Study of the reactionp↑p→pπ+n with polarized beam from 1.18 to 1.98 GeV/c

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Abstract

We present density-matrix elements and single-spin correlations for the reaction ${p}_{\ensuremath{\uparrow}}$p\ensuremath{\rightarrow}p${\ensuremath{\pi}}^{+}$n at 1.18, 1.47, 1.71, and 1.98 GeV/c, using both longitudinal and transverse beam polarizations. For the ${p}_{\ensuremath{\uparrow}}$p\ensuremath{\rightarrow}${\ensuremath{\Delta}}^{++}$n subprocess we find quite different energy dependence for the helicity-(1/2) and helicity-(3/2) ${\ensuremath{\Delta}}^{++}$-production asymmetries. The helicity-(1/2) asymmetry has ${p}_{\mathrm{lab}}$ dependence similar to the polarization in ${p}_{\ensuremath{\uparrow}}$p\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$d, while the helicity-(3/2) asymmetry changes sign between 1.18 and 1.47 GeV/c. By fitting the production angle dependence of the spin correlations, we obtain joint moments which are easily related to the partial-wave structure. We have carried out a partial-wave analysis with the moments data. We find that the production wave intensities are qualitatively consistent with the elastic phase-shift analyses, and the phases vary smoothly with ${p}_{\mathrm{lab}}$. From the absence of Breit-Wigner phase behavior, we conclude that the dinucleon resonances seen in the pp elastic waves are not true coupled-channel Briet-Wigner states in NN and N\ensuremath{\Delta}.

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