The reaction $np\to pp{\pi }^{-}$ from threshold up to 570 MeV

Abstract

The reaction $np\to pp{\pi }^{-}$ has been studied in a kinematically complete measurement with a large acceptance time-of-flight spectrometer for incident neutron energies between threshold and 570 MeV. The proton-proton invariant mass distributions show a strong enhancement due to the pp(${}^1{S}_0$) final state interaction. A large anisotropy was found in the pion angular distributions in contrast to the reaction $pp\to pp{\pi }^0$. At small energies, a large forward/backward asymmetry has been observed. From the measured integrated cross section $\sigma (np\to \mathrm{p}p{\pi }^{-})$, the isoscalar cross section ${\sigma }_{01}$ has been extracted. Its energy dependence indicates that mainly partial waves with Sp final states contribute. Note: Due to a coding error, the differential cross sections $d\sigma /d{M}_{pp}$ as shown in Fig. 9 are too small by a factor of two, and inn Table 3 the differential cross sections $d\sigma /d{\Omega }_{\pi }^{\ast }$ are too large by a factor of $10/2\pi$. The integrated cross sections and all conclusions remain unchanged. A corresponding erratum has been submitted and accepted by European Physics Journal.

Comments: 18 pages, 16 figures