Velocity-dependent transverse momentum distribution of fragments produced fromAr40+Be9at 95 MeV/nucleon

Abstract

Transverse momentum $({P}_{\mathrm{T}})$ distributions of projectilelike fragments produced at intermediate energy are investigated. ${P}_{\mathrm{T}}$ distributions of fragments with mass ${A}_{\mathrm{F}}\phantom{\rule{4pt}{0ex}}=10--37$, produced from an $^{40}\mathrm{Ar}$ beam with $E=95\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}/\mathrm{nucleon}$ and a Be target, are observed as a function of fragment velocity by using the Rikagaku Kenkyusho (RIKEN) Projectile Fragment Separator at RIKEN. The width of ${P}_{\mathrm{T}}$ distribution $({\ensuremath{\sigma}}_{\mathrm{T}})$ decreases monotonically with longitudinal momentum $({P}_{\mathrm{L}})$. The decreasing trend shows a clear dependence on fragment mass. The observed ${\ensuremath{\sigma}}_{\mathrm{T}}$ is analyzed with a linear function and successfully reproduced by a parameter to characterize the decreasing trend. ${\ensuremath{\sigma}}_{\mathrm{T}}$ at the primary beam velocity shows good agreement with the Goldhaber formula, which is obtained on the basis of the contribution of the Fermi momentum. In contrast, the ${\ensuremath{\sigma}}_{\mathrm{T}}$ at the center of the ${P}_{\mathrm{L}}$ distribution as determined by using the fits and parametrized energy loss in the fragmentation process is consistent with the width, which includes an additional contribution from the orbital deflection of the projectile. The antisymmetrized molecular-dynamics calculation indicates that the contribution of impact parameters is an important factor in understanding the behavior of the ${P}_{\mathrm{T}}$ distribution. In addition, the practical formulation for ${\ensuremath{\sigma}}_{\mathrm{T}}$ obtained in the present study enables a reliable characterization of the fragments, which would be applicable to various research fields involving, for example, radioactive nuclear beams.