OICC Press Journal of Theoretical and Applied Physics 2251-7235 11 4 2023 11 17 Two and three particles entanglement; helicity and spin with momentum 10.1007/s40094-017-0265-9 EN OICC Press Authors Various OICC Press Authors Journal Article 2023 11 17 AbstractConstruction of the reduced spin and helicity density matrix for systems of two and three particles are described by a wave packet with sharp and Gaussian momentum distribution. The entropy for the spin and helicity part of the systems is calculated from the viewpoint of moving observers.