Analyses of multi-pion Bose-Einstein correlations for the granular sources with coherent pion-emission droplets

ALICE Collaboration measured the three- and four-pion Bose-Einstein correlations (BECs) in Pb-Pb collisions at the Large Hadron Collider (LHC). It is speculated that the significant suppressions of multi-pion BECs are due to a considerable degree of coherent pion emission in the collisions. To explain the observed suppressions, we study the multi-pion BEC functions in a granular source model with coherent pion-emission droplets. We find that the intercepts of multi-pion correlation functions at the relative momenta near zero are sensitive to the droplet number in the granular source. They decrease with decreasing droplet number. The model results of three- and four-pion correlation functions are in basic agreement with the experimental data in central Pb-Pb collisions at the LHC. The normalized four-pion correlation function is sensitive to the momentum dependence of emission coherence. Its rise in moderate relative-momentum region is a signal that high-momentum pions are more possibly emitted chaotically compared to low-momentum pions which may condense in the ground state due to identical boson condensation.