Search results for "Delta"
showing 10 items of 471 documents
Meson exchange currents in theHe3(γ,π+)3H reaction
1996
We generate meson exchange currents mechanisms for the (\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{+}$) reaction in nuclei starting from the \ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}N amplitude on one nucleon and allowing one of the pions to be produced off shell and be absorbed by a second nucleon. Detailed calculations are presented for the \ensuremath{\gamma} $^{3}\mathrm{\ensuremath{\pi}}^{+3}$H reaction, where we show that the cross section at large momentum transfers is dominated by these mechanisms, helping improve the agreement with experimental data. It is also shown that the meson exchange currents produce important effects in the photon a…
Neutrino Induced Charged Current 1$\pi^+$ Production At Intermediate Energies
2006
The charged current one pion production induced by $\nu_\mu$ from nucleons and nuclei like $^{12}$C and $^{16}$O nuclei has been studied. The calculations have been done for the incoherent and the coherent processes from nuclear targets assuming the $\Delta$ dominance model and take into account the effect of Pauli blocking, Fermi motion of the nucleon and renormalization of $\Delta$ properties in a nuclear medium. The effect of final state interactions of pions has been taken into account. The theoretical uncertainty in the total cross sections due to various parameterizations of the weak transition form factors used in literature has been studied. The numerical results for the total cross…
The isospin structure of photoproduction of πη pairs from the nucleon in the threshold region
2015
Abstract Photoproduction of πη-pairs from nucleons has been investigated from threshold up to incident photon energies of ≈ 1.4 GeV. The quasi-free reactions γ p → p π 0 η , γ n → n π 0 η , γ p → n π + η , and γ n → p π − η were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the γ p → n π + η reaction was measured for the first time). For the π 0 η final state coherent production via the γ d → d π 0 η reaction was also investigated. The experiments were performed at the …
Virtual versus real nuclear Compton scattering in the Delta(1232) region
1996
[EN] In this paper we calculate the cross section for Virtual Compton Scattering off nuclei in the delta resonance region. We also calculate the background for the process from Coherent Bremsstrahlung in nuclei and explore the regions where the Virtual Compton Scattering cross section dominates. The study also shows that it is possible to extract the cross section for Real Compton Scattering from the Virtual Compton one in a wide range of scattering angles.
First measurement of the circular beam asymmetry in the γ→p→π0ηp reaction
2010
Abstract The circular photon asymmetry for π 0 η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.
Baryon transition form factors at the pole
2016
Electromagnetic resonance properties are uniquely defined at the pole and do not depend on the separation of the resonance from background or the decay channel. Photon-nucleon branching ratios are nowadays often quoted at the pole, and we generalize the considerations to the case of virtual photons. We derive and compare relations for nucleon to baryon transition form factors both for the Breit-Wigner and the pole positions. Using the MAID2007 and SAID SM08 partial wave analyses of pion electroproduction data, we compare the $G_M$, $G_E$, and $G_C$ form factors for the $\Delta(1232)$ resonance excitation at the Breit-Wigner resonance and pole positions up to $Q^2=5$ GeV$^2$. We also explore…
Differential cross sections for coherent and incoherent neutral-pion photoproduction from calcium
1989
Differential and absolute cross sections for the coherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\ensuremath{\pi}}^{0}$${)}^{40}$Ca g.s., as well as for the incoherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{0}$${)}^{40}$Ca(g.s.), have been measured with monochromatic photons in the threshold region (${E}_{\ensuremath{\gamma}}$=157--169 MeV). The differential cross section for the coherent process exhibits a diffraction minimum due to the nuclear mass form factor while the incoherent cross section is rather structureless. The cross sections are in good agreement with recent distorted-wave impulse-approximation calculations.
QCD corrections to inclusive ΔS = 1, 2 transitions at the next-to-leading order
1994
24 páginas, 3 figuras, 2 tablas.-- arXiv:hep-ph/9402363v1
Kinetics of growth process controlled by convective fluctuations
2001
A model of the spherical (compact) growth process controlled by a fluctuating local convective velocity field of the fluid particles is introduced. It is assumed that the particle velocity fluctuations are purely noisy, Gaussian, of zero mean, and of various correlations: Dirac delta, exponential, and algebraic (power law). It is shown that for a large class of the velocity fluctuations, the long-time asymptotics of the growth kinetics is universal (i.e., it does not depend on the details of the statistics of fluctuations) and displays the power-law time dependence with the classical exponent $1/2$ resembling the diffusion limited growth. For very slow decay of algebraic correlations of flu…
Verhulst model with Lévy white noise excitation
2008
The transient dynamics of the Verhulst model perturbed by arbitrary non-Gaussian white noise is investigated. Based on the infinitely divisible distribution of the Levy process we study the nonlinear relaxation of the population density for three cases of white non-Gaussian noise: (i) shot noise, (ii) noise with a probability density of increments expressed in terms of Gamma function, and (iii) Cauchy stable noise. We obtain exact results for the probability distribution of the population density in all cases, and for Cauchy stable noise the exact expression of the nonlinear relaxation time is derived. Moreover starting from an initial delta function distribution, we find a transition induc…