Control-region transfer factor ($b_{\mathrm{SR}}=T{b}_{\mathrm{CR}}$)

A ratio translating a background yield in a particle-physics control region into its yield in a signal region. It may be estimated with simulation and calibration measurements. Its uncertainty must include acceptance, response and physics differences between the regions; contaminating backgrounds are subtracted or fitted jointly. A profile likelihood can constrain the control and signal counts together rather than treating the transferred estimate as exact.