Acceptance corrections to net baryon and net charge cumulants

Abstract

We show that the effect of finite acceptance drastically influences the net-baryon and net-charge cumulants, which are believed to be sensitive probes of the QCD phase diagram. We derive general formulas that relate the true cumulants ${K}_{n}$ which reflect the full dynamics of the system with the actually measured cumulants ${c}_{n}$ for a given acceptance, modeled by a binomial probability parameter $p$. We find that this relation involves additional moments which cannot be expressed by cumulants and should be measured in order to extract any potential information about the QCD critical point. We demonstrate that for a wide range of the true cumulant ratios ${K}_{n}/{K}_{m}$ the measured ratios ${c}_{n}/{c}_{m}$ quickly converge if $p<1/2$, which makes the interpretation of the data very challenging, especially in case of the net-proton cumulants. Our study further suggests that the measurement of net-charge cumulants may be more advantageous for the investigation of the QCD phase diagram.