Effects of HBT correlations on flow measurements

Authors:
  • MDMai Dinh
    Mai Dinh
  • NBNicolas Borghini
    Nicolas Borghini
  • JOJean-Yves Ollitrault
    Jean-Yves Ollitrault
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Abstract
The methods currently used to measure collective flow in nucleus--nucleus collisions assume that the only azimuthal correlations between particles are those arising from their correlation with the reaction plane. However, quantum HBT correlations also produce short range azimuthal correlations between identical particles. This creates apparent azimuthal anisotropies of a few percent when pions are used to estimate the direction of the reaction plane. These should not be misinterpreted as originating from collective flow. In particular, we show that the peculiar behaviour of the directed and elliptic flow of pions observed by NA49 at low pT can be entirely understood in terms of HBT correlations. Such correlations also produce apparent higher harmonics of the azimuthal distribution, of the order of 1%, which should be looked for in the data.