Screening effects in electron-positron pair production with capture in ultrarelativistic collisions

We study the influence of the shielding of the atomic nucleus by atomic ele ctrons on positron-electron pair production with capture in ultrarelativist ic nucleus-atom collisions. The importance of the shielding is shown to inc rease with the collision energy and with the atomic number of the target at om. We report calculations of cross sections for the pair production with c apture in collisions of 160 GeV/nucleon Pb82+ projectiles with different at omic targets ranging from Be to Au. Depending on the atomic number of the t arget the shielding is shown to reduce the cross sections by 2.5-14 percent at this collision energy. (C) 2000 Elsevier Science B.V. All rights reserv ed.