“…To understand these observables in experiments and QGP phase transition, there are also some open questions for small collision systems (such as C + C or O + O collisions) as well as large collision systems (such as Au + Au or Pb + Pb collisions), (1) how to understand transformation coefficient from initial geometry distribution or fluctuation to momentum distribution at final stage in hydrodynamical mechanism [20,[28][29][30]; (2) how to understand similar phenomena for some observables for small systems with high multiplicity and large systems [9,10,[31][32][33][34][35][36][37]; (3) does the matter created in different size of system undergo the similar dy-namical process and have similar viscosity [38,39]?, and the last two questions are closely related. Recently the small system experiments were proposed for RHIC-STAR [40] and LHC-ALICE [41] to study the initial geometry distribution and fluctuations effects on momentum distribution at final stage.…”