Electromagnetic Widths Research Articles

Application of the Oscillation Symmetry to the Electromagnetic Interactions of Some Particles, Nuclei, and Atoms

The oscillation symmetry is first applied to electromagnetic interactions of particles and nuclei. It is shown that the differences between successive masses plotted versus their mean values and the electromagnetic decay widths Γee of 0^−(1^−−) b¯b and c¯c mesons, plotted versus their masses, agree with such symmetry. Then it is shown that the variation of the energy differences between different levels of several nuclei from 8Be to 20Ne, corresponding to given electric or magnetic transitions, display also oscillating behaviours. The electromagnetic widths of the electric and magnetic transitions between excited levels of these nuclei, plotted versus the corresponding differences between energies agree also with this property. The oscillating periods describe also an oscillation, the same for E1, M1, and E2 transitions. It is also the case for the multiplicative factor used β, and for ratios between these parameters. The oscillation symmetry is then applied to atomic energy levels of several neutral atoms from hydrogen to phosphorus. The data exhibit nice oscillations when plotted in the same way as before. The oscillations in various nuclear and atomic periods of different elements (A) exhibit the same shape and can be fitted by the same distribution.

Charmonium description from a generalized screened potential model

A generalized screened potential model (GSPM), recently developed to study the bottomonium spectrum, is applied to the calculation of charmonium masses and electromagnetic widths. The presence in the GSPM of more quark-antiquark bound states than in conventional non screened potential models, allows for the assignment of GSPM states to cataloged non conventional $J^{++}$ charmonium resonances as well as for the prediction of new (non cataloged) $J^{++}$ states. The results obtained seem to indicate that a reasonable overall description of $J^{++}$ charmonium resonances is feasible.

New insights into the spin structure of the nucleon

We analyze the low-energy spin structure of the nucleon in a covariant effective field theory with explicit spin-3/2 degrees of freedom to third order in the small scale expansion. Using the available data on the strong and electromagnetic width of the Delta-resonance, we give parameter-free predictions for various spin-polarizabilities and moments of spin structure functions. We find an improved description of the nucleon spin structure at finite photon virtualities for some observables and point out the necessity of a fourth order calculation.

Hyperfine mixing in electromagnetic decay of doubly heavy bc baryons

We investigate the role of hyperfine mixing in the electromagnetic decay of ground state doubly heavy bc baryons. As in the case of a previous calculation on b→c semileptonic decays of doubly heavy baryons, we find large corrections to the electromagnetic decay widths due to this mixing. Contrary to the weak case just mentioned, we find here that one cannot use electromagnetic width relations obtained in the infinite heavy quark mass limit to experimentally extract information on the admixtures in a model independent way.

What can we learn about baryon-baryon interaction from hypernuclei Λ 6 H and Λ 8 H?

At the LHE JINR, an original approach to hypernuclear experiments was elaborated to produce relativistic hypernuclei. The production cross sections and lifetimes, τ, of Λ 3 H and Λ 4 H were measured successfully. The results of recent experiments on 5H and 7H nuclei suggest that the hypernucleus Λ 6 H might be stable and that this may be the case even for Λ 8 H. The unique quality of the spectrometer SPHERE may be used to identify unambiguously the isotopes of hyperhydrogen—through their pionic decay Λ H → π − + A He—including the new hypernuclei Λ 6 H and Λ 8 H with extreme values of N/Z of 4 and 6, respectively. The confirmation of the very existence of these neutron-rich hypernuclei would be a strong motivation to search for their spectra in strangeness and double-charge-exchange reactions (K stop − , π +) at FINUDA or (π −, K +) at J-PARC. It is very probable that, similarly as in Λ 4 H, there is a low-lying state 1+ also in Λ 6 H and Λ 8 H. If their electromagnetic width (M1) is small enough, we could see two different values of τ for Λ 6 H and/or Λ 8 H. We investigate the spacings of the 1+ and 0+ states of Λ 4 H, Λ 6 H, and Λ 8 H. The understanding of the structure of isospin asymmetric systems plays a key role in the description of systems as diverse as neutron-rich nuclei and neutron matter.

Addendum: Attenuation of the intensity within a superdeformed band

We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for the decay-out of a superdeformed band as a function of the parameters: $\Gamma^\downarrow/\Gamma_S$, $\Gamma_N/D$, $\Gamma_S/D$ and $\Delta/D$. Here $\Gamma^\downarrow$ is the spreading width for the mixing of an SD state $|0>$ with a normally deformed (ND) doorway state $|d>$, $\Gamma_S$ and $\Gamma_N$ are the electromagnetic widths of the the SD and ND states respectively, $D$ is the mean level spacing of the compound ND states and $\Delta$ is the energy difference between $|0>$ and $|d>$. The maximum possible effect of an order-chaos transition is inferred from analytical and numerical calculations of the decay intensity in the limiting cases for which the ND states obey Poisson and GOE statistics. Our results show that the sharp attenuation of the decay intensity cannot be explained solely by an order-chaos transition.

A model for the decay out of superdeformed bands

The decay out of superdeformed, rotational bands is studied in terms of the spreading of the superdeformed strength on states corresponding to normal configurations. The mixing of the superdeformed state depends on the tunneling through the potential energy barrier separating the two shapes. Simple, yet accurate estimates of the decay probability are presented in terms of the transmission coefficient of the barrier, and the electromagnetic width and level density of the normal states.

Electromagnetic width of the sigma meson from the sigma model.

We calculate the decay width of the \ensuremath{\sigma} (or \ensuremath{\epsilon}) scalar meson into two photons, in the framework of the linear \ensuremath{\sigma} model. We are motivated in part by a recent experimental determination from photon-photon annihilation into pion pairs, which suggested a surprisingly large value. We argue that the model takes into account a plausible hybrid structure of the scalar mesons, as having fermion-antifermion as well as boson pair constituents. We show that the corresponding two contributions tend to cancel, leading, on the contrary, to a rather small width.

Low-lying isoscalar dipole excitations in 208Pb

Inelastic excitations have been studied in 48 MeV α-scattering from 208Pb. A concentration of isoscalar L = 1 strength is observed at E x ≈ 5.5 Mev which is interpreted as a dipole excitation mode representing a dipole oscillation of the nuclear diffuseness. A consistent description of inelastic excitations and electromagnetic widths is obtained.

KS0*and its uses

We point out that Primakoff conversion of ${K}_{L}^{0}$'s produces ${K}_{S}^{{0}^{*}}$'s. This makes possible a practical tagged ${K}_{S}^{0}$ beam. In addition one can test the recent suggestion that $I=1$ exchange effects necessitate large corrections to Primakoff measurements of vector-meson electromagnetic widths. It will also be possible to measure $\ensuremath{\Gamma}({K}^{{0}^{*}}\ensuremath{\rightarrow}{K}^{0}\ensuremath{\gamma})$ in a manner independent of the alleged corrections.

Hadronic and electromagnetic widths of mesons in the style schemes

Hadronic and electromagnetic transitions between meson states are studied in the Sp(8) and SO(8) schemes. The case where an extra quark is at low mass is compared and contrasted with the more conventional radial excitation picture.

Isobar Analysis ofγp→ηp

An analysis of the available data below 2.24-GeV c.m. energy for the process $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ yields values of $G\ensuremath{\equiv}\ensuremath{\Gamma}(R\ensuremath{\rightarrow}\ensuremath{\gamma}p)\ensuremath{\Gamma}(R\ensuremath{\rightarrow}\ensuremath{\eta}p)$ for several $s$-channel resonances, $R$. By varying the details of the direct-channel isobar model it is found that the values of $G$ are reasonably model-independent. When these values are combined with information from other reactions it is possible to calculate electromagnetic widths for the important resonance states in this process. These include essential contributions from ${S}_{11}$ and ${P}_{11}$ states; in addition, admixtures of ${P}_{13}$, ${D}_{13}$, ${F}_{17}$, and ${G}_{17}$ resonances are also needed in order to obtain a good fit to the data. An excellent fit is found by including some recently conjectured stray baryonic states which do not couple significantly to the $\ensuremath{\pi}N$ channel.

Electroproduction of nucleon isobars in the quark model

The electroproduction of N ∗ resonances in the quark model has been extensively studied by Thronber, using the symmetric harmonic oscillator quark model, developed later by Faiman and Hendry. Encouraging results were obtained for small q 2, but there was a strong disagreement for q 2 ⩾ 1 GeV 2 not only for the absolute values but also for the ratio dσ dω ( N ∗) dσ dω ( elastic) . We show that this disagreement is mainly due to a bad choice of the frame where the non-relativistic transition form factors are calculated. There are physical reasons for choosing a frame near the Breit frame. We also introduce the quark form factor needed by the various other successes of the symmetric oscillator quark model (spectroscopy, strong and electromagnetic widths, differential photoproduction, elastic and diffractive processes), while Thornber considered point quarks. We discuss the origin of this quark form factor, either static charge distribution or mediating particle. Without any free parameter, we obtain good results for the ratio dσ dω ( N ∗) dσ dω ( elastic) up to large q 2 (∼ 3 GeV 2) for the four main bumps. However, when we discuss the contributions of all the established resonances ( M < 2.2 GeV) there arise problems with the radial excitations and the P 13(1870). Concerning the absolute magnitude, we think we may attribute the discrepancy between the dipole and gaussian form factors to relativistic corrections as first suggested by Licht and Pagnamenta, and Fujimura et al.

Spins and Widths of Energy Levels in the 5-9-MeV Region

Neutron-capture $\ensuremath{\gamma}$ rays from the Texas A research reactor have been used to excite one nuclear energy level each in $^{90}\mathrm{Zr}$, Cd, Sn, Hg, $^{205}\mathrm{Tl}$, and $^{208}\mathrm{Pb}$, and two in $^{209}\mathrm{Bi}$, in the 5-9-MeV region. Angular-distribution measurements of the scattered $\ensuremath{\gamma}$ rays showed that the transitions were all consistent with dipole radiation. However, for various reasons, the data could also be reproduced in most cases by assuming a mixture of dipole and quadrupole radiation. Three further measurements were made for the $^{90}\mathrm{Zr}$, the $^{205}\mathrm{Tl}$, the $^{208}\mathrm{Pb}$, and one $^{209}\mathrm{Bi}$ excitation: (1) an absolute differential cross-section measurement on the resonance scattering, (2) a resonance absorption measurement, and (3) a differential cross-section measurement at liquid-nitrogen temperature. From these data, values were found for ${\ensuremath{\Gamma}}_{0}$ (the excited level width for an electromagnetic transition to the ground state), $\ensuremath{\Gamma}$ (the excited level total electromagnetic width), and $\ensuremath{\epsilon}$ (the energy displacement between the neutron-capture $\ensuremath{\gamma}$-ray energy and the resonance energy). The values of ${\ensuremath{\Gamma}}_{0}$ (between 0.14 and 1.0 eV) were found to be about 10 times larger than the values usually found for $\ensuremath{\gamma}$-ray widths in this energy region as determined from neutron-capture reactions.

Ground state electromagnetic widths of the 6.32 MeV level in 15N

Inelastic scattering of 50, 53 and 57 MeV electrons has been used to determined Γ γ 0(M1) = 3.4 ± 0.7 Ev and Γ γ 0(E2) = 0.06 ± 0.02 eV for the 6.32 MeV level in 15N.

Superconvergence sum rules for radiative decays of meson resonances

We consider the process γπ→ρп for which three sum rules are derived from high-energy behaviour hypothesis. Combining these sum rules with the analogous ones for the process ρπ→ρπ we determine the electromagnetic widths of the ω, A1, A2 resonances, and theS-wave/D-wave ratio for the A1→ρπ decay. We discuss some features of gauge invariance and superconvergence requirements: in particular, we derive some already known low-energy theorem consequences,e.g. the sum rule obtained byHarari for Compton scattering. This last one and the Cabibbo and Radicati sum rule are used to select the best values of the ω, A1, A2 electromagnetic widths.

Electromagnetic Properties of the Low-Lying States ofC6126in the Oscillating Drop Model

The electromagnetic properties of the first four states of $_{6}\mathrm{C}_{6}^{12}$ are discussed within the framework of the incompressible liquid-drop model. The radius of the drop is determined by the elastic electron scattering from the ground state. The surface tension and mass participating in the motion are treated as parameters and are fixed by the energy and lifetime of the first-excited state (${2}^{+}$) at 4.43 Mev. This yields an inelastic-electron scattering cross section close to the experimental result. The ${0}^{+}$ state at 7.66 Mev is then identified with the two-surfon state and the inelastic electron scattering cross section and matrix element for pair emission to the ground state are found to be in quantitative agreement with the experimental results. The state at 9.63 Mev is studied as both the ${2}^{+}$, two-surfon state and ${3}^{\ensuremath{-}}$, one-surfon state which is also predicted at this energy, and it is shown that only the ${3}^{\ensuremath{-}}$ state has an inelastic electron-scattering cross section which is consistent with the experimental results. This total electromagnetic width of the ${0}^{+}$ state at 7.66 Mev, which is astrophysical interest, is calculated to be ${\ensuremath{\Gamma}}_{\mathrm{el}}=1.02\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ ev. The other electromagnetic widths for the first four states are calculated and reasonable agreement is obtained with the experimental data where it exists. The other members of the ${0}^{+}$, ${2}^{+}$, ${4}^{+}$ triplet are unassigned. There are other levels in the vicinity of 10 Mev in ${\mathrm{C}}^{12}$. It would be of interest to know what their spins are.