The concept of missing energy is commonly applied in hadron colliders. The initial momentum of the colliding partons along the beam axis is not known — the energy of each hadron is split, and constantly exchanged, between its constituents — so the amount of total missing energy cannot be determined. However, the initial energy in particles traveling transverse to the beam axis is zero, so any net momentum in the transverse direction indicates missing transverse energy, also called missing E T or MET.