Elastic scattering loss of atoms from colliding Bose-Einstein condensate wavepackets

Bragg scattering can be used to create a daughter wavepacket with momentum k from a parent Bose-Einstein condensate, where k is very large compared to the momentum spread of the parent. Elastic collisions between atoms in the moving wavepacket and atoms in the parent results in formation of a shell of elastically scattered atoms with momentum k/2 that are lost from two original wavepackets. We apply a slowly-varying-envelope approximation to calculate the time-dependent dynamics of the two interacting wavepackets and account for the elastic scattering losses. A significant fraction of atoms can be lost this way from the parent and daughter wavepackets, especially if the motion is along the long axis of an asymmetric trap. We show that such elastic collisional losses lowers the output of four-wave mixing by around 20 percent for the experimental configuration in the NIST experimental demonstration of four-wave mixing of matter waves(Deng et al.), Nature 398, 218 (1999).