  Magnetic reconnection plays an important role in the release of magnetic
energy and consequent energization of particles in collisionless plasmas.
Energy transfer in collisionless magnetic reconnection is inherently a two-step
process: reversible, collisionless energization of particles by the electric
field, followed by collisional thermalization of that energy, leading to
irreversible plasma heating. Gyrokinetic numerical simulations are used to
explore the first step of electron energization, and we generate the first
examples of field-particle correlation (FPC) signatures of electron
energization in 2D strong-guide-field collisionless magnetic reconnection. We
determine these velocity space signatures at the x-point and in the exhaust,
the regions of the reconnection geometry in which the electron energization
primarily occurs. Modeling of these velocity-space signatures shows that, in
the strong-guide-field limit, the energization of electrons occurs through bulk
acceleration of the out-of-plane electron flow by parallel electric field that
drives the reconnection, a non-resonant mechanism of energization. We explore
the variation of these velocity-space signatures over the plasma beta range
$0.01 \le \beta_i \le 1$. Our analysis goes beyond the fluid picture of the
plasma dynamics and exploits the kinetic features of electron energization in
the exhaust region to propose a single-point diagnostic which can potentially
identify a reconnection exhaust region using spacecraft observations.
