Study of quark fragmentation ine+e−annihilation at 29 GeV: Global jet parameters and single-particle distributions

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Abstract

In this paper, results are presented from a study of the hadronic final states in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ annihilation at 29 GeV. The data were obtained with the High Resolution Spectrometer (HRS) at the SLAC PEP ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ colliding-beam facility. The results are based on 6342 selected events corresponding to an integrated luminosity of 19.6 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$. The distributions of the events in sphericity (S), thrust (T), and aplanarity (A) are given and compared to other ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ data in the same energy range. We measure 〈S〉=0.130\ifmmode\pm\else\textpm\fi{}0.003\ifmmode\pm\else\textpm\fi{}0.010 and 〈1-T〉=0.100\ifmmode\pm\else\textpm\fi{}0.002. The sphericity distribution is compared to sphericity measurements made for beam jets in hadronic collisions as well as jets studied in neutrino scattering. The data sample is further reduced to 4371 events with the two-jet selections, S\ensuremath{\le}0.25 and A\ensuremath{\le}0.1. The single-particle distributions in the longitudinal and transverse directions are given. For low values of the momentum fraction (z=2p/W), the invariant distribution shows a maximum at z\ensuremath{\sim}0.06, consistent with a QCD expectation. The data at high Feynman x (${\mathit{x}}_{\mathit{F}}$) show distribution consistent with being dominated by a (1-${\mathit{x}}_{\mathit{f}}$${)}^{2}$ variation for the leading quark-meson transition. The rapidity distribution shows a shallow central minimum with a height (1/${\mathit{N}}_{\mathrm{ev}}$${\mathit{dN}}^{\mathrm{h}}$/dY${\mathrm{\ensuremath{\Vert}}}_{\mathrm{Y}=0}$=2.3\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.07. The mean charged multiplicity is measured to be 〈${\mathit{n}}_{\mathrm{ch}}$〉=13.1\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.6. The mean transverse momentum relative to the thrust axis 〈${\mathit{p}}_{\mathit{T}}$〉 rises as a function of z to a value of 0.70\ifmmode\pm\else\textpm\fi{}0.02 GeV/c for z\ensuremath{\gtrsim}0.3. The distributions are compared to those measured in other reactions.

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