NN(${}^1{S}_0$) pairs in ${}^3$He and in p${}^3$He backward elastic scattering

Abstract

It is shown that the shoulder observed in the cross section of $p^{3}He$ backward elastic scattering at proton beam energies of 0.4 -- 0.7 GeV can be explained by the mechanism of virtual $\pi$-meson production with a dominant contribution from the subprocesses $p{d}^{\ast }{\to }^3$He${\pi }^0$ and $p(pp){\to }^3$He${\pi }^{+}$, where $d^{\ast }$ denotes the singlet deuteron and the $pp$ pair is in the ${}^1{S}_0$ state. At high energies, 1-3 GeV, the mechanism of $np$-pair transfer dominates and probes high-momentum $NN{(}^1{S}_0$) correlations in ${}^3$He.

3 pages, Latex, 1 postscript figure. Contribution to the 17th International IUPAP Conference on Few-body Problems in Physics, June 5-10, 2003 Durham, North Carolina, USA. Uses espcrc1.sty