Nils A. Tornqvist

Jet handedness as a measure of quark and gluon polarization

Abstract We introduce a new concept, the handedness of a jet, which can be used to determine the polarization of a high-energy quark or gluon produced in a hard collision. The method can be tested in e + e - → 2 jets at the Z 0 peak where the polarization of the emerging quarks is known and correlation between jet handedness and parton polarization could be determined. Subsequently, this correlation could be used in other contexts to determine the parton polarization from a measurement of jet handedness. In particular, the method could be very useful for measuring quark and gluon polarization and the quark “transversity” distribution in the proton.

Application of the generalized Veneziano model to K−p → π−π+Λ

Abstract The five-point function in the generalized Veneziano model is used for a phenomenological description of the process K−p → π−π+Λ. With essentially only one free parameter this model reproduces the main features of the experimental data including both resonance production and Regge behaviour, in the energy range 3–10 GeV/c.

A crossing-symmetric description of data with the generalized Veneziano model

The generalized Veneziano model is applied to study the reactions: n(A) K+p → Koπ+p n, n(B) K−p → Koπ−p n, n(C) K−p → Koπ−p n, which are related by crossing. It is found that with the same formula and essentially only one free parameter, one is able to give a good global description of all three reactions at energies ranging from 2.5 to 13 GeV. The possibility of extending the study to further reactions is also briefly considered.

Is isospin invariance violated in πN backward scattering

Abstract Isospin invariance implies an inequality for πN cross sections. We point out that, if the low-energy charge exchange experiments are taken literally, they seem to show widespread violation of this inequality in πN backward scattering.

Crossing K−p → π−π+Λ into π+p → K+π+Λ using the generalized veneziano model

Abstract The dual multiparticle model for K − p → π − π + △ suggested by Petersson and the present author is applied to the crossed reaction π + p → π t - π + △. We avoid the complication due to pomeron exchange by limiting ourselves mainly to the dominant subprocess π + p → K + Y ∗+ (1385) . The model predicts correctly the energy dependence and differential cross sections and even the normalizing parameter within a factor of two. An alternative model suggested by the Harari-Rosner rules fails to give a good fit to the differential cross sections.

On the handedness in polarized τ → a1ν → 3πν decay

Abstract We discuss the polarization assymetries in the reactions e + e − → τ + τ − and τ → a 1 ν τ → 3 πν τ at the Z 0 . The a 1 → 3 π decay is particularly interesting since it is the lightest hadronic decay in which the helicity of the initial state can be determined from the distribution of the final particle momenta. Thus it is the first example of a helicity self-analysing strong decay, as Λ → N π is for weak decays. The relevant observable is the “handedness” asymmetry introduced earlier. It can be used together with two other asymmetries to determine both polarization of τ and left-handedness of ν τ , and to check the self-consistency of the analysis.

A method for the determination of the spin and parity of a resonance through spin-rotation parameter measurements

A simple graphical method for studying polarization phenomena is presented. It provides a new method for the determination of the spin and parity of a resonance formed in the reactions πN → πN, πN → KΛ(Σ), KN → KN KN → → π Λ(Σ). This method of spin-parity determination requires measurements of spin-rotation parameters, and is based on the observation that the spin and parity of the dominating partial wave are simply related to the number of times and the direction the final polarization vector rotates, when the scattering angle is varied from 0 to 180°. This spin-parity determination would be independent of corresponding determinations using angular distributions. Apart from the spin-parity determination, the graphical technique is useful for a compact description of spin effects in terms of directly observable quantities. The method is applied and tested by plotting predictions of πN → πN phase-shift analysis.