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

Abstract 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 4 n production and the capture process in the same target, 208 Pb + 4 n → 212 Pb + γ , for the 4 n detection. No event has been found, giving an upper limit for the product of the production cross section σ p , the detection cross section σ d and the 4 n lifetime τ. Assuming 10 −18 ≦ τ ≦ 10 −9 sec it follows that σ p σ d τ ≦ 2.5 × 10 −65 cm 4 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 4 He( π − , π + ) 4 n cross section.