A particlo of enorgy \( E \) is scattored off a ono-dimonsional potontiall \( \lambda \delta(x) \), whore \( \lambda \) is a real positive constant, with a transmission ampitude \( z_{1} \). In a different experiment, the same particlo is scattored off anothor one-dimensional potontial \( -\lambda \delta(x) \), with a transmission amplitudo \( L_{\text {}} \). In the limil \( E \rightarrow 0 \), the phase difference botwoen \( t_{+} \)and \( t_{-} \)is
1. \( \pi / 2 \)
2. \( \pi \)
3. 0
4. \( 3 \pi / 2 \)