11 research outputs found
Spin observables in antiproton-proton to AntiLambda-Lambda and density-matrix constraints
The positivity conditions of the spin density matrix constrain the spin
observables of the reaction antiproton-proton to AntiLambda-Lambda, leading to
model-independent, non-trivial inequalities. The formalism is briefly presented
and examples of inequalities are provided.Comment: 4 pages, Latex with included AIP style, Contribution to LEAP 05, to
appear in the Proceeding
Constraints on spin observables
Positivity constrains the allowed domain for sets of spin observables in
exclusive or inclusive reactions. Examples are given for strangeness-echange
reactions and photoproduction.Comment: 4 pages, to appear in the Proc. QCD08, MOntpellier, France, July
2008, ed. S. Nariso
Spin observables and spin structure functions: inequalities and dynamics
Model-independent identities and inequalities relating the various spin
observables of a reaction are reviewed in a unified formalism, together with
their implications for dynamical models, their physical interpretation, and the
quantum aspects of the information carried by spins, in particular
entanglement. These constraints between observables can be obtained from the
explicit expression of the observables in terms of a set of amplitudes, a
non-trivial algebraic exercise which can be preceded by numerical simulation
with randomly chosen amplitudes, from anticommutation relations, or from the
requirement that any polarisation vector is less than unity. The most powerful
tool is the positivity of the density matrices describing the reaction or its
crossed channels, with a projection to single out correlations between two or
three observables. For the exclusive reactions, the cases of the
strangeness-exchange proton-antiproton scattering and the photoproduction of
pseudoscalar mesons are treated in some detail: all triples of observables are
constrained, and new results are presented for the allowed domains. The
positivity constraints for total cross-sections and single-particle inclusive
reactions are reviewed, with application to spin-dependent structure functions
and parton distributions. The corresponding inequalities are shown to be
preserved by the evolution equations of QCD.Comment: 135 pages, 37 figures, pdflatex, to appear in Physics Reports, new
subsections added, typos corrected, references adde
Model-independent constraints on spin observables
We discuss model-independent constraints on spin observables in exclusive and
inclusive reactions, with special attention to the case of photoproduction.Comment: 6 pages, 5 figures, Talk by J.-M. Richard at NSTAR 2009, IHEP,
Beijing (China), April 19-22, 2009, Proc. to appear in "Chinese Physics C
Constraints on spin observables in antiproton-proton to antiLambda-Lambda
It is recalled that spin-observables in the strangeness-exchange reaction
are not independent but are related to
each other by simple algebraic relations. This provides constraints on the
existing data on polarization and spin-correlation coefficients, and also on
the forthcoming data obtained using a polarized proton target.Comment: RevTex, 9 page