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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 289 records · Page 16
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DOE OSTI2011

Single-energy amplitudes for pion photoproduction in the first resonance region

We consider multipole amplitudes for low-energy pion photoproduction, constructed with minimal model dependence, at single energies. A previous fit making minimal use of Watson's theorem has been reexamined in light of more recent measurements. Problems associated with the choice of a unique solution are discussed. Comparisons with more recent fits to the full resonance region are made. Explanations are suggested for the discrepancies and more precise measurements of the recoil polarization, P, are motivated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Two-photon fusion in high-energy electron-nucleus scattering

Experimental studies of meson production through two-photon fusion in inelastic electron-nucleus scattering are now under way. A high-energy photon radiated by the incident electron is fused with a soft photon radiated by the nucleus to create the meson. The process takes place in the small-angle Coulomb region of nuclear scattering. We expound the theory for this production process as well as its interference with coherent-radiative-meson production. In particular, we investigate the distortion of the electron wave function due to multiple-Coulomb scattering.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Photo- and electroproduction of K{sup 0{Lambda}} near threshold and effects of the K{sup 0} electromagnetic form factor

By extending our previous isobar model to the K{sup 0{Lambda}} isospin channel, we investigate the properties of the K{sup 0{Lambda}} photo- and electroproduction at energies near threshold. It is found that the pseudovector coupling yields significantly larger cross sections. Variation of the K{sub 1} coupling constants has significant effect only on the pseudovector model. The electromagnetic form factor of the neutral kaon K{sup 0} is found to have a sizable effect on the longitudinal cross section of the K{sup 0{Lambda}} electroproduction near the threshold.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Photoproduction of Z(4430) through mesonic Regge trajectories exchange

The recently discovered Z(4430) mesonic resonance is believed to be a strong tetraquark candidate. The photoproduction in the channel {gamma}p{yields}Z{sup +}(4430)n{yields}{psi}{sup '}{pi}{sup +}n has been proposed as the most effective way to confirm the Z(4430) presence and to measure its quantum numbers. In this work we present a model for high-energy and forward-angle Z(4430) photoproduction in a effective Lagrangian approach. This model is based on the use of Regge trajectories exchange, thus a Regge propagator replaces the usual Feynman propagator. The differential and total cross sections and the asymmetries have been calculated for the J{sup P} quantum numbers 1{sup -}, 1{sup +}, 0{sup -}, and 2{sup -} in the hypotheses where Z(4430) has isospin I=1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Dressing the electromagnetic nucleon current

A field-theory-based approach to pion photoproduction off the nucleon is used to derive a microscopically consistent formulation of the fully dressed electromagnetic nucleon current in an effective Lagrangian formalism. It is shown how the rigorous implementation of local gauge invariance at all levels of the reaction dynamics provides equations that lend themselves to practically manageable truncations of the underlying nonlinearities of the problem. The requirement of consistency also suggests a novel way of treating the pion photoproduction problem. Guided by a phenomenological implementation of gauge invariance for the truncated equations that has proved successful for pion photoproduction, an expression for the fully dressed nucleon current is given that satisfies the Ward-Takahashi identity for a fully dressed nucleon propagator as a matter of course. Possible applications include meson photo- and electroproduction processes, bremsstrahlung, Compton scattering, and ee{sup '} processes off nucleons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Possibility of observing an MSSM charged Higgs boson in association with a W boson at the LHC

The possibility of observing associated production of the charged Higgs and W boson in the framework of the minimal supersymmetric standard model (MSSM) at LHC is studied. Both leptonic and hadronic decays of the W boson are studied while the charged Higgs boson is considered to decay to a {tau} lepton and a neutrino. Therefore two search categories are defined based on the leptonic and hadronic final states, i.e., l{tau}+E{sub T}{sup miss} and jj{tau}+E{sub T}{sup miss} where l=e or {mu} and j is a light jet from W decay. The discovery chance of the two categories is evaluated at an integrated luminosity of 300 fb{sup -1} at LHC. It is shown that both leptonic and hadronic final states have the chance of discovery at high tan{beta}. Finally 5{sigma} and 3{sigma} contours are provided for both search categories.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Yukawa coupling and anomalous magnetic moment of the muon: An update for the LHC era

We study the interplay between a soft muon Yukawa coupling generated radiatively with the trilinear A-terms of the minimal supersymmetric standard model (MSSM) and the anomalous magnetic moment of the muon. In the absence of a tree-level muon Yukawa coupling the lightest smuon mass is predicted to be in the range between 600 GeV and 2200 GeV at 2{sigma}, if the bino mass M{sub 1} is below 1 TeV. Therefore, a detection of a smuon (in conjunction with a sub-TeV bino) at the LHC would directly imply a nonzero muon Yukawa coupling in the MSSM superpotential. Inclusion of slepton flavor mixing could in principle lower the mass of one smuonlike slepton below 600 GeV. However, the experimental bounds on radiative lepton decays instead strengthen the lower mass bound, with larger effects for smaller M{sub 1}, We also extend the analysis to the electron case and find that a light selectron close to the current experimental search limit may prove the MSSM electron Yukawa coupling to be nonzero.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Phenomenological constraints on minimally coupled exotic lepton triplets

By introducing a set of new triplet leptons (with nonzero hypercharge) that can Yukawa couple to their standard model counterparts, new sources of tree-level flavor changing currents are induced via mixing. In this work, we study some of the consequences of such new contributions on processes such as the leptonic decays of gauge bosons, l{yields}3l{sup '} and l{yields}l{sup '{gamma}}, which violate lepton flavor, and {mu}-e conversion in atomic nuclei. Constraints are then placed on the parameters associated with the exotic triplets by invoking the current low-energy experimental data. Moreover, the new physics contribution to the lepton anomalous magnetic moments is calculated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Model-independent constraints on the shape parameters of dilepton angular distributions

The coefficients determining the dilepton decay angular distribution of vector particles obey certain positivity constraints and a rotation-invariant identity. These relations are a direct consequence of the covariance properties of angular momentum eigenstates and are independent of the production mechanism. The Lam-Tung relation can be derived as a particular case, simply recognizing that the Drell-Yan dilepton is always produced transversely polarized with respect to one or more quantization axes. The dilepton angular distribution continues to be characterized by a frame-independent identity also when the Lam-Tung relation is violated. Moreover, the violation can be easily characterized by measuring a one-dimensional distribution depending on one shape coefficient.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Precise predictions for (nonstandard) W{gamma}+ jet production

We report on a detailed investigation of the next-to-leading-order QCD corrections to W{gamma}+jet production at the Tevatron and the LHC using a fully flexible parton-level Monte Carlo program. We include the full leptonic decay of the W, taking into account all off-shell and finite width effects, as well as nonstandard WW{gamma} couplings. We find particularly sizable corrections for the currently allowed parameter range of anomalous couplings imposed by LEP data. In total, the next-to-leading-order differential distributions reveal a substantial phase-space dependence of the corrections, leaving considerable sensitivity to anomalous couplings beyond scale uncertainty at large momentum transfers in the anomalous vertex.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Scheme for the extraction of WIMP-nucleon scattering cross sections from total event rates

We propose a scheme that allows to analytically determine the three elementary cross sections and connect the solutions to the relative sign between the proton and the neutron spin scattering amplitudes once the measurements of total event rate from three appropriate targets become available. In this way it is thus possible to extract the maximum information on the supersymmetric parameter space obtainable from direct detection experiments, in the case that the dark matter particle is the lightest neutralino. Our scheme is based on suitably normalized forms of the isospin momentum dependent structure functions entering in the spin-dependent elastic neutralino-nucleus cross section. We compare these functions with the commonly used ones and discuss their advantages: in particular, these allow in the spin-dependent cross section to factorize the particle physics degrees of freedom from the momentum transfer dependent nuclear structure functions as it happens in the spin-independent cross section with the nuclear form factor.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗