Transverse momentum correlations between particle-particle pairs as a probe of effective emitter mass: ⁴⁰Ar+^natAg (E/A=7, 17, 27, and 34 MeV)

Average transverse momenta have been carefully measured for α-particle pairs at laboratory angles of 21°, 31°, 47°, and 67°. They exhibit small but distinct shifts for different relative azimuthal angles Δcphi. Detection on the same side of the beam (Δcphi≊24°) yields a smaller average tranverse momentum or energy than on the opposite side (Δcphi≊168°). For α-α pairs detected at ≊67° to the beam these small shifts are analyzed with a recoil model to extract the average emitter mass for the first α particle from the coincident pairs. The results are A=130±10 to 115±10 for reactions of ^107,109Ag with ⁴⁰Ar for 7A and 34A MeV, respectively. The particle pairs emitted at 21° are produced from more complex source mixtures. There is evidence from p-Li and α-Li pairs that Li fragments are emitted after protons or α particles in ≊1/2 of the events. The overall pattern is consistent with incomplete fusion leading to the formation of a hot, essentially thermalized composite nucleus and its associated statistical decay.