Off-diagonal helicity density matrix elements for heavy vector mesons inclusively produced in N-N, gamma-N, l-N interactions

Final state interactions in quark fragmentation may give origin to non zero values of the off-diagonal element rho_(1,-1) of the helicity density matrix of vector mesons V produced in current jets, with a large energy fraction x_E; the value of rho_(1,-1)(V) is related to the hard constituent dynamics and tests unusual properties of it. Some recent data on phi, K^* and D^* produced in e^+ e^- annihilations at LEP show such effects. Predictions are given here for rho_(1,-1) of heavy mesons produced in nucleon-nucleon, gamma-nucleon and lepton-nucleon interactions.Comment: LaTeX, 10 pages, 1 postscript figure, uses epsfig.sty. Revised version, to be published on Phys. Lett. B. Some statements added to clarify tex

Spin effects in the fragmentation of a transversely polarized quark

An azimuthal dependence of pions produced in polarized Deep Inelastic Scattering, gamma^* - p(transv. polarized) -> pion + X, has been recently observed and might be related to the so-called Collins effect. We discuss in details, for a general spin configuration of the nucleon, the kinematics of the process and methods of extracting information on the fragmentation properties of a polarized quark. Assuming that the observed azimuthal dependence is indeed due to Collins effect, we derive a lower bound estimate for the size of the quark analysing power, which turns out to be large.Comment: 18+1 pages, LaTeX, 5 eps figures, uses epsfig.sty; v2: Some technical problems in dimensions of Figs. 2 and 3 remove

An Interesting Charmonium State Formation and Decay : ppˉ→1D2→1P1γp \bar p \to ^1D_2 \to ^1P_1 \gamma

Massless perturbative QCD forbids, at leading order, the exclusive annihilation of proton-antiproton into some charmonium states, which, however, have been observed in the $p\bar p$ channel, indicating the significance of higher order and non perturbative effects in the few GeV energy region. The most well known cases are those of the $^1S_0$ ($\eta_c$) and the $^1P_1$. The case of the $^1D_2$ is considered here and a way of detecting such a state through its typical angular distribution in the radiative decay $^1D_2 \to$ $^1P_1 \gamma$ is suggested. Estimates of the branching ratio $BR(^1D_2 \to p\bar p)$, as given by a quark-diquark model of the nucleon, mass corrections and an instanton induced process are presented.Comment: 9 pages (no figures), Plain TeX, CBPF-NF-014/94, INFNCA-TH-94-

Single transverse spin asymmetries in inclusive hadron production

A consistent phenomenological approach to the computation of transverse single spin asymmetries in inclusive hadron production is presented, based on the assumed generalization of the QCD factorization theorem to the case in which quark intrinsic motion is taken into account. New k_T and spin dependent quark distribution and fragmentation functions are considered: some of them are fixed by fitting data on p(transv. polarized) + p -> pion + X and predictions are given for single spin asymmetries in l + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X processes.Comment: LaTeX, 3 pages, 2 eps figures, uses epsfig.sty, fleqn.sty, npb.sty. Talk delivered by M. Anselmino at the 7th International Workshop on Deep Inelastic Scattering and QCD (DIS99), Zeuthen, April 1999, to appear in Nucl. Phys. B (Proc. Suppl.

Single Spin Asymmetry in Inclusive Pion Production

It is shown how the single spin asymmetry observed in inclusive pion production is related, in the helicity basis, to the imaginary part of the product of two different distribution amplitudes, rather than to the usual quark and gluon distribution functions; there is then no reason why it should be zero even in massless perturbative QCD, provided the quark intrinsic motion is taken into account. A simple model is constructed which reproduces the main features of the data.Comment: (To appear in the proceedings of the XI International Symposium on High Energy Spin Physics, September 15-22, Bloomington, Indiana). 5 pages + 1 figure, LaTeX 2.09, report DFTT47/94, INFNCA-TH-94-21. (figure appended as uuencoded, tar-compressed postscript file; uncompressed ps file available under request from [email protected]

Constraints on Gluon Sivers Distribution from RHIC Results

We consider the recent RHIC data on the transverse single spin asymmetry (SSA) A_N, measured in p(transv. polarized) p --> pion X processes at mid-rapidity by the PHENIX Collaboration. We analyze this experimental information within a hard scattering approach based on a generalized QCD factorization scheme, with unintegrated, transverse momentum dependent (TMD), parton distribution and fragmentation functions. In this kinematical region, only the gluon Sivers effect could give a large contribution to A_N; its vanishing value is thus used to give approximate upper limits on the gluon Sivers function (GSF). Additional constraints from the Burkardt sum rule for the Sivers distributions are also discussed.Comment: LaTeX 2e, 4 pages, 2 ps figures, uses aipproc.cls. Talk delivered by U. D'Alesio at the "17th International Spin Physics Symposium", SPIN2006, October 2-7, 2006, Kyoto, Japa