Effects of Spontaneous Detector Decorrelation on Measurements of High-Order Cumulants in the Search for the QCD Critical Point*

Fluctuations of conserved charges in heavy-ion collisions are expected to be sensitive to a critical point in the phase diagram of QCD matter. These fluctuations can be quantified by measuring various orders of cumulants, C_n, of the distributions of baryon number, charge, strangeness, and p_T. The collision-energy dependence of net-proton C₄/C₂ from STAR's measurements in Beam Energy Scan I hinted at a possible non-monotonic deviaton from the non-critical baseline from √s_NN = 7.7 GeV to 19.6 GeV. We present a discussion of the difficulties with using multiple detectors in measurements of high-order cumulants. The effect of the correlation between particle identification detectors and multiplicity detectors will be explored. We will demonstrate using UrQMD simulations and a toy model of a detector how a false signal can be caused by rare events, and how to fix this. Implications for STAR's Beam Energy Scan II and Fixed-Target Program measurements will be discussed.