production off the nucleus, recently investigated by HADES in p+{sup 93}Nb reactions at the same beam energy. Up to invariant masses of 0.6 GeV/c{sup 2} the main contributions to the e{sup +}e{sup -} spectrum are {pi}{sup 0},{eta}, {omega} and {Delta} Dalitz decays. In the vector-meson region a clear peak corresponding to the {omega} direct decay is reconstructed with {approx_equal}2% mass resolution. Subtracting this peak from the spectrum allows to investigate additional sources, in particular the {rho} meson. Indeed, the latest results from HSD and UrQMD calculations show different distributions for the shape of the {rho} meson at these energies. Therefore it is important to experimentally understand the production mechanism of the {rho} meson in elementary reactions. Besides the spectral shape of the mesons, their inclusive production cross sections are also not known at these energies. Due to the large and flat acceptance of the HADES spectrometer for e{sup +}e{sup -} masses above 0.2 GeV/c{sup 2} and for P{sub T}<1GeV/c, acceptance corrections are to a large extent model independent. This allows us to extract the preliminary inclusive cross section values for the meson productions at these energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗