arXiv subjects

M. Anselmino

Publications and source records attributed to M. Anselmino.

At least 55 records · Page 3Linked to original sources

arXiv2009

Sivers and Collins Effects: from SIDIS to Proton-Proton Inclusive Pion Production

We consider the Sivers, Collins and transversity functions as extracted from SIDIS and e+e- experimental data and investigate to what extent they might explain the large Single Spin Asymmetries (SSA) observed in proton-proton inclusive processes. This phenomenological study is performed within the TMD factorization scheme. As the SIDIS data cover only a limited range of x values (x < 0.3), we allow for different large $x$ behaviours of the SIDIS Sivers functions and transversity distributions. We conclude that, within the available experimental constraints, one cannot observe any clear universality breaking effect for the Sivers functions.

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arXiv2009

Single spin asymmetries in l p --> h + X processes

We study the transverse single spin asymmetry (SSA), A_N, for the single inclusive process l p (transv. polarized) --> h + X, in a perturbative QCD factorization scheme with inclusion of spin and transverse momentum dependent (TMD) distributions. By adopting the relevant TMDs (Sivers and Collins functions) as extracted from semi-inclusive deep inelastic scattering (SIDIS) and e+e- data, predictions for these SSAs are given. A measurement of A_N for this process could then provide a direct test of the validity of the TMD factorization.

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arXiv2009

Sivers effect in Drell-Yan processes

The Sivers distributions recently extracted from semi-inclusive deep inelastic scattering data [1] are used to compute estimates for Sivers asymmetries in Drell-Yan processes which are being planned at several facilities (RHIC, COMPASS, J-PARC, PAX, PANDA, NICA (JINR) and SPASCHARM (IHEP)). Most of these asymmetries turn out to be large and could allow a clear test of the predicted sign change of the Sivers distributions when active in SIDIS and Drell-Yan processes. This is regarded as a fundamental test of our understanding, within QCD and the factorization scheme, of single spin asymmetries.

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arXiv2009

Sivers Effect for Pion and Kaon Production in Semi-Inclusive Deep Inelastic Scattering

We study the Sivers effect in the transverse single spin asymmetries (SSA) for pion and kaon production in semi-inclusive deep inelastic scattering (SIDIS) processes. We perform a fit of A^sin(phi_h-phi_S)_UT which, by including recent high statistics experimental data for pion and kaon production from HERMES and COMPASS Collaborations, allows a new determination of the Sivers distribution functions for quarks and antiquarks with u, d and s flavours. Estimates for forthcoming SIDIS experiments at COMPASS and JLab are given.

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arXiv2008

Update on transversity and Collins functions from SIDIS and e+ e- data

We present an update of a previous global analysis of the experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e+ e- -> h1 h2 X processes, from the Belle Collaboration. Compared to the first extraction, a more precise determination of the Collins fragmentation function and the transversity distribution function for u and d quarks is obtained.

hep-ph↗

arXiv2008

Intrinsic parton motion soft mechanisms and the longitudinal spin asymmetry A_LL in high energy pp -> pi X

The longitudinal double spin asymmetry A_LL in the reaction pp --> pi X has been measured at RHIC with extremely interesting consequences. If the gluon polarization in a proton were as big as needed to resolve the famous "spin crisis" then A_LL would be large and positive. Latest RHIC results indicate that A_LL is small and disfavour large positive values of the gluon polarization. We examine whether the soft mechanisms (Collins, Sivers, Boer-Mulders), essential for generating transverse single spin asymmetries, have any significant influence on A_LL, and whether they could alter the conclusion that the gluon polarization is necessarily small. It turns out that the contribution from these effects is essentially negligible.

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arXiv2008

Sivers and Collins effects in polarized pp scattering processes

We summarize the present phenomenology of Sivers and Collins effects for transverse single spin asymmetries in polarized proton-proton collisions within the framework of the generalized parton model (GPM). We will discuss a reassessment of the Collins effect and some preliminary predictions for SSA's in p(pol) p -> pi,K + X processes at RHIC obtained using updated information from SIDIS data and a new set of meson fragmentation functions.

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arXiv2008

The Sivers Function from SIDIS Data

We study the Sivers effect in transverse single spin asymmetries (SSA) for pion and kaon production in Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes. We perform a fit of A^{sin(phi_h-phi_S)}_UT taking into account the recent data from HERMES and COMPASS Collaborations, which allow a new determination of the Sivers distribution functions for quark and anti-quark with u, d and also s flavours. Estimates for forthcoming SIDIS experiments at COMPASS and JLab are given.

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arXiv2008

Transversity and Collins Fragmentation Functions: Towards a New Global Analysis

A new, preliminary global analysis of the experimental data on azimuthal asymmetries in SIDIS from HERMES and COMPASS collaborations, and in e+e- --> h_1 h_2 X processes from the BELLE collaboration, is performed. The new data allow for a more precise determination of the Collins fragmentation function and of the transversity distribution function for $u$ and $d$ quarks, in comparison with the results of our previous analysis. Estimates for the single spin asymmetry A_UT^{\sin(ϕ_h + ϕ_S)} at JLab and COMPASS, operating on a transversely polarized proton target, are presented.

hep-ph↗

arXiv2007

Transversity and Collins Functions: from e+ e- --> h1 h2 X to SIDIS Processes

We present [1] the first simultaneous extraction of the transversity distribution and the Collins fragmentation function, obtained through a combined analysis of experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e+ e- --> h1 h2 X processes, from the Belle Collaboration.

hep-ph↗

arXiv2007

Transversity and Collins functions from SIDIS and e+e- data

A global analysis of the experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e+e- --> h1 h2 X processes, from the BELLE Collaboration, is performed. It results in the extraction of the Collins fragmentation function and, for the first time, of the transversity distribution function for u and d quarks. These turn out to have opposite signs and to be sizably smaller than their positivity bounds. Predictions for the azimuthal asymmetry A_{UT}^{sin(phi_h + phi_S)}, as will soon be measured at JLab and COMPASS operating on a transversely polarized proton target, are then presented.

hep-ph↗

arXiv2007

Transversity and Transverse Spin in Nucleon Structure through SIDIS at Jefferson Lab

The JLab 12 GeV upgrade with a proposed solenoid detector and the CLAS12 detector can provide the granularity and three-dimensional kinematic coverage in longitudinal and transverse momentum, $0.1\le x \le 0.5$, $0.3 \le z \le 0.7$ with $P_T \le 1.5 {\rm GeV}$ to precisely measure the leading twist chiral-odd and $T$-odd quark distribution and fragmentation functions in SIDIS. The large $x$ experimental reach of these detectors with a 12 GeV CEBAF at JLab makes it {\em ideal} to obtain precise data on the {\em valence-dominated} transversity distribution function and to access the tensor charge.

hep-ph↗

arXiv2006

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.

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arXiv2006

Constraints on the gluon Sivers distribution via transverse single spin asymmetries at midrapidity in p(transv. polarized) p -> pi^0 X processes at BNL RHIC

We consider the recent RHIC data on the transverse single spin asymmetry (SSA) A_N, measured in p(transv. polarized) p -> pi^0 X processes at mid-rapidity by the PHENIX collaboration. The measurement is consistent with a vanishing SSA. 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. It turns out that, in the kinematical region of the data, only the gluon Sivers effect could give a large contribution to A_N; its vanishing value is thus an indication about the possible size of the gluon Sivers function (GSF). Approximate upper limits on its magnitude are derived. Additional constraints obtained combining available parameterizations of the quark Sivers function and the Burkardt sum rule (BSR) for the Sivers distributions are also discussed.

hep-ph↗

arXiv2006

Transverse momentum dependence of the quark helicity distributions and the Cahn effect in double-spin asymmetry $A_{LL}$ in Semi Inclusive DIS

Within the LO QCD parton model of Semi Inclusive Deep Inelastic Scattering, $\ell N \to \ell h X$, with unintegrated quark distribution and fragmentation functions, we study the $\bfP_{hT}$ dependence of the double longitudinal-spin asymmetry $A_{LL}$. We include 1/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 $A_{LL}$ and of the weighted DSA $A_{LL}^{\cosϕ_h}$ allows to extract the transverse momentum dependence of the unintegrated helicity distribution function $g_{1L}^q(x,k_\perp)$ [or $Δq(x, k_\perp)]$. Predictions, based on some models for the unknown functions, are given for ongoing COMPASS, HERMES and JLab experiments.

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arXiv2006

Semi-Inclusive Deep Inelastic Scattering processes from small to large P_T

We consider the azimuthal and $P_T$ dependence of hadrons produced in unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, within the factorized QCD parton model. It is shown that at small $P_T$ values, $P_T \lsim 1$ GeV/c, lowest order contributions, coupled to unintegrated (Transverse Momentum Dependent) quark distribution and fragmentation functions, describe all data. At larger $P_T$ values, $P_T \gsim 1$ GeV/c, the usual pQCD higher order collinear contributions dominate. Having explained the full $P_T$ range of available data, we give new detailed predictions concerning the azimuthal and $P_T$ dependence of hadrons which could be measured in ongoing or planned experiments by HERMES, COMPASS and JLab collaborations.

hep-ph↗

arXiv2006

General partonic structure for hadronic spin asymmetries

The high energy and large p_T inclusive polarized process, (A, S_A) + (B, S_B) --> C + X, is considered under the assumption of a generalized QCD factorization scheme. For the first time all transverse motions, of partons in hadrons and of hadrons in fragmenting partons, are explicitly taken into account; the elementary interactions are computed at leading order with noncollinear exact kinematics, which introduces many phases in the expressions of their helicity amplitudes. Several new spin and k_T dependent soft functions appear and contribute to the cross sections and to spin asymmetries; we put emphasis on their partonic interpretation, in terms of quark and gluon polarizations inside polarized hadrons. Connections with other notations and further information are given in some Appendices. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A_N, for p(transv. polarized) p --> pion + X processes is considered in more detail, and all contributions are evaluated numerically by saturating unknown functions with their upper positivity bounds. It is shown that the integration of the phases arising from the noncollinear kinematics strongly suppresses most contributions to the single spin asymmetry, leaving at work predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.

hep-ph↗

arXiv2006

General helicity formalism for Single and Double Spin Asymmetries in p p --> pion + X

We consider within a generalized QCD factorization approach, the high energy inclusive polarized process p p --> pion + X, including all intrinsic partonic motions. Several new spin and k_T-dependent soft functions appear and contribute to cross sections and spin asymmetries. We present here formal expressions for transverse single spin asymmetries and double longitudinal ones. The transverse single spin asymmetry, A_N, is considered in detail, and all contributions are evaluated numerically. It is shown that the azimuthal phase integrations strongly suppress most contributions, leaving at work mainly the Sivers effect.

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