arXiv subjects
Publications and source records attributed to Paolo M. Gensini.
Rapidly convergent, unsubtracted dispersion relations have been used to test coupled channel analyses of low-energy S = -1 meson-baryon pi Y --> pi Y' channels. We conclude that the low-energy S = -1 meson-baryon sector is less well known than currently believed, and that it deserves more accurate experiments and analyses.
Expanded and updated version of a talk originally presented at ``IVth Int. Symp. on Pion--Nucleon Physics and the Structure of the Nucleon'', Bad Honnef, 9--13 September 1991, originally published in $πN$ Newletter 6 (1992) 21--32. Table of contents: 1. Introduction. 2. $σ$--terms and ``measurements'' of the strange--quark scalar density of the nucleon. 3. Methods of extrapolation to $q^2 = t = ω^2 = 0$: a subjective review: 3.1. The ``improved'' Altarelli--Cabibbo--Maiani method. 3.2. The Fubini--Furlan analysis of meson-nucleus scattering lengths. 3.2. The ``unitarized'' version of the Cheng--Dashen theorem. 4. Capabilities for a $\bar{K}N$--scattering experiment at DA$Φ$NE. 5. ``Envoi''.
The dispersive determination of $π{Y}Σ$ coupling constants ($Y = Λ, Σ$) and the implications for low-energy $\bar{K}N$ analysis are discussed. (Presented by G. Violini at the "7th Int. Symp. on Meson-Nucleon Physics and the Structure of the Nucleon, MENU '97", Vancouver, B.C., July 28th - August 1st, 1977).
We delineate a ``theoretical'' $χ^2$--functional technique to implement fixed--$t$ analyticity on the invariant amplitudes for the $\bar{K}N$, $πΛ$, $πΣ$ coupled channels in a fast and straightforward way.
The data from the last seven experiments performed on polarized deep--inelastic scattering on proton and neutron (or deuteron) targets have been analyzed in search of a precise determination of the spin fraction carried by the quarks in the nucleon. We find that this fraction can be of the size expected from na\"ıve quark model arguments, provided the gluon axial anomaly is explicitly included and the isosinglet axial charge normalization is fixed at a suitably low momentum scale, such that a) the running, strong coupling constant is about unit, and b) the orbital angular momentum inside the nucleon vanishes. We also find that, despite the appeal of this solution of the ``nucleon spin crisis'', a solution where the axial anomaly is absent and its effects are traded for an appreciable strange quark polarization can not however be excluded --- because of the limited accuracy of the data --- unless this latter and/or the gluon polarization in the nucleon are explicitly measured.
We present in this contribution the basic formulæ for the analysis of low--momentum charged-- and neutral--kaon interactions in hydrogen, including as well a (brief) description of the problems left open by past experiments, and of the improvements DA$Φ$NE can be expected to offer over them. Interactions in deuterium and other light nuclei will be only briefly mentioned, and only in those respects touching directly upon the more ``elementary'' aspects of kaon--nucleon interactions.
The present talk summarises the 1993 situation in understanding the spin structure of the nucleon via electron and muon polarised deep--inelastic scattering (PDIS). The central question I shall address here is if the data can be interpreted as evidence for polarisation in the ``strange'' nucleon ``sea'', and I conclude that they can not: incidentally, I also find that they can not be constructed as evidence for violation of perturbative QCD (PQCD), either. Talk presented at ``Quinto Convegno su Problemi di Fisica Nucleare Teorica'', Cortona (Arezzo, Italy), October 1993. To be published in the proceedings: ``Perspectives on Theoretical Nuclear Physics (V)'', L. Bracci, et al., eds. (ETS Ed., Pisa 1994)
Present evidence on baryon axial--vector couplings is reviewed, the main emphasis being on internal consistency between asymmetry and rate data. A complete account of all {\sl small} terms in the Standard Model description of these latter leads to {\sl both} consistency {\sl and} evidence for breaking of flavour SU(3) in the axial couplings of octet baryons. Talk presented at "5th Int. Sympos. on Meson--Nucleon Physics and the Structure of the Nucleon", Boulder, CO, sept. 1993. To be published in $πN$ Newsletter.
We survey the open problems in low--energy $KN$ physics, in the perspective of using the new machines presently planned, such as the $ϕ$--factory DA$Φ$NE at I.N.F.N. Nat. Labs. in Frascati (as a source of {\sl tagged}, low--energy kaons) and the KAON Factory at TRIUMF (as a producer of intense, intermediate--energy kaon beams).
The paper is the written version of a talk presented at the "VIIth Winter School of Hadronic Physics", held in Folgaria (Trento), Italy, February 10--15, 1992. We intend to illustrate in this lecture the possibilities opening up at machines planned for the nineties for low--energy kaon--nucleon interactions, keeping the focus on the theoretical problems they should help to solve. We shall deal here only with the $ϕ$--factory DA$Φ$NE$^1$ and consider, for brevity, interactions with light, gaseous targets, using gaseous $H_2$ as a benchmark for which to estimate the rates to be expected in a typical apparatus.
A chapter to be included in "The DA$\mitΦ$NE Physics Handbook" by the DA$Φ$NE Theory Working Group, this paper covers the phenomenology of low--energy $K N$ physics, with particular emphasis on the problems still to be solved by a careful experimental investigation and on the theoretical tools to analyse it.