Identity method reexamined

This paper discusses the impact of finite particle losses associated with instrumental effects in measurements of moments of produced multiplicities with the identity method towards the evaluation of fluctuation measures such as ${\nu }_{\mathrm{dyn}}$. One finds that the identity method remains applicable provided it is modified to determine factorial moments $\langle N(N-1)\rangle$, rather than moments $\langle N^2\rangle$. It is further demonstrated that ${\nu }_{\mathrm{dyn}}$ remains robust if detection efficiencies are uniform across the measurement's acceptance. The robustness is lost, however, if detection efficiencies are momentum dependent, although the identity method remains applicable provided detection efficiencies can be determined with sufficient accuracy.