Extraction of the spectral functions of the virtual decays alpha --> tp and alpha --> tau n from data on the reactions alpha p --> tpp and alpha p --> tau pn for incident alpha-particle momentum 2.7 GeV/c

A 2-m liquid-hydrogen bubble chamber was exposed to a separated beam of alpha particles from the ITEP synchrotron. The momentum of the incident He-4 nuclei, averaged over the fiducial volume of the chamber, was 2.7 GeV/c (the kinetic energy of the incident protons in the rest frame of the nucleus was T(p) = 220 MeV). The spectral functions for the decays alpha --> tp and alpha --> taun, extracted from the exclusive reactions alphap --> tpp and alphap --> taupn, are identical within the experimental errors. By extrapolating the nuclear vertex function to the pole a lower bound is obtained for the corresponding vertex constant. The experimental data are compared with the results of other studies and with theoretical calculations.