sPHENIX is a new experiment under construction for the Relativistic Heavy Ion
Collider at Brookhaven National Laboratory which will study the quark-gluon
plasma to further the understanding of QCD matter and interactions. A prototype
of the sPHENIX electromagnetic calorimeter (EMCal) was tested at the Fermilab
Test Beam Facility in Spring 2018 as experiment T-1044. The EMCal prototype
corresponds to a solid angle of $ \Delta \eta \times \Delta \phi = 0.2 \times
0.2$ centered at pseudo-rapidity $\eta = 1$. The prototype consists of
scintillating fibers embedded in a mix of tungsten powder and epoxy. The fibers
project back approximately to the center of the sPHENIX detector, giving 2D
projectivity. The energy response of the EMCal prototype was studied as a
function of position and input energy. The energy resolution of the EMCal
prototype was obtained after applying a position dependent energy correction
and a beam profile correction. Two separate position dependent corrections were
considered. The EMCal energy resolution was found to be $\sigma(E)/\langle
E\rangle = 3.5(0.1) \oplus 13.3(0.2)/\sqrt{E}$ based on the hodoscope position
dependent correction, and $\sigma(E)/\langle E\rangle = 3.0(0.1) \oplus
15.4(0.3)/\sqrt{E}$ based on the cluster position dependent correction. These
energy resolution results meet the requirements of the sPHENIX physics program.
