Comparison of D --> K_s^0 pi and D --> K_L^0 pi Decay Rates

We present measurements of D -> K0_S pi and D -> K0_L pi branching fractions using 281 pb-1 of psi(3770) data at the CLEO-c experiment. We find that B(D0 -> K0_S pi0) is larger than B(D0 -> K0_L pi0), with an asymmetry of R(D0) = 0.108 ± 0.025 ± 0.024. For B(D+ -> K0_S pi+) and B(D+ -> K0_L pi+), we observe no measurable difference; the asymmetry is R(D+) = 0.022 ± 0.016 ± 0.018. The D0 asymmetry is consistent with the value based on the U-spin prediction A(D0 -> K0 pi0)/A(D0 -> K0bar pi0) = -tan^2(theta_C), where theta_C is the Cabibbo angle.