1,721,024 research outputs found
Theory of the EMC effect
No full textWe present a theory of the well-known EMC effect based on the idea that the dynamics of the nucleus is coherent and leads to a lowering of the effective nucleon mass by about 60 MeV. We further show that the so-called shadowing effect can be explained via a single-diffractive mechanism for the small-χB region which is interfered upon by the Pauli exclusion principle
Nuclear models and the hypernuclear interaction
No full textWe present a first calculation of the potential and spin-orbit coupling for hypernuclei in the framework of a nuclear-potential model based on a spontaneous collective (superradiant) pion-nucleon-delta interaction. A perturbative evaluation of the propagation of a hyperon in such a coherent medium leads to an effective hypernuclear potential of the same shape and roughly half the depth (i.e -30 MeV) of the standard nuclear potential and a negligible spin-orbit coupling for both Lambda and Sigma hypernuclei. Such results are in complete agreement with existing experimental data. Moreover, in this framework, we are able to explain the surprisingly narrow decay widths of the Sigma hypernuclei
A simple explanation of hyperon polarization at high pt
No full textWe present the first truly dynamical calculation of the single transverse-spin asymmetry for the process pN --> B(up) + X, where B is LAMBDA0 or SIGMA0,+/- observed at large angles. After showing that the trip le-Regge model gives a good representation of the inclusive unpolarized cross sections, the polarization is calculated by considering the hyperon to emerge in the final state either directly or as the result of virtual dissociation of a parent baryon. Our results reproduce very well both the measured p(T) and x(F) dependence of the hyperon polarization
The strangeness content of the proton can only be small
No full textIt has recently been claimed that the explicit introduction of a so-called "non-perturbative" contribution to the spin-dependent strange-quark distribution in the proton sea may avoid positivity bounds obtained from very precise data presently available for the corresponding unpolarised distributions. We show that the unusual large-xB behaviour, ∼(1 - x)^5, required for such avoidance is entirely incompatible with that displayed by the existing deep-inelastic neutrino data, ∼(1 - x)^10. Thus we demonstrate the untenability of this scenario for the avoidance of the positivity bound on the magnitude of the strange-quark contribution to the proton-spin sum-rule. Such a bound leads to a marked disagreement between predictions based on the light-cone expansion in perturbative QCD and experimental measurements
Polarized Strange Quarks in the Proton and the Validity of Quantum Chromodynamics - Comment
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