According to the unfolding study at 7.7 GeV 0-5% (here), two-component structure predicted by Phys.Rev,C 98.054901(2018) is likely there. In order to investigate the origin of the second component at smaller part of the net-proton distribution, events having protons less than 10 at 0-5% centrality are shown as a function of run index. It is found that those events with extremely small number of protons are mainly coming from specific run durations.




Within runs #11125089-#11126067, we picked up 15 events having protons less than 10, and plotted various track-wise quantities for each event, see here. It was found in those strange events DCA distribution looks strange, which has mean value ~1.0. Since in higher-moment analysis DCA cut < 1.0cm is applied, number of protons become extremely small for those events. In addition, the strange DCA distribution is found to be caused by the shift of signed DCA_xy distribution (normally around zero).


<DCA_xy> as a function of event ID for each run has been checked at 7.7GeV 0-5% centrality, which is summarized here. Below is an example for strange events having drop of <DCA_xy> at the beginning of the run. Green and blue solid lines are mean and +/- 7sigma determined for whole data sets (note that in some other energies mean and sigma are determined for each run, since those are unstable). The last event ID which daviates from mean +/- 7sigma, plus 20k (for safety) is defined as a "event boundary". For 7.7 GeV, all events before the event boundary are removed from the cumulant calculations.

- The same checks have been done in 11.5, 14.5, 19.6, 27, 54.4 and 62.4 GeV as well. See the attached PDF files "DCAXY_*GeV.pdf" (large file is splitted into several).
- Similar drop of <DCA_xy> at the beginning of the run is also observed in 11.5 GeV.
- The drop of <DCA_xy> at the end of some runs is observed in 14.5, 19.6, 27 and 62.4 GeV. All events above the event boundary are removed from the cumulant calculations. Below is one example for 62.4 GeV 0-5% centrality.

- The drop of <DCA_xy> at the middle of some runs is observed in 19.6, 27 and 62.4 GeV. All events between two event boundaries are removed from the cumulant calculations. Below is one example for 62.4 GeV 0-5% centrality.



- For 19.6 and 62.4 GeV, some shift of <DCA_xy> is observed (the plots below are for 19.6 GeV ). Those runs are removed from the analysis.