Time-reversal invariance for strong interactions, in particular for that part of the force which flips the spin of the proton, has been tested by comparing the polarization and asymmetry in the elastic scattering of 32.9-MeV protons from ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ at 60°. By making the measurements for ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ relative to ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, where spin flip is forbidden except in case of parity nonconservation, we avoid the need to measure either an absolute beam polarization or absolute analyzing power. Our first result is that the polarization and asymmetry are equal to ±2.5%; consequently, we observe no violation of time-reversal invariance.

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