Hydrodynamic collectivity in proton–proton collisions at 13 TeV
Wenbin Zhao (Collaborative Innovation Center of Quantum Matter, Beijing, China, Department of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China); You Zhou (Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark); Hao-jie Xu (Department of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China, School of Science, Huzhou University, Huzhou, China); Weitian Deng (School of Physics, Huazhong University of Science and Technology, Wuhan, China); Huichao Song (Collaborative Innovation Center of Quantum Matter, Beijing, China, Center for High Energy Physics, Peking University, Beijing, China, Department of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China)
In this paper, we investigate the hydrodynamic collectivity in proton–proton (p–p) collisions at 13 TeV, using iEBE-VISHNU hybrid model with HIJING initial conditions. With properly tuned parameters, our model simulations can remarkably describe all the measured 2-particle correlations, including integrated and differential elliptic flow coefficients for all charged and identified hadrons (, Λ). However, our model calculations show positive 4-particle cumulant in high multiplicity pp collisions, and can not reproduce the negative measured in experiment. Further investigations on the HIJING initial conditions show that the fluctuations of the second order anisotropy coefficient increases with the increase of its mean value, which leads to a similar trend of the flow fluctuations. For a simultaneous description of the 2- and 4- particle cumulants within the hydrodynamic framework, it is required to have significant improvements on initial condition for pp collisions, which is still lacking of knowledge at the moment.
