  Signatures of the dissipation region of collisionless magnetic reconnection
are investigated by the Geotail spacecraft for the 15 May 2003 event. The
energy dissipation in the rest frame of the electron's bulk flow is considered
in an approximate form D*_e, which is validated by a particle-in-cell
simulation. The dissipation measure is directly evaluated from the {plasma
moments}, the electric field, and the magnetic field. Using D*_e, a compact
dissipation region is successfully detected in the vicinity of the possible
X-point in Geotail data. The dissipation rate is 45 pWm**{-3}. The length of
the dissipation region is estimated to 1--2 local ion inertial length. The
Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced.
It is positive over the reconnection region and it has a peak around the pileup
region away from the X-point. These new measures D*_e and W provide useful
information to understand the reconnection structure.
