相关论文: e+e- pair production from nucleon targets in the r…
We discuss two processes, the $\pi N \to e^+e^- N$ and the $\gamma N \to e^+e^- N$ reactions, below and close to the vector meson production threshold ($1.40<\sqrt s <1.75$ GeV). The aim is to gain understanding of the coupling of vector…
The $\pi^-p \to e^+e^- n$ and $\pi^+n \to e^+e^- p$ reaction cross sections are calculated below and in the vicinity of the vector meson ($\rho^0$, $\omega$) production threshold. These processes are largely responsible for the emission of…
The study of the $\pi N\to \rho^0 N$ and $\pi N \to \omega N$ amplitudes below and close to the vector meson production threshold ($1.4<\sqrt s <1.8$ GeV)reveals a rich structure arising from the presence of baryon resonances in this energy…
The study of the pi^- p -> rho^0 n and pi^- p -> omega n amplitudes close and below the vector meson production threshold (1.2< sqrt(s) <1.8 GeV) reveals a rich dynamics arising from the presence of specific baryon resonances in this energy…
The exclusive photoproduction of $e^+e^-$ pairs from nucleons close to the vector meson production threshold ($1.4<\sqrt s <1.8$ GeV) results from two main processes: the emission of Bethe-Heitler pairs and the photoproduction of $\rho^0$-…
We present a dynamical study of $e^+e^-$ production in $\pi^-$A reactions at 1.3 and 1.7 GeV on the basis of the Coupled-Channel-BUU approach. The contributions from vector mesons ($\rho,\omega$) are calculated taking into account the…
The reaction $\pi^{-}p \to \eta n$ is investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region. The meson baryon channels included are $\pi N$, $\eta N$, $\pi \Delta$, $\sigma N$,…
We present a study of the reaction $\pi^-p \to ne^+e^-$ for $\sqrt{s}=1.49\,\textrm{GeV}$, including non-resonant Born terms and contributions of the $N(1440)$, $N(1520)$, $N(1535)$ resonances ($R$), using an effective-Lagrangian model,…
Dielectron production in reactions $\pi^- p \rightarrow n e^+e^-$ and $\pi^- p \rightarrow n e^+e^- \gamma$ at energies less than 1 GeV is studied assuming electron-positron pair production to occur in the virtual time-like photon splitting…
The process $e^+e^- \to \pi^0\gamma$ has been studied in the experiment with the SND detector at the VEPP-2M $e^+e^-$ collider. The $e^+e^- \to \pi^0\gamma$ cross section has been measured in the center-of-mass energy range from 0.60 to…
The ep -> e'pi^+n reaction was studied in the first and second nucleon resonance regions in the 0.25 GeV^2 < Q^2 < 0.65 GeV^2 range using the CLAS detector at Thomas Jefferson National Accelerator Facility. For the first time the absolute…
The production of the light vector mesons $V = \rho, \omega, \phi$ in the reactions $\pi N \to V N$ and $N N \to V N N$ near threshold is studied. The subsequent electromagnetic decay $V \to \gamma^* \to e^+ e^-$ is particularly suited for…
The process $e^+e^-\to \pi^+\pi^-\pi^0\gamma$ is studied at a center-of-mass energy near the $\Upsilon(4S)$ resonance using a data sample of 469 fb$^{-1}$ collected with the BABAR detector at the PEP-II collider. We have performed a precise…
It is shown that most of the models for analyzing meson-baryon reactions in the nucleon resonance region can be derived from a Hamiltonian formulation of the problem. An extension of the coupled-channel approach to include $\pi\pi N$…
At very high energies, pair production ($\gamma\to e^+e^-$) exhibits many interesting features. The momentum transfer from the target is very small, so the reaction probes the macroscopic properties of the target, rather than individual…
We present a model of electron-positron pair production in pion-nucleon collisions in the exclusive reaction \pi N -> Ne^+e^-. The model is based on an effective field theory approach, incorporating 16 baryon resonances below 2 GeV.…
The process e^+e^-\to\pi^0\gamma in the energy range \sqrt{s}=0.60-1.06 GeV was studied at VEPP-2M collider with SND detector using 14 pb^{-1} of integrated luminosity. Data were analyzed in the framework of the vector meson dominance…
The isoscalar-isovector ($\rho-\omega$) interferences in the exclusive reactions $\pi^- p \to n e^+ e^-$ and $\pi^+ n \to p e^+ e^-$ near the $\omega$ threshold leads to a distinct difference of the dielectron invariant mass distributions…
The nucleon resonances are investigated within a dynamical coupled-channels model of pi N and gamma N reactions up to the invariant mass W = 2 GeV. The meson-baryon (MB) channels included in the calculations are MB = pi N, eta N, K Lambda,…
We discuss ${\gamma}{\gamma}\to {\pi}{\pi}$ reactions, starting from the two-pion threshold up to about $\sqrt{s_{{\gamma}{\gamma}}}$ = 6 GeV. We include the dipion continuum due to pion exchange (for ${\pi}^+{\pi}^-$) and ${\rho}^\pm$…