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Register a new userInclusive production of hadrons in $ell^uparrow p^uparrow to h^uparrow X$ and spin measurements
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Authors
M. Anselmino
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We discuss the production of polarized hadrons in polarized lepton nucleon interactions and show that the helicity density matrix of the hadron, when measurable, can give information on the spin structure of the nucleon and the spin dependence of the quark fragmentation process. Single spin asymmetries in the $ell N^uparrow to hX$ process are also briefly discussed.
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We present a study of transverse single-spin asymmetries (SSAs) in $p^uparrow pto J/psi,X$ and $p^uparrow pto D X$ within the framework of the generalized parton model (GPM), which includes both spin and transverse momentum effects, and show how they can provide useful information on the still almost unknown gluon Sivers function. Moreover, by adopting a modified version of this model, named color gauge invariant (CGI) GPM, we analyze the impact of the initial- and final-state interactions on our predictions. As a consequence, we find that these two processes are sensitive to different gluon Sivers functions, which can be expressed as linear combinations of two distinct, universal gluon distributions. We therefore define proper observables which could allow for a separate extraction of these two independent Sivers functions. At the same time, we show how it would be possible to discriminate between the GPM and the CGI-GPM approaches by comparing the corresponding estimates of SSAs with present and future experimental results at RHIC.
We report on a recent investigation of the single spin asymmetry (SSA) in low virtuality electroproduction of $J/psi$ in color evaporation model. We show that this can be used as a probe for the still unknown gluon Sivers function.
Within a TMD approach we discuss the impact of quasi-real (Weizsacker-Williams) photon contribution to the transverse single-spin asymmetry, $A_N$, for the inclusive process $ell p^uparrow to pi, X$. This study extends a previous one where only the leading-order contribution was taken into account. Predictions are obtained adopting the Sivers and transversity distributions and the Collins fragmentation functions as extracted from fits to the azimuthal asymmetries measured in semi-inclusive deep inelastic scattering and $e^+e^-$ annihilation processes. The description of the available data is very good, showing a clear general improvement with respect to the previous analysis (already quite promising). This result represents a further step towards a unified TMD treatment of SSAs in $ell,p^uparrow toell, h, X$ and $ell ,p^uparrow to h, X$ processes.
We suggest inclusive hadron production in ultra-peripheral proton-nucleus collisions (UPCs) $p^uparrow A to h AX$ as a new channel to investigate single spin asymmetries (SSAs), in particular, to test the assumed dominance of the contribution from twist-three fragmentation functions. The UPC cross sections are obtained by considering the photoproduction limit of semi-inclusive deep inelastic scattering (SIDIS). In particular, we find simple formulas for the polarized UPC cross sections in the collinear twist-three framework. We then numerically calculate the fragmentation contribution to SSA in $p^uparrow A to pi A X$ at $sqrt{s} = 200$ GeV and find a few percent asymmetry in the forward region.
We present estimates of transverse single-spin asymmetry in prompt photon production in the scattering of low virtuality photons off a polarized proton target and discuss the possibility of using this as a probe to get information about the gluon Sivers function (GSF). Using a generalized parton model (GPM) framework, we estimate the asymmetries at electron-ion collider energy ($sqrt{s}$ =140 GeV) taking into account both direct and resolved photon processes and find that the dominant contribution, up to $10%$, comes from quark Sivers function (QSF) while the contribution from GSF is found to be up to $2%$. However, upon taking into account the effects of the process-dependent initial and final state interactions through the color-gauge invariant generalized parton model approach we find that the situation is significantly changed, with near zero contributions from the QSFs and up to a $1%$ level contribution from the textit{f}-type GSF. Our results indicate that this process may be useful for distinguishing between GPM and color-gauge invariant generalized parton models and can be used as a good probe of textit{f}-type GSF.
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