  An original entity is defined to study quantum beams of conserved particles.
The beam is described as a Stationary Incoherent Superposition of Wave packets
(SISOW). Mean values are time-independent confirming that the SISOW describes a
stationary flux of particles. The SISOW is a general entity that contains the
Hamiltonian eigenstates as a particular limit. The decomposition of the SISOW
into wave packets provides intrinsic dynamic information which is not
accessible from Hamiltonian eigenstates. The SISOW provides and adequate
framework to study mesoscopic systems
