Nucleon Isobar Production in Proton-Proton Collisions between 3 and 7GeVc

Abstract

A systematic study has been made of the reactions $\mathrm{pp}\to \mathrm{pp}$ and $\mathrm{pp}\to p{N}^{*}$ in the angular range from ${\theta }_{\mathrm{lab}}={10}^{\circ }$ to ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}={90}^{\circ }$ at 3, 4, 5, 6, and 7 $\frac{\mathrm{GeV}}{c}$. An orthogonal dispersion magnetic spectrometer detected protons from interactions in hydrogen with momentum transfer ($-t$) in excess of 0.5 ${\mathrm{}\left(\mathrm{GeV}\right)\mathrm{}}^2$. Well-defined peaks in the missing-mass spectra occurred at average $N^{*}$ masses of 1240±6, 1508±2, and 1683±3 MeV with average full widths of 102±4, 92±3, and 110±4 MeV, respectively. Below 2400 MeV no other significant enhancements were found. The $N^{*}$ production cross sections $\frac{d\sigma }{\mathrm{dt}}$ near ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}={90}^{\circ }$ are in qualitative agreement with the predictions of the statistical model. For each isobar the differential cross section at fixed energy varies as $\exp (-\frac{v}{v_0})$, where $v\equiv [-\frac{\mathrm{tu}}{\mathrm{}(t+u)\mathrm{}}]$; $v_0$ varies systematically with energy and tends toward the same value ($\approx 0.4$ Ge${\mathrm{V}}^2$) for each isobar at the upper limit of our energy range.