Total Cross Section of Hydrogen for 150- to 750-Mev Positive and Negative Pions

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Abstract

The total cross section of hydrogen for positive and negative pions of 150-750 Mev has been determined.An early preliminary survey using polyethylene-carbon differences is reported and indicated a resonance in the state of isotopic spin and angular momentum equal to $\frac{3}{2}$ (i.e., $T=J=\frac{3}{2}$).A more recent precision determination (\ensuremath{\sim}3-5%) of the total hydrogen cross section for positive pions in the presumed resonance region (140-340 Mev) has been performed using liquid hydrogen transmission measurements.A theoretical analysis of the results in conjunction with other available data strongly supports the hypothesis of a resonance.The behavior of the phase shift of the $T=J=\frac{3}{2}$ state is deduced and given. The most probable solution for the phase shift in this state is found to pass through 90\ifmmode^\circ\else\textdegree\fi{} at \ensuremath{\sim}175-180 Mev, although one cannot rule out the possibility of the resonance (90\ifmmode^\circ\else\textdegree\fi{} phase shift) occurring up to 200 Mev.The $T=\frac{1}{2}$ state cross section is found to be zero within the errors in the resonance region and to become appreciable only above 300 Mev.The present experimental data and other relevant work are analyzed in terms of the recent Chew-Low theory and the Brueckner phenomenological resonance theory and is found to fit the general behavior predicted by both, which incidentally is shown to be of similar form.

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