Including Cahn and Sivers effects into event generators

It is demonstrated that event generators LEPTO and PYTHIA can be modified to describe some azimuthal modulations. The comparisons of results obtained with modified LEPTO with existing data in the current fragmentation region of SIDIS are presented for Cahn and Sivers effects as well as the predictions for the target fragmentation region. The predictions for Sivers effect in the Drell--Yan process obtained with modified PYTHIA are also presented. The concept of hadronization function is discussed.Comment: Presented at Transversity 2005 workshop, September 7-10, Como, Italy. 8 pages. Word Scientific Proceedings style (included

Beyond Collins and Sivers: further measurements of the target transverse spin-dependent azimuthal asymmetries in semi-inclusive DIS from COMPASS

In semi-inclusive DIS of polarized leptons on a transversely polarized target eight azimuthal modulations appear in the cross-section. Within QCD parton model four azimuthal asymmetries can be interpreted at leading order, two of them being the already measured Collins and Sivers asymmetries. The other two leading twist asymmetries, related to different transverse momentum dependent quark distribution functions, and also additional four asymmetries which can be interpreted as twist-three contributions have been measured for the first time at COMPASS, using a 160 GeV/c longitudinally polarized ($P_{beam}\simeq -0.8$) muon beam and a transversely polarized $^6LiD$ target. We present here the preliminary results from the 2002-2004 data.Comment: Talk given on XV Internetional Workshop on Deep-Inelastic Scattering and Related Subjects, April 16-20, 2007, Munich, German

Double spin azimuthal asymmetries A_{LT} and A_{LL} in semi-inclusive DIS

Within the LO QCD parton model of SIDIS with unintegrated quark distribution and fragmentation functions we study the transverse momentum and azimuthal dependencies of the double spin asymmetries $A_{LT}$ and $A_{LL}$. For later we include ${\cal O}(k_{\perp}/Q)$ kinematic corrections, which induce an azimuthal modulation of the asymmetry, analogous to the Cahn effect in unpolarized SIDIS. We show that a study of these asymmetries allows to extract the transverse momentum dependence of the unintegrated helicity distribution function $g_{1L}^q(x,k_\perp)$ and $g_{1T}^q(x,k_\perp)$. This report is based on research published in [1] and [2], where predictions are given for ongoing COMPASS, HERMES and JLab experiments.Comment: 4 pages, 2 figures. Talk presented at the 17th International Spin Physics Symposium, SPIN2006, Kyoto, Japan, October 2-7, 200

Double hadron lepto-production in the current and target fragmentation regions

We study the inclusive production of two hadrons in deep inelastic processes, l N ---> l h_1 h_2 X, with h_1 in the current fragmentation region (CFR) and h_2 in the target fragmentation region (TFR). Assuming a factorized scheme, the recently introduced polarized and transverse momentum dependent fracture functions couple to the transverse momentum dependent fragmentation functions. This allows the full exploration of the fracture functions for transversely polarized quarks. Some particular cases are considered.Comment: 14 pages, 2 figure

The Proton Spin Puzzle and Λ\Lambda Polarization in Deep--Inelastic Scattering

We point out that measurements of longitudinal $\Lambda$ polarization in the target fragmentation region of deep--inelastic $\nu \,N$ and $\mu \,N$ or $e \, N$ scattering may test dynamical mechanisms invoked to explain the proton spin puzzle. A previously-proposed model for polarized $\bar s s$ pairs in the proton wave function reproduces successfully the negative $\Lambda$ polarization found in the WA59 $\bar \nu \, N$ experiment, and makes predictions that could be tested in future $\mu \, N$ and $e \, N$ experiments.Comment: 16 pages, LaTeX, 9 eps figures uuencoded in separate file, typographical errors correcte

SIDIS in the target fragmentation region: polarized and transverse momentum dependent fracture functions

The target fragmentation region of semi-inclusive deep inelastic scattering is described at leading twist, taking beam and target polarizations into account. The formalism of polarized and transverse-momentum dependent fracture functions is developed and the observables for some specific processes are presented.Comment: 18 pages, 2 figures. Some equations modified and text shortened; main conclusions unchange

Lambda and Lambda-bar Polarization in Lepton Induced Processes

The study of the longitudinal polarization of Lambda and Lambda-bar hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z0 decays allows to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Lambda and Lambda-bar longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will provide soon accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms.Comment: 17 pages, LaTex with epsfig.sty, including 10 figures One reference adde