We performed systematic studies on the effects of event-by-event efficiency fluctuations on efficiency correction for cumulant analysis in relativistic heavy-ion collision experiments. Experimentally, particle eficien...We performed systematic studies on the effects of event-by-event efficiency fluctuations on efficiency correction for cumulant analysis in relativistic heavy-ion collision experiments. Experimentally, particle eficiencies of events measured under different experimental conditions should be different. For fluctuation measurements, the final event-by-event multiplicity distributions should be the superposed distributions of various type of events measured under different conditions. We demonstrate efficiency fluctuation effects using numerical simulation, in which we construct an event ensemble consisting of events with two different efficiencies. By using the mean particle efficiencies, we find that the efficiency corrected cumulants show large deviations from the original inputs when the discrepancy between the two efficiencies is large. We further studied the effects of efficiency fluctuations for the cumulants of net-proton distributions by implementing the UrQMD events of Au＋Au collisions at √SNN=7.7 GeV in a realistic STAR detector acceptance. We consider the unequal efficiency in two sides of the Time Projection Chamber （TPC）, multiplicity dependent efficiency, and the event-by-event variations of the collision vertex position along the longitudinal direction （Vz）. When the efficiencies fluctuate dramatically within the studied event sample, the effects of efficiency fluctuations have significant impacts on the efficiency corrections of cumulants with the mean efficiencies. We find that this effect can be effectively suppressed by binning the entire event ensemble into various sub-event samples, in which the efficiency variations are relatively small. The final efficiency corrected cumulants can be calculated from the weighted average of the corrected factorial moments of the sub-event samples with the mean efficiencies.展开更多
We studied the effects of centrality fluctuation and deuteron formation on the cumulant(C_(n))and correlation functions(K_(n))of protons up to the sixth order in the most central(b<3 fm)Au+Au collisions at√SNN=3 G...We studied the effects of centrality fluctuation and deuteron formation on the cumulant(C_(n))and correlation functions(K_(n))of protons up to the sixth order in the most central(b<3 fm)Au+Au collisions at√SNN=3 GeV in a microscopic transport model(JAM).The results are presented as a function of rapidity acceptance within the transverse momentum 0.4<p T<2 GeV/c.We compared the results obtained by the centrality bin width correction(CBWC)using charged reference particle multiplicities with the CBWC using impact parameter bins.It was found that,at low energies,the centrality resolution for determining the collision centrality using charged particle multiplicities is not sufficient to reduce the initial volume fluctuation effect for higher-order cumulant analysis.New methods need to be developed to classify events with high centrality resolution for heavy-ion collisions at low energies.Finally,we observed that the formation of deuterons suppresses the higher-order cumulants and correlation functions of protons and found it to be similar to the efficiency effect.This work can serve as a noncritical baseline for the QCD critical point search in the high baryon density region.展开更多
基金Supported by the MoST of China 973-Project No.2015CB856901NSFC(11575069)
文摘We performed systematic studies on the effects of event-by-event efficiency fluctuations on efficiency correction for cumulant analysis in relativistic heavy-ion collision experiments. Experimentally, particle eficiencies of events measured under different experimental conditions should be different. For fluctuation measurements, the final event-by-event multiplicity distributions should be the superposed distributions of various type of events measured under different conditions. We demonstrate efficiency fluctuation effects using numerical simulation, in which we construct an event ensemble consisting of events with two different efficiencies. By using the mean particle efficiencies, we find that the efficiency corrected cumulants show large deviations from the original inputs when the discrepancy between the two efficiencies is large. We further studied the effects of efficiency fluctuations for the cumulants of net-proton distributions by implementing the UrQMD events of Au＋Au collisions at √SNN=7.7 GeV in a realistic STAR detector acceptance. We consider the unequal efficiency in two sides of the Time Projection Chamber （TPC）, multiplicity dependent efficiency, and the event-by-event variations of the collision vertex position along the longitudinal direction （Vz）. When the efficiencies fluctuate dramatically within the studied event sample, the effects of efficiency fluctuations have significant impacts on the efficiency corrections of cumulants with the mean efficiencies. We find that this effect can be effectively suppressed by binning the entire event ensemble into various sub-event samples, in which the efficiency variations are relatively small. The final efficiency corrected cumulants can be calculated from the weighted average of the corrected factorial moments of the sub-event samples with the mean efficiencies.
基金Supported by the National Key Research and Development Program of China(2020YFE0202002,2018YFE0205201)the National Natural Science Foundation of China(11828500,11828501,11575069,11890711,11861131009)。
文摘We studied the effects of centrality fluctuation and deuteron formation on the cumulant(C_(n))and correlation functions(K_(n))of protons up to the sixth order in the most central(b<3 fm)Au+Au collisions at√SNN=3 GeV in a microscopic transport model(JAM).The results are presented as a function of rapidity acceptance within the transverse momentum 0.4<p T<2 GeV/c.We compared the results obtained by the centrality bin width correction(CBWC)using charged reference particle multiplicities with the CBWC using impact parameter bins.It was found that,at low energies,the centrality resolution for determining the collision centrality using charged particle multiplicities is not sufficient to reduce the initial volume fluctuation effect for higher-order cumulant analysis.New methods need to be developed to classify events with high centrality resolution for heavy-ion collisions at low energies.Finally,we observed that the formation of deuterons suppresses the higher-order cumulants and correlation functions of protons and found it to be similar to the efficiency effect.This work can serve as a noncritical baseline for the QCD critical point search in the high baryon density region.
