Influence of preferential emission of pions on pion interferometry

In this paper, the influence of the preferential emission of pions on the analyzed results from two-pion interferometry was studied. In relativistic mass-asymmetric nucleus-nucleus collisions, the azimuthal distribution of pions is anisotropic because of the shadowing effect of the heavy target spectators, consequently, correlation independent of Bose-Einstein statistics is observed among the pions. Then the spatial parameter of the source extracted from pion interferometry is less than the true value due to this correlation. This influence can be corrected by rotating the events so that their estimated reaction planes are parallel to each other before constructing the background. For collisions of 1.8A GeV Ar+Pb at the Bevalac streamer chamber, the previous result for the spatial parameter from two-pion interferometry is R=5.53±0.38 fm. After correction, the result for the spatial parameter is R=5.87±0.45 fm.