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Register a new userTheoretical study of the $Delta^{++}-Delta^-$ configuration in the deuteron using antiproton beam
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We study the manifestation of the $Delta^{++}-Delta^-$ component of the deuteron wave function in the exclusive reaction $bar p d to pi^- pi^- Delta^{++}$. Due to the large binding energy the internal motion in the $Delta-Delta$ system is relativistic. We take this into account within the light-cone (LC) wave function formalism and, indeed, found large differences between calculations based on the LC and non-relativistic (NR) wave functions. We demonstrate, that the consistent LC treatment of the $Delta-Delta$ system plays the key role in the separation of the signal and background. Within the LC approach, the characteristic shape of the momentum distribution of the $Delta-Delta$ bound system predicted by the meson-exchange model is well visible on the background of usual annihilations at beam momenta between 10 and 15 GeV/c.
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We discuss the pole mass and the width of the $Delta(1232)$ resonance to third order in chiral effective field theory. In our calculation we choose the complex-mass renormalization scheme (CMS) and show that the CMS provides a consistent power-counting scheme. In terms of the pion-mass dependence, we compare the convergence behavior of the CMS with the small-scale expansion (SSE).
Mechanisms of the charge exchange reaction $dpto {pp}_{!s} Npi$, where ${pp}_{!s}$ is a two-proton system at low excitation energy, are studied at beam energies 1 -- 2 GeV and for invariant masses $M_X$ of the final $Npi $ system that correspond to the formation of the $Delta(1232)$ isobar. The direct mechanism, where the initial proton is excited into the $Delta(1232)$, dominates and explains the existing data on the unpolarized differential cross section and spherical tensor analyzing power $T_{22}$ for $M_X> 1.2$ GeV/$c^2$. However, this model fails to describe $T_{20}.
For the first time, the total yield and inclusive spectra of the $Delta^{++}(1232)$isobar are measured in $ u p$ and $ u n$ charged-current interactions. An indication is obtained that the $Delta^{++}(1232)$ production mainly results from the neutrino scattering on the valence d- quark of the target nucleon. The total yield of $Delta^{++}(1232)$ in $ u p$ interactions is compatible with that measured in hadronic interactions of the same net charge and net baryonic number. The yield of $Delta^{++}(1232)$ in $ u n$ interactions is significantly suppressed as compared to the case of the proton target. The form of the squared transverse momentum distributions, both in $ u p$ and $ u n$ interactions, is found to be compatible with the available data on the neutrinoproduction of $Lambda$ hyperon. The experimental data are compared with the LEPTO6.5 model predictions.
To determine nonspherical angular momentum amplitudes in hadrons at long ranges (low Q^2), data were taken for the p(vec{e},ep)pi^0 reaction in the Delta region at Q^2=0.060 (GeV/c)^2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W=1232 MeV are: M_{1+}^{3/2} = (40.33 +/- 0.63_{stat+syst} +/- 0.61_{model}) (10^{-3}/m_{pi^+}),Re(E_{1+}^{3/2}/M_{1+}^{3/2}) = (-2.28 +/- 0.29_{stat+syst} +/- 0.20_{model})%, and Re(S_{1+}^{3/2}/M_{1+}^{3/2}) = (-4.81 +/- 0.27_{stat+syst} +/- 0.26_{model})%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with non-linear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q^2 variation, of the pionic contribution at large distances.
We report a measurement of the $pi^-$ photoproduction beam asymmetry for the reaction $vec{gamma} p rightarrow pi^- Delta^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $Sigma$ is measured as a function of four-momentum transfer $t$ to the $Delta^{++}$ and compared to phenomenological models. We find that $Sigma$ varies as a function of $t$: negative at smaller values and positive at higher values of $|t|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.
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