Two-Jet Hadroproduction as a Measure of the Gluon at Small X
We investigate the proposal of the CDF collaboration that same-side two-jet production in $p\bar{p}$ collisions may be used to determine the gluon distribution at small $x$.
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arXiv subjects
R. G. Roberts
Publications and source records attributed to R. G. Roberts.
Consistent Analysis of the Spin Content of the Nucleon
The recent measurements of lepton nucleon scattering with polarised neutron and deuteron targets are analysed together with the previous polarised proton data in a mutually consistent way. The detailed $x$-dependence of the polarisation asymmetry in the valence region is shown to be in agreement with historical predictions based on quark models. The Bjorken sum rule is shown to be confirmed at the $1σ$ level and estimates of the spin content of the nucleon $Δq$ are extracted. While the average value of $Δq$ from the three experiments comes out to be $0.41\pm0.05$ (to be compared with the naive quark model theoretical expectation of 0.58) this experimental average value is more than one standard deviation from the value obtained from any individual experiment.This inconsistency can be overcome by allowing arbitrary higher twist contributions but the resulting precision is poor, $Δq = 0.38\pm 0.48$.
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Light gluinos in high-Q2 deep inelastic scattering
A slight incompatibility in recent low-energy and high-energy α_s measurements can be interpreted as evidence for new light colour degrees of freedom. Assuming that these are the gluinos of a supersymmetric extension of the Standard Model, we investigate to what extent they change the standard QCD predictions for deep inelastic structure functions, and in particular whether thay can be detected in such measurements at HERA. We present a modified set of parton distributions which includes a light gluino distribution and which can be used for further phenomenological investigations.
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Stitching the Yukawa Quilt
We develop a systematic analysis of quark mass matrices which, starting with the measured values of quark masses and mixing angles, allows for a model independent search for all possible (symmetric or hermitian) mass matrices having texture zeroes at the unification scale. A survey of all six and five texture zero structures yields a total of five possible solutions which may be distinguished by improved measurements of the CKM matrix elements and which may readily be extended to include lepton masses with the Georgi-Jarlskog texture. The solutions naturally suggest a parameterisation for the mass matrices based on a perturbative expansion and we present some speculations concerning the origin of such structure.
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Phenomenological constraints on the flavour asymmetry of the nucleon sea
We study the possible flavour asymmetry, $\bar{u} \neq \bar{d}$, of the light quark sea distributions of the proton. We discuss the information that is at present available from data on deep-inelastic lepton-nucleon scattering and from Drell-Yan production on various nuclear targets. We show that the ratio of dilepton yields on hydrogen and deuterium targets is very sensitive to $\bar{u}-\bar{d}$.
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Implications for Minimal Supersymmetry from Grand Unification and the Neutralino Relic Abundance
We examine various predictions of the minimal supersymmetric standard model coupled to minimal supergravity. The model is characterised by a small set of parameters at the unification scale. The supersymmetric particle spectrum at low energy and the spontaneous breaking of the standard model itself are then generated radiatively. The previously considered predictions of the model now include the neutralino relic density which in turn provides bounds on the scale parameters. We find a remarkable consistency among several different constraints which imply all supersymmetric particle masses preferably within the reach of future supercolliders (LHC and SSC). The requirement that the neutralino be the dominant component of (dark) matter in the flat Universe provides a {\em lower} bound on the spectrum of supersymmetric particles beyond the reach of LEP, and most likely also the Tevatron and LEP 200.
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