  The properties of the entanglement entropy (EE) of two particle excited
states in a one-dimensional ring are studied. For a clean system we show
analytically that as long as the momenta of the two particles are not close,
the EE is twice the value of the EE of any single particle state. For almost
identical momenta the EE is lower than this value. The introduction of disorder
is numerically shown to lead to a decrease in the median EE of a two particle
excited state, while interactions (which have no effect for the clean case)
mitigate the decrease. For a ring which is of the same size as the localization
length, interaction increase the EE of a typical two particle excited state
above the clean system EE value.
