## Dividing by mixed-events for acceptance correction is wrong    [PDF]

Lingshan Xu, Chin-Hao Chen, Fuqiang Wang
We point out that the mixed-event method for two-particle acceptance correction, widely used in particle correlation measurements at RHIC and LHC, is wrong. The correct acceptance should be the convoluted distribution from two single-particle efficiency X acceptance distributions. The error of the mixed-event method, which guarantees a uniform \Delta\eta\ two-particle combinatorial density, is however small in correlation analyses where the two particles are integrated over an extended \eta\ range. With one particle fixed in \eta\ and the right acceptance correction, the background-subtracted correlated pair density may reveal a \Delta\eta\ dependence. This has important physics implication, and may provide crucial information to disentangle physics mechanisms for the recently observed long-range ridge correlation in asymmetric p+Pb collisions at the LHC.
View original: http://arxiv.org/abs/1304.8120