Peripheral pion production in projectile breakup reactions at 94 MeV/nucleon☆

Abstract Charged pion production has been observed in coincidence with the 4He projectile breakup channel in 16 O+ 27 Al reactions at 94 MeV/nucleon. Charged pions have been detected using a range telescope of plastic scintillators placed at 70°, 90° and 120° with respect to the beam direction. Helium nuclei have been detected using a multielement array of plastic scintillators covering the zenithal angular domain between 3° and 30° and the total azimuthal one. The velocity of the primary projectile-like nucleus (ν PLN ) has been reconstructed. The ν PLN distribution of coincidence events is shifted toward lower velocities with respect to that of inclusive events indicating a sharp coherent deceleration of the projectile when a pion is created. This could be an indication of collective mechanisms for pion production.