= Same-resonance entrance-channel cross-section ratio
{title2=$\sigma_a/\sigma_b=(g_a/g_b)(p_b^2/p_a^2)(\Gamma_a/\Gamma_b)$}
Compare two entrance channels feeding the same isolated resonance and the same selected exit channel, each at its own resonance <energy>. The exit <partial decay width> and the resonant denominator cancel. Different entrance momenta, <spin> weights and entrance widths remain. The formula assumes the same resonance, the stated unpolarized <spin> average and negligible nonresonant <interference>; a ratio at one shared laboratory <energy> would generally be different.
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