Probing medium-induced energy loss with direct jet reconstruction in p+p and Cu+Cu collisions at PHENIX

Abstract

We present the application of a new jet reconstruction algorithm that uses a Gaussian filter to locate and reconstruct the jet energy to p + p and heavy ion data from the PHENIX detector. This algorithm is combined with a fake jet rejection scheme that provides efficient jet reconstruction with an acceptable fake rate. We show our first results on the measured jet spectra, and on jet-jet angular correlation in p+p and Cu+Cu collisions.The study of jet physics at RHIC plays an important role in understanding the parton-medium interaction, in-medium fragmentation properties, and applied to the RHIC spin program, also the study of the proton structure. We therefore set out to systematically investigate the feasibility of, and the appropriate approach of performing jet reconstruction using a limited aperture detector like the PHENIX central arms [1] and including heavy ion collision systems. Neither is a wellstudied aspect of jet reconstruction, and both have been considered as challenging [2].We observed that the flat weighting in traditional jet reconstruction algorithms is particularly prone to fluctuations at large angle. A similiar effect also exists at the PHENIX central arm edges, here due to the lack of balancing fragments. Both issues can be effectively addressed by a nonflat weighting that smoothly dampens large angle fragments. Furthermore, the energy flow variable as proposed by Sterman et al. [3] suggests that angular convolution of the event p T

The radiation pattern of a QCD antenna in a dense medium

“…To reduce the complexity of the calculation and since the dominating scale in this regime is r −1 ⊥ Q s we neglect for the time being the effect of broadening. 9 In this regime we expand the decoherence parameter, obtaining…”

“…These observations established the phenomenon known as 'jet quenching,' namely the interaction of a hard parton with the dense medium created in the aftermath of the collision, as one of the key discoveries of the high-energy heavy-ion program [3][4][5][6]. Complementary, more differential observables such as multi-particle correlations and full jet reconstruction in heavy-ion events probe the structure of the energy and particle distributions of jets traversing the quark-gluon plasma [7][8][9][10][11][12][13] and provide strong constraints on the theoretical modeling of multi-gluon emissions in the medium.…”

Jet coherence in QCD media: the antenna radiation spectrum

“…With the gauge choice above only the transverse component of the gauge field is dynamical. Its linear response to the medium interaction reads [24] A 8) where the medium field A µ med only has a negative light-cone component which, in the limit considered above, is related to the medium color source density through the Poisson equation…”

“…Indeed, strong medium effects are observed in heavy-ion collisions for both single-inclusive leading particle spectra [1][2][3] and two-particle correlations [4,5]. While such measurements have reached a high level of sophistication, shedding light on qualitative aspects of the quark-gluon plasma, studies of intrajet distributions in heavy ion collisions have recently been initiated both at RHIC [6][7][8] and LHC [9][10][11] with many promising results and prospects for the future.…”

A local Monte Carlo framework for coherent QCD parton energy loss

“…In this context, we mention that first preliminary results on reconstructed jet measurements have become available at RHIC [5][6][7] within the last two years. With the much wider kinematic reach accessible at the LHC, numerous novel opportunities for studying jet quenching emerge now.…”