A study of the dynamical-fluctuation property inside jets in e+e? collisions

Gang CHEN
2003 Science in China Series G  
A study of the dynamical-fluctuation property of 2-jet events is carried out. It is found that the dynamical fluctuations of the hadronic system inside 2-jet events change with the variation of the cut parameter y cut . There is a transition point, where the dynamical fluctuations in these systems are circular in the transverse plane; and are elliptical in the longitudinal-transverse planes. It is shown that this transition point corresponds to the scale of visible jets. Meanwhile, the
more » ... while, the dynamical fluctuation properties inside a single-jet in 2-jet and 3-jet events are compared. The dynamical fluctuations inside quark-and gluon-jets are found to be qualitatively different. A scale for the "visible gluon jet" production is thus obtained. As is well known, the matter system with quark and gluon as the basic elements has been established. However, these basic elements of matter, unlike the atoms and nuclei, are unable to be observed directly by experiments. According to the theory of strong interactionüquantum chromodynamics (QCD), the strong interaction has the special property of both asymptotic freedom and colour confinement. The quarks and gluons, produced in whichever process and at whatever time, will fragment into final-state hadrons before being observed experimentally. In any process, even though the energy scale Q 2 is large enough for perturbative QCD (pQCD) to be applicable, there must be a non-perturbative hadronization phase before the final state particles can be observed. Therefore, the transition or interplay between hard and soft processes is a very important problem. In high energy experiments, the produced partons are usually moving with high momentum. Their fragmentation results in groups of hadrons, forming a circular cone, called jet. The detection of jets is the most direct method for the experimental observation of partons. Historically, the discovery in 1975 [1] of a two-jet structure in e + e − annihilation at c.m. energies higher than 6 GeV has been taken as an experimental confirmation of the parton model [2] , and the observation in 1979 of a third jet in e + e − collisions at 17ü30 GeV has been recognized [3] as the first experimental evidence of the gluon [4] . These jets, being directly observable in experiments as jets of particles, will be called "visible jets" in the following. Theoretically, the transition between perturbative and non-perturbative QCD is at a scale Q 0
doi:10.1360/03yg9035 fatcat:l54zqvnayneo5cpbs2ibmwpdum