Hypernuclear physics with pions

Abstract

We investigate the possibility of producing hypernuclei with energetic pion beams via the (..pi../sup +/, K/sup +/) reaction. Due to the high momentum transfer involved (qapprox. =300 MeV/c), even in the forward direction, the (..pi../sup +/, K/sup +/) reaction preferentially populates high-spin natural parity configurations obtained by coupling a ..lambda.. particle to a neutron hole. We present differential cross section calculations utilizing the plane-wave approximation (PWA), the distorted-wave impulse approximation (DWIA) using fully distorted-waves, and the eikonal approximation (EIK) to approximate distortion effects. The DWIA and EIK results are in agreement, and lead to cross sections typically a factor of 5 --10 lower than the PWA results, due to absorptive effects. Cross sections of 5 --20 ..mu..b/sr at 0/sup 0/ are obtained in the DWIA for high-spin natural-parity ''stretched configurations,'' for example (/sub ..lambda../d/sub 3/2,5/2/x/sub n/ f/sub 7/2//sup -1/)/sub 5/- or (/sub ..lambda../f/sub 5/2,7/2/x /sub n/ f/sub 7/2//sup -1/)/sub 6/+ in /sub ..lambda..//sup 48//Ca, for pion lab momentum p/sub ..pi../ in the range 1.02--1.1 GeV/c, where the elementary cross section for K/sup +/n..--> pi../sup +/..lambda.. has its peak values. The cross sections for the population of the natural-parity ground-state levels (/sub ..lambda../S/sub 1/2/x/sub n/l/sub l/+1/2 /sup -1/)/sub J/=l with closed-shellmore » targets remain above 2 ..mu..b/sr at 0/sup 0/ for systems lighter than Aapprox. =50. The cross sections drop rapidly below p/sub ..pi../=1.02 GeV/c, due to threshold effects. Results are presented for the calculated quasielastic (quasifree) continuum background for the (..pi../sup +/, K/sup +/) reaction as a function of theta/sub 1ab/ and hypernuclear excitation energy. Because of the higher momentum transfer the quasielastic background is broader and significantly less in magnitude than that obtained in the (K/sup -/,..pi../sup -/) reaction at 0/sup 0/.« less