  The emergent integrability in a many-body localized (MBL) system can be well
characterized by the existence of the complete set of local integrals of motion
(LIOMs). Such exactly conserved and exponentially localized operators are often
understood as quasiparticle operators which can be expanded in terms of
single-particle operators dressed with different numbers of particle-hole
pairs. Here, we consider a one-dimensional XXZ spin-$\frac12$ Heisenberg chain
in the presence of a random field and try to quantify the corrections needed to
be considered in the picture of quasiparticles associated with LIOMs due to the
presence of particle-hole excitations. To this end, we explicitly present the
multibody expansion of LIOM creation operators of the system in the MBL regime.
We analytically obtain the coefficients of this expansion and discuss the
effect of higher-order corrections associated with different numbers of
particle-hole excitations. Our analysis shows that depending on the
localization length of the system, there exist a regime in which the
contributions that come from higher-order terms can break down the effective
one-particle description of the LIOMs and such quasiparticles become
essentially many-body-like.
