Normalized multi-pion Hanbury–Brown–Twiss correlation functions of pion-emitting sources with Bose–Einstein condensation

Abstract

Recently, the ALICE collaboration analyzed the three- and four-pion Hanbury\nBrown-Twiss (HBT) correlations in Pb-Pb collisions at the Large Hadron Collider\n(LHC). The measured suppressions of three- and four-pion correlations may\noriginate from a substantial coherence of the particle-emitting sources. In\nthis work we investigate the normalized three- and four-pion HBT correlation\nfunctions for evolving pion gas (EPG) sources with Bose-Einstein condensation.\nWe find that the intercepts of the normalized correlation functions at zero\nrelative momentum are sensitive to source condensation and particle momentum.\nThe normalized correlation functions in low average-momentum regions of three\nand four pions decrease with decreasing temperature and increasing particle\nnumber of the source, indicating a dependence of the normalized correlation\nfunctions on source condensation. However, this dependence becomes weak in an\nintermediate average-momentum region because particles with high momenta are\nlikely emitted from excited states incoherently in the EPG model, even if the\nsource has a considerable condensation fraction. For a wide momentum range, the\nnormalized correlation functions for low source temperatures are enhanced at\nlarger relative momenta because of a rapid increase of two-pion chaoticity\nparameter with increasing particle momentum. We hope the significant\nenhancement of the normalized four-pion correlation function at high relative\nmomentum will be identified through future analyses of experimental data.\n