Contribution of the σ meson exchange to pionic double charge exchange reaction Xiao-fu Lü, B.S. Zou, Hui-ming Ding, Yu-xin Liu and En-guang Zhao Eur. Phys. J. A, 3 4 (1998) 377-380 Published online: 15 December 1998 DOI: 10.1007/s100500050192