Background subtraction methods for precision measurements of di-hadron and jet-hadron correlations in heavy ion collisions

摘要

Di-hadron correlations and jet-hadron correlations are frequently used tostudy interactions of the Quark Gluon Plasma with the hard partons that formjets. The existing background subtraction methods for these studies depend onseveral assumptions and independent measurements of the Fourier coefficients ofthe combinatorial background. In this paper, we present two backgroundsubtraction methods which use the observation that the near-side correlationsignal is negligible for large separations between the associated particle andthe trigger. The combinatorial background is fit in this background-dominatedregion. Including the reaction plane dependence of the raw correlation improvesthese results. To test the accuracy of these methods, a simple model is used tosimulate di-hadron and jet-hadron correlations with a combinatorial backgroundsimilar to that observed in the data. The true signal is compared to theextracted signal. The results are compared to results from two variants of theZero-Yield-At-Minimum (ZYAM) method. We test these methods for mid-peripheraland central collisions and for di-hadron and jet-hadron correlations. Thesemethods are more precise than the ZYAM method with fewer assumptions about theshape and level of the combinatorial background, even in central collisionswhere the experimental resolution on the measurement of the reaction planedependence is poor. These methods will allow more accurate studies ofmodifications of the away-side jet and will be particularly useful for studiesof jet-hadron correlations, where the combinatorial background is poorlyconstrained from previous studies.