Nonresonant Channels Research Articles

Search forB0→J/ψD¯0andB+→J/ψD¯0π+decays

We report the results of a search for the decay modes B0 -> J/psi D0bar and B+ -> J/psi D0bar pi+. The analysis is based on 140 $\rm fb^{-1}$ of data accumulated by the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. No significant signals are observed and we determine the branching fraction upper limits B(B0 -> J/psi D0bar) < 2.0 10^{-5} and B(B+ -> J/psi D0bar pi+) < 2.5 10^{-5} at 90% confidence level. These results rule out the explanation of the excess in the low momentum region of the inclusive J/psi spectrum as intrinsic charm content in the B meson. The branching fractions of the corresponding non-resonant decay channels are also reported.

Photon-assisted Fano resonance and corresponding shot noise in a quantum dot

We have studied the Fano resonance in photon-assisted transport in a quantum dot and calculated both the coherent current and spectral density of shot noise. It is predicted, for the first time, that the shape of Fano profile will also appear in satellite peaks. It is found that the variations of Fano profiles with the strengths of nonresonant transmissions are not synchronous in absorption and emission sidebands. The effect of interference on photon-assisted pumped current has been also investigated. We further predict the current and spectral density of shot noise as a function of the phase, which exhibits an intrinsic property of resonant and nonresonant channels in the structures.

Excitation modes of11LiatEx∼1.3MeVfrom proton collisions

The cross section for $p{\ensuremath{-}}^{11}\mathrm{Li}$ inelastic scattering at 68 MeV/nucleon is evaluated using the multiple scattering expansion of the total transition amplitude (MST) formalism, and compared with the breakup in the shakeoff approximation. Three different potential models for ${}^{11}\mathrm{Li}$ are used to calculate the ${}^{11}\mathrm{Li}{(p,p}^{\ensuremath{'}})$ continuum excitations, and all show peaks below 3 MeV of excitation energy, both in resonant and some nonresonant channels. In the most realistic model of ${}^{11}\mathrm{Li},$ there is a strong dipole contribution associated with attractive but not a fully-fledged resonant phase shifts, and some evidence for a ${J}_{\mathrm{nn}}^{\ensuremath{\pi}}{=0}_{2}^{+}$ resonant contribution. These together form a pronounced peak at around 1--2 MeV excitation, in agreement with experiment, and this supports the use of the MST as an adequate formalism to study excited modes of two-neutron nuclear halos.

Raman scattering through a metal-insulator transition

The exact solution for nonresonant A1g and B1g Raman scattering is presented for the simplest model that has a correlated metal-insulator transition--the Falicov-Kimball model, by employing dynamical mean field theory. In the general case, the A1g response includes nonresonant, resonant, and mixed contributions, the B1g response includes nonresonant and resonant contributions (we prove the Shastry-Shraiman relation for the nonresonant B1g response) while the B2g response is purely resonant. Three main features are seen in the nonresonant B1g channel: (i) the rapid appearance of low-energy spectral weight at the expense of higher-energy weight; (b) the frequency range for this low-energy spectral weight is much larger than the onset temperature, where the response first appears; and (iii) the occurrence of an isosbestic point, which is a characteristic frequency where the Raman response is independent of temperature for low temperatures. Vertex corrections renormalize away all of these anomalous features in the nonresonant A1g channel. The calculated results compare favorably to the Raman response of a number of correlated systems on the insulating side of the quantum-critical point (ranging from Kondo insulators, to mixed-valence materials, to underdoped high-temperature superconductors). We also show why the nonresonant B1g Raman response is ``universal'' on the insulating side of the metal-insulator transition.

Production of a0 +-mesons in the reaction pp↦da0 +

We investigate the reaction pp↦da0+ at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a0+ is considered as a usual u\(\) quark model state with two decay channels a0+↦K+\(\) and a0+↦π+η. Calculated cross-sections for a0+ production as well as for the corresponding non-resonant channels pp↦dK+\(\) and pp↦dπ+η are compared. Especially, in case of the final channel dπ+η, high statistics measurements are necessary to extract the a0+ signal from the high non-resonant background.

New analysis of the radiative decayω→ηγin proton-antiproton annihilation at rest

We report on a measurement of the branching ratio of the rare decay ω→ηγ relative to the well known decay ω→π0γ. The ω’s are produced in pp¯→ηω and pp¯→π0ω. Eigenstate mixing and interference effects of the ω and ρ0 are taken into account, as well as coherent interference with the background. We find evidence for the non-resonant annihilation channel B(pp¯→ηηγ)=(3.5±1.3)×10−5 and limit the value of B(ω→ηγ) to the range of (0.7to5.5)×10−4 depending on the degree of coherence with the background.Received 4 June 1999DOI:https://doi.org/10.1103/PhysRevD.61.032002©2000 American Physical Society

Nonresonant semileptonic heavy quark decay

In both the large N_c limit and the valence quark model, semileptonic decays are dominated by resonant final states. Using Bjorken's sum rule in an "unquenched" version of the quark model, I demonstrate that in the heavy quark limit nonresonant final states should also be produced at a significant rate. By calculating the individual strengths of a large number of exclusive two-body nonresonant channels, I show that the total rate for such processes is highly fragmented. I also describe some very substantial duality-violating suppression factors which reduce the inclusive nonresonant rate to a few percent of the total semileptonic rate for the finite quark masses of B decay, and comment on the importance of nonresonant decays as testing grounds for very basic ideas on the structure, strength, and significance of the quark-antiquark sea and on quark-hadron duality in QCD.

Theoretical update on two non-resonant three-body channels in charmed meson decays

Predictions of two channels in the three-body decays of the charmed mesons are made within heavy hadron chiral perturbation theory. There still exists the problem that the theoretical expectation is too small compared to experimental data.

Charm nonleptonic decays and final state interactions

A global previous analysis of two-body nonleptonic decays of D mesons has been extended to the decays involving light scalar mesons. The allowance for final state interaction also in nonresonant channels provides a fit of much improved quality and with less symmetry breaking in the axial charges. We give predictions for about 50 decay branching ratios yet to be measured. We also discuss long distance contributions to the difference ΔΓ between the D S and D L widths.

Differential cross sections for the electron-impact excitation of hydrogenlike carbon.

We report on a study of total and differential excitation cross sections for the electron-impact excitation of hydrogenlike carbon for the transitions 1{ital s} {sup 2}{ital S}{r_arrow}2{ital s} {sup 2}{ital S} and 2{ital p} {sup 2}{ital P}. These calculations have been performed for electron-impact energies ranging from 28.2 to 29.5 Ry using the close-coupling {ital R}-matrix method. This energy region has been chosen because in addition to the direct excitation of 2{ital s} and 2{ital p}, there is a sizable contribution to the excitation cross section from the doubly excited two-electron states (3{ital l}3{ital l}{prime}), which decay predominantly to {ital n}=2 via autoionization. Differential cross sections for both the direct nonresonant channel and in the vicinity of several autoionizing resonant states are presented. The differential cross sections in the vicinity of the autoionizing resonant states are shown to be very rich in structure. We discuss the relevance of these calculations to a recent experiment that measured the electron emission spectra for the collision of C{sup 5+}+H{sub 2}.

N2+ (A 2Piu from X 2Sigmag+) excitation in the charge-exchange collision with caesium: two-electron effects at keV energies

Charge-exchange collisions of 5 keV N2+ on Cs are examined using translational spectroscopy to identify the internal energy states of the fast neutralized products. Optical pumping of the reactant, N2+(A from X) or Cs(2P from 2S), is used to change selectively the electronic configurations and the reaction energy defect, while monitoring the resulting changes in the product state distribution. The N2+/Cs charge exchange yields N2 Rydberg states. A simple model of their formation would involve the transfer of the single outer electron in Cs into a Rydberg orbit built on the N2+ core. However, the present studies identify a surprising and highly efficient reaction mechanism in which the electronic configuration of the N2+ reactant is also changed during the electron transfer. This facile two-electron process, which occurs for both near-resonant and non-resonant reaction channels acid has not been observed in other molecular charge-transfer reactions, is believed to be related to the very small energy separation between the ground and first excited electronic states of N2+.

Resonant and nonresonant multiphoton ionization of helium.

We have investigated the multiphoton ionization of helium at wavelengths between 310 and 330 nm at intensities between 8\ifmmode\times\else\texttimes\fi{}${10}^{13}$ and 5\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$ and at 630 nm at intensities of 1\ifmmode\times\else\texttimes\fi{}${10}^{15}$ W/${\mathrm{cm}}^{2}$. We characterize the ionization processes from photoelectron energy and angular distributions observed concurrently with photoion spectra. At the shorter wavelengths we find that resonant enhancement via the ac Stark shifted six-photon resonant states (1s3d and 1s3s) is a dominant ionization path as described previously by Perry, Sz\oke, and Kulander [Phys. Rev. Lett. 63, 1058 (1989)] and by Rudolph et al. [Phys. Rev. Lett. 66, 3241 (1991)]. At intensities above those required for resonant enhancement, and at wavelengths longer than those required for six-photon resonance, we observe that nonresonant seven-photon ionization dominates. This process gives rise to continuous distributions of low-energy electrons with characteristic angular distributions that peak near 0\ifmmode^\circ\else\textdegree\fi{} and 60\ifmmode^\circ\else\textdegree\fi{} relative to the laser polarization. At yet higher intensities, above the threshold where the nonresonant seven-photon channel closes, the dominant ionization path occurs via seven-photon resonant states with odd parity. This path gives rise to angular distributions characteristic of intermediate states with f character.

Anomalous intensity-dependent vibrational distributions of oxygen molecules in a nonresonant laser field: A molecular perspective.

We report on the results of nonlinear ionization and dissociation of gas-phase oxygen molecules in an intense (${10}^{11\mathrm{\ensuremath{-}}13}$ W/${\mathrm{cm}}^{2}$) laser field. The investigations were performed with the second- and third-harmonic wavelengths of two different laser systems; a 50-ps Nd:YLF (where YLF denotes yttrium lithium fluoride) and a 10-ns Nd:YAG (where YAG represents yttrium aluminum garnet). Measurements include energy resolved photoelectron and mass spectroscopy. We report on an interesting observation made with excitation of the neutral with green (\ensuremath{\sim}2.3 eV) photons, in which the vibrational distribution of the molecular ion shows a strong intensity dependence. We have analyzed this intensity-dependent behavior to be a result of a complex interplay between different resonant and nonresonant electronic channels, which to first approximation does not require dynamical Stark shifting of states. A model is presented that describes this behavior and results in the determination of the molecular constants for the intermediate states.

Comment on "Resonant and nonresonant contributions to the photoactivation of 111Cd"

The most recent investigation of the photoactivation of isomeric nuclei reported by Kr\ifmmode \check{c}\else \v{c}\fi{}mar et al. continues to contain a strong contribution from nonresonant channels. In this Comment we report that integrated cross sections for resonant photoactivation of isomeric levels in $^{87}\mathrm{Sr}$, $^{111}\mathrm{Cd}$, and $^{113,115}\mathrm{In}$ have been calculated from recent nuclear structure data and compared to those experimental results which assert that nonresonant contributions are important. The latter have shown systematically smaller values and the amount of missing resonant strength can be correlated to the magnitude of nonresonant cross section found in these investigations. Monte Carlo simulations of realistic experimental geometries display important components in the photon fields, resulting from environmental Compton scattering, which have been omitted in previous analyses of experimental data. The strength and shape of this contribution as a function of the experimentally important parameters suggest that the data can be explained entirely on the basis of a resonant excitation mechanism without any need to introduce a nonresonant contribution.

Anomalous renormalization of cluster-folding interactions for 6Li-nucleus scattering at low energies

The validity of cluster-folding (CF) interactions for elastic scattering of 6Li by various nuclei is investigated in the α+d+target three-body model. The 6Li→α+d breakup process is taken into account in the framework of the continuum-discretized coupled-channels (CDCC). It is shown that, at low energies below E lab A p ≅10 MeV , the real part of the CF potentials has to be reduced by about (40–50)%, even when the resonant and non-resonant breakup channels are explicitly included in the CDCC calculations, while no renormalization is necessary for fits to scattering at higher energies.

On the γNΔ quadrupole coupling constant(s)

The extraction of the gamma N Delta transverse and longitudinal quadrupole transition form factors gE and gC from the interference measured in (ep, e'p' pi 0) at resonance is discussed. It is shown that the background mechanisms in the non-resonant channels are substantially depressed thus allowing the direct determination of gC and gE. The two quantities, which have to be equal at pseudo-threshold, vary for 0>k2>-0.6 (GeV/c)2 between 0 and -0.1 gM. The necessity of an explicit evaluation of dispersive effects coming from pionic contributions to confirm their four-momentum transfer dependence and their connection with the pseudo-threshold value is stressed.

Vibrationally resolved shape resonant photoionization of N2O

We report a vibrationally resolved dispersed fluorescence study of 7σ−1 shape resonant photoionization in N2O. Previous work indicates that there are two shape resonances in the εσ channel, and our results demonstrate that the lower energy shape resonance (hνexc≊20 eV) results in non-Franck–Condon vibrational branching ratios over a wide range. Moreover, the cross section curves for alternative vibrational modes behave differently, and we show that the symmetric stretch exerts a greater influence on resonance behavior than the asymmetric stretching vibration. Such comparisons of vibrationally resolved partial cross section curves provide qualitative insights into the shape resonant photoionization dynamics for polyatomic targets. The higher energy shape resonance is apparently masked by the presence of the dominant nonresonant επ channel. In addition to information on the photoionization dynamics, these results also provide spectroscopic data on the ionic potential surfaces. Specifically, we obtain ratios of Franck–Condon factors for N2O+ (A→X) transitions which are useful for testing calculated properties of the ion.

Contributions from two-particle scattering to the extraordinary Hall effect in Kondo systems.

The contributions of skew scattering to the extraordinary Hall effect (EHE) in Kondo-type systems have been evaluated by using current-current correlation functions. By using this formalism we take account of two-electron scattering processes that are neglected in the conventional one-electron scattering theory of the EHE. We evaluate the correlation functions for dilute Kondo systems by considering only independent single-site scattering. We find there are two types of contributions to the EHE. Type-I terms come from diagrams in which the energies of the propagators are held fixed. We find that these type-I contributions reproduce the EHE found by the one-electron formalism, i.e., the elastic impurity- or potential-scattering contribution; in addition, there is a spin-scattering contribution which was not previously incorporated in the one-electron scattering formalism. The type-II contributions come from diagrams in which energy is exchanged between resonant and nonresonant scattering channels. These contributions to the EHE are new, i.e., they require two-electron scattering processes, and therefore perforce cannot be accounted for in a one-electron formalism. We find the type-II contributions to the EHE are as large as those of type I at low temperatures T${T}_{0}$, where ${T}_{0}$ is the characteristic energy scale of the single-ion Kondo problem; at high temperatures T\ensuremath{\gg}${T}_{0}$, they are negligible compared with type-I contributions. To obtain the Hall effect we must have scattering in two partial-wave channels whose orbital angular momenta differ by 1\ensuremath{\Elzxh}. To account for the dominant resonant Kondo scattering, we use the Anderson mixing interaction and consider the local electron is in a spin-orbit-coupled j state. In the nonresonant channel we consider two-electron charge- and spin-scattering terms whose origins could be, interalia, the direct and exchange parts of the Coulomb interaction between local and conduction electrons.

Activation of 111Cdm by single pulses of intense bremsstrahlung.

Described here is the use of a calibrated bremsstrahlung source to resolve conflicts in previous studies of the reaction $^{111}\mathrm{Cd}$(\ensuremath{\gamma},\ensuremath{\gamma}'${)}^{111}$${\mathrm{Cd}}^{\mathrm{m}}$ through a level located near 1200 keV. We report an integrated cross section of (9.8\ifmmode\pm\else\textpm\fi{}2.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}29}$ ${\mathrm{cm}}^{2}$ keV with no evidence of any importance of nonresonant channels of excitation.

Activation of 115Inm by single pulses of intense bremsstrahlung.

A new technique has been recently described for the absolute calibration of intense sources of pulsed radiation in the 0.2--1.5 MeV range of photon energies. An activation technique, it depended upon the storage of samples of the irradiating spectrum in the form of populations of nuclei excited to isomeric states with lifetimes of seconds to hours. Described here is the use of such a calibrated source to resolve severe conflicts in previous studies of the reaction /sup 115/In(..gamma..,..gamma..')/sup 115/In/sup m/ through the 1078 keV J/sup ..pi../ = (5/2/sup +/ level; this mode has traditionally served as the archetype for (..gamma..,..gamma..') reactions. We report an integrated cross section of (18.7 +- 2.7) x 10/sup -2/ cm/sup 2/ keV with no evidence of any importance of nonresonant channels of excitation.