Lambda polarization in unpolarized hadron reactions

The transverse polarization observed in the inclusive production of Λ hyperons in the high energy collisions of unpolarized hadrons is tackled by considering a new set of spin and k _⊥ dependent quark fragmentation functions. Simple phenomenological expressions for these new “polarizing fragmentation functions” are obtained by a fit of the data on Λ's and \(\bar \Lambda \)'s produced in p?N processes.     

Diquarks in exclusive reactions at large momentum transfer

Following many theoretical and experimental indications we assume that diquarks, in certain intermediate energy regions, can act as quasi-elementary constituents and take part in large momentum transfer reactions. We apply the idea to large angle exclusive interactions and show that diquarks could explain the whole amount of intriguing polarisation data in proton-proton elastic scattering and πp→?p reactions. The behaviour of the electromagnetic form factors of the nucleon is also discussed in the diquark model.     

Off-diagonal helicity density matrix elements for vector mesons produced at LEP

Final state interactions may give origin to non-zero values of the off-diagonal element of the helicity density matrix of vector mesons produced in annihilations, as confirmed by recent OPAL data on and 's. Predictions are given for of several mesons produced at large and small , i.e. collinear with the parent jet; the values obtained for and are in agreement with data. The fragmentation functions of quarks and gluons into photons are studied beyond the Leading Logarithm approximation. We address the nature of the initial conditions of the evolution equation solutions and study problems related to factorization scheme invariance. The possibility of measuring these distributions in LEP experiments is discussed, and a comparison with existing data is made. Received: 15 May 1997 / Published online: 20 February 1998     

A possible mechanism for spin effects in large anglep−p elastic scattering

We propose a simple parton model interpretation of large anglep?p elastic scattering in terms of elementaryq?q scattering. We formulate the model and give some numerical estimates which qualitatively explain the most important spin effects. We do not assume any particular quark recombination mechanism but we stress the importance of the proton wave function. Comparisons with other models are made.