Estimating relative luminosity for RHIC spin physics

Relative luminosities for different beam spin states must be determined to better than 10−4–10−3 in order to measure spin asymmetries to the desired accuracy at RHIC. It is demonstrated that biases due to high rates in luminosity monitors can be kept acceptably small for anticipated RHIC operating conditions. Additionally, the distribution of the estimates is shown to be approximately Gaussian (normal) with known mean and standard error, permitting the construction of confidence intervals for the true spin asymmetry.