Ionization Energy Loss of Relativistic Electrons in Thin Silicon Detectors

We have measured the ionization loss of electrons with Lorentz factors γ=2.91 and 1.6×10⁴<~γ<~10⁵ passing through a (100.71 ±{} 0.15)-{μ}m silicon detector. Our results are in agreement with accepted theory for γ=2.91 and γ=1.6×10⁴; however, for γ>~3×10⁴ our results are systematically (7 ±{} 2)% below the theoretical value. We suggest an explanation in terms of the finite detector thickness and a relativistic effect.