2007/02/16 by M. J. Tannenbaum · 2 citations
Physics and Astronomy · #Distribution function #Feynman diagram #Fragmentation (computing) #Fragmentation function #Hadron #High-Energy Particle Collisions Research #Large Hadron Collider #Mathematical physics #Nuclear physics #Particle physics #Particle physics theoretical and experimental studies #Parton #Physics #Quantum Chromodynamics and Particle Interactions #Quantum mechanics #Scattering #nucl-ex
paper · pdf · doi:10.1142/s0218301307007386
published in International Journal of Modern Physics E 16(07n08), 2011-2017 (World Scientific) · 6 pages, 5 figures, Proceedings of Poster Session, 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006), November 14-20, 2006, Shanghai, P. R. China
arxiv created 2007/02/16 · openalex publication_date 2007/08/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Hard-scattering of point-like constituents (or partons) in p-p collisions was discovered at the CERN-ISR 1 in 1972 by measurements utilizing inclusive single or pairs of hadrons with large transverse momentum (p T ). Due to the steeply falling power-law p T spectrum of the hard-scattered partons, the inclusive single particle (e.g. π 0 ) p T t spectrum from parton fragmentation to a jet is dominated by trigger fragments with large z t ~ 0.7–0.8, where z t = p T t /p T jet is the fragmentation variable. It was generally assumed, following Feynman, Field and Fox, 2 as shown by data from the CERN-ISR experiments, that the p T a distribution of away side hadrons from a single particle trigger [with p T t ], corrected for z t , would be the same as that from a jet-trigger and follow the same fragmentation function as observed in e + e − or DIS. PHENIX 3 attempted to measure the fragmentation function from the away side x E ~ P T a /p T t distribution of charged particles triggered by a π 0 in p − p collisions at RHIC and showed by explicit calculation that the x E distribution is actually quite insensitive to the fragmentation function. Illustrations of the original arguments and ISR results will be presented. Then the lack of sensitivity to the fragmentation function will be explained, and an analytic formula for the x E distribution given, in terms of incomplete Gamma functions, for the case where the fragmentation function is exponential. The away-side distribution in this formulation has the nice property that it both exhibits x E scaling and is directly sensitive to the ratio of the away jet [Formula: see text] to that of the trigger jet, [Formula: see text], and thus can be used, for example, to measure the relative energy loss of the two jets from a hard-scattering which escape from the medium in A + A collisions. Comparisons of the analytical formula to RHIC measurements will be presented, including data from STAR 4,5 and PHENIX, 3,6 leading to some interesting conclusions.