Subthreshold K+ production in deuteron and alpha induced nuclear reactions

Abstract Double differential cross sections d 2 σ/dpdΩ have been measured for π + and K + emitted around midrapidity in d + A and α + A collisions at a beam kinetic energy of 1.15 GeV/nucleon. The total π + yield increases by a factor of about 2 when using an alpha projectile instead of a deuteron whereas the K + yield increases by a factor of about 4. According to transport calculations, the K + enhancement depends both on the number of hadron-hadron collisions and on the energy available in those collisions: their center-of-mass energy increases with increasing number of projectile nucleons.