986 research outputs found

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

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    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

    An Interesting Charmonium State Formation and Decay : ppˉ1D21P1γp \bar p \to ^1D_2 \to ^1P_1 \gamma

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    Massless perturbative QCD forbids, at leading order, the exclusive annihilation of proton-antiproton into some charmonium states, which, however, have been observed in the ppˉp\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 1S0^1S_0 (ηc\eta_c) and the 1P1^1P_1. The case of the 1D2^1D_2 is considered here and a way of detecting such a state through its typical angular distribution in the radiative decay 1D2^1D_2 \to 1P1γ^1P_1 \gamma is suggested. Estimates of the branching ratio BR(1D2ppˉ)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-

    A strategy towards the extraction of the Sivers function with TMD evolution

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    The QCD evolution of the unpolarized Transverse Momentum Dependent (TMD) distribution functions and of the Sivers functions have been discussed in recent papers. Following such results we reconsider previous extractions of the Sivers functions from semi-inclusive deep inelastic scattering data and propose a simple strategy which allows to take into account the Q^2 dependence of the TMDs in comparison with experimental findings. A clear evidence of the phenomenological success of the TMD evolution equations is given, mostly, by the newest COMPASS data off a transversely polarized proton target.Comment: 15 pages, 7 figures, 2 table

    1P1^1P_1 charmonium state decay into ppˉp \bar p in QCD models including constituent quark mass corrections

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    Stimulated by the experimental observation, made by the E760 Collaboration at Fermilab, of the 1 ⁣P1^1\!P_1 state of charmonium resonantly formed in ppˉp\,\bar p annihilation, we perform a calculation of the decay width for the 1 ⁣P1ppˉ^1\!P_1\to p\,\bar p process. To this end, we employ a phenomenological model which adds constituent quark mass corrections to the usual massless QCD models for exclusive processes. For massless models, in fact, the process under consideration is forbidden by the so-called helicity selection rules, while it is allowed in our extended model. We find Γ(1 ⁣P1ppˉ)\Gamma(^1\!P_1\to p\,\bar p) to be in the range 1101-10 eV. We also compare our results with previous, indirect estimates, based on QCD multipole expansion models.Comment: 17 pages, REVTeX 3.0, 1 postscript figure included. Revised version, to be published in Physical Review D. Brief discussion of the role of other nonperturbative effects and three references added in the introduction; Comparison with QCD multipole expansion model slightly reformulated; Some sentences added in the conclusions; Results unchange

    New proton polarized structure functions in charged current processes at HERA

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    Estimates for longitudinal spin asymmetries which single out new polarized nucleon structure functions in deeply inelastic charged current interactions at HERA energies are given, exploiting their interpretation in terms of polarized quark distributions. These asymmetries turn out to be large and allow a measurement of the new polarized structure functions g1Wg_1^{W} and g5Wg_5^{W}, which would add valuable tests and information on the spin content of quarks inside a polarized proton. We also show that single spin asymmetries in neutral current interactions are very small.Comment: LaTeX, 8 pages, 6 figure

    Single transverse spin asymmetries in inclusive hadron production

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    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.

    Phenomenology of Sivers Effect with TMD Evolution

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    Following the TMD evolution scheme recently proposed for the unpolarized and the Sivers distribution function, we propose a simple strategy to take into account this TMD Q^2 dependence in our phenomenological extraction of the Sivers function from SIDIS data. New results are presented and possible future applications are discussed.Comment: Contribution to the Proceedings of the XX International Workshop on Deep-Inelastic Scattering and related subjects (DIS2012), 26-30 March 2012, Bonn, Germany. One figure correcte
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