No abstract

Several authors have proposed the existence of new particles and n -n resonances. 1 " 5 Along these lines we are studying the reactions p + d-+\ p + d-~ < He 3 + 77° He 3 + a; 0 He 3^-^4 "^^1" He 3 + 7r°+7r°

The MuCap experiment at the Paul Scherrer Institute has measured the rate ΛS of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1 %. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. ΛS is determined from the difference between the µ − disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 × 10 10 µ − decays, from which we extract the capture rate Λ S = (714.9 ± 5.4stat ± 5.1syst) s −1 and derive the proton's pseudoscalar coupling g P (q 2 0 = −0.88 m 2 µ ) = 8.06 ± 0.55.