Multijet structure in quantum chromodynamics
Choy Heng Lai1980, Nuclear Physics B
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Abstract
Field theories naturally give rise to multiple jets of hadrons in short-distance processes, such as e+e -annihilation. In particular, a low-energy jet of hadrons distributed in some cone of opening angle 6 would be naively expected to evolve at high energies into multiple jets within the angle 6. We explore to what extent this will happen in quantum chromodynamics. * Permanent address. ** Jet opening angles decrease very roughly as Nhadrons/Eje t. * To ensure that the quanta are made at short distances we think of Ej~ t -~ ~/~ (in e + e-) or Ejet = (PT)jet (in pp---~high-pT jets ). ** Extracted from the work of Polyakov [4]. (This proliferation can be nicely interpreted as a branching process [5] .) It is by now common wisdom that this conjectural picture should in some way apply to QCD. *** We will not discuss the case where one observes some' fixed number of jets at large fixed angles to one another. The probability of such a configuration vanishes roughly as a power of 1/In E. * We always measure p2 in units of A2~ (1 GeV)2. In this section we ignore the difference between q--* qG and G--* GG. The picture does not warrant any better. ** For reasons of symmetry we assume that each breakup is into two partons of essentially equal p2. * The azimuthal angle of the partons is entirely random. ** We choose a u-quark jet for all partons. This should be acceptable, as we are interested in calorimetric properties, not flavor. * Quantities such as (p~-Had), which are not linear as is (45), are probably more sensitive to perturbative broadening.
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