Search for 4n IN π− double charge exchange reactions with heavy nuclei

A search for the existence of the tetraneutron has been made using the double charge exchange reaction π − + 208 Pb → 4 n + π + + residuals for 4n production and the capture process in the same target, 208 Pb + 4 n → 212 Pb + γ , for the 4n detection. No event has been found, giving an upper limit for the product of the production cross section σp, the detection cross section σd and the 4n lifetime τ. Assuming 10−18 ≦ τ ≦ 10−9 sec it follows that σpσdτ ≦ 2.5 × 10−65cm4 sec with 90 % confidence, and for τ ≧ 10 −9 sec , σ p σ d ≦ 2.5 × 10 −56 cm 4 with 90 % confidence. The magnitude of this value is comparable to the experimental limit of the 4He(π−, π+)4n cross section.