Direct jet reconstruction in image and Cu + Cu collisions at PHENIX

Direct jet reconstruction in heavy ion collisions is an important probe for the in-medium parton energy loss and jet–medium interactions and reconstructed jets provide additional constraints to characterize the underlying mechanisms. However, traditional jet reconstruction algorithms operating in the large soft background at RHIC produce fake jets well above the intrinsic production rate of high-image hard scattering, thus impeding the detection of the low cross section jet signal at RHIC energies. We developed a jet reconstruction algorithm that locates and reconstructs the jet energy using a Gaussian filter. This algorithm is combined with a fake jet rejection scheme that provides efficient jet reconstruction with acceptable fake rate in a background environment up to the central Au + Au collision at image. We present results of its application in image and Cu + Cu collisions using data from the PHENIX detector, including jet spectrum up to 60 GeV/c, nuclear modification factor, and fragmentation function.