Spin observables in with a transverse initial state polarization

Abstract

The formalism describing the scattering of two spin-1 2 objects is reviewed for the case ofpp →ΛΛ. It is shown that an experiment utilizing a transverse target polarization can, in principle, completely determine the spin structure of the reaction. Additional measurements, even those using both beam and target polarizations, would not be sensitive to any additional spin dynamics. Thus, the transverse target polarization allows access to the complete set of spin observables, not just the subset upon which the literature has previously focused. This discussion is especially relevant in light of the data collected by PS185/3 at LEAR.Exclusive production of antihyperon-hyperon states from antiproton-proton annihilation (pp → Y Y ) has been extensively studied near threshold by the PS185 collaboration throughout the 13 year lifetime of LEAR at CERN [1,2]. Results for the total and differential cross-sections and those spin observables depending only on final state spins have been published for a range of energies and channels. In 1996, an upgraded version of the experiment, PS185/3, incorporated a transverse target polarization to allow sensitivity to a wider range of spin observables in the reactionpp →ΛΛ [3].There is significant interest in the results of this measurement. Two types of models with different physical motivations have been successfully used to describe the reaction in this energy regime: K and K * meson exchange [4,5] and effective quark models [6,7]. While careful applications of each of these approaches have been able to describe the existing data with reasonable accuracy, differing predictions are obtained for those observables which depend on initial state spin [4,6]. There has also been growing interest in the relevance of the spin structure ofpp →ΛΛ to the question of the strangeness component of the nucleon [8,9].The formalism for scattering two spin-1 2 particles to two spin-1 2 particles has been well developed in both the general case and in application to thepp →Ȳ Y reaction [10][11][12][13]. The implications of this application of the formalism must be carefully explored for the larger set of observables available to PS185/3 [14,15]. The recent literature discussing the strangeness production dynamics has focused on the depolarization D nn , and, to a lesser extent, other rank-2 spin observables to which PS185/3 is directly sensitive [3,4,6,8,14]. As will be shown below, the use of a transverse target polarization, in principle, allows the complete determination of the spin structure of the reaction. This then permits model independent predictions of the full set of spin observables, including those that were not directly measured. This is the first demonstration of the feasibility of such an analysis for pp →ΛΛ, although this possibility had been hinted at by previous publications [13].In discussing spin-1 2 particle scattering it is common to parameterize the spin structure of the transition matrix M explicitly. Forpp →ΛΛ, the transition matrix M can be written 1

Spin physics with antiprotons

“…It was demonstrated [33] that the use of a transversely polarised target, in principle, allows the complete determination of the spin structure of the reaction. Corresponding measurements was performed by PS185 Collaboration, see [34] and references therein.…”

Experimental determination of the complete spin structure forp¯p→Λ¯ΛatFields1, Paschke2, Quinn3 et al. 2006Phys. Rev. C230100View full textAdd to dashboardCite

“…As described above, it has been shown [12] that this greatly expands the accessible spin information. The target itself was a solid 9 mm long, 6 mm diameter cylinder of frozen Butanol (C 4 H 9 OH) doped with TEMPO (C 9 H 18 NO) [21].…”

“…The third column gives the indicated correlation (multiplied by I0) in terms of the parameters of the spin-scattering matrix given in Eq. (12). The second column lists alternate names for the spin correlations.…”

“…It was also noted [12] that such data contained enough information to permit determination of not just a few observables but the entire spin-structure of the reaction. From this, all possible spin observables could then be determined.…”

Spin observables and spin structure functions: Inequalities and dynamics

“…We follow here the notation adopted in the recent literature. See, for example [98][99][100]. The amplitude is denoted Figure 10: Some of the results of PS 185 [94] for the analysing power, depolarisation and transfer of polarisation of the reactionpp → ΛΛ at p lab = 1.637 GeV/c.…”