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F. Murgia

Publications and source records attributed to F. Murgia.

At least 37 records · Page 2Linked to original sources
arXiv2013

Simultaneous extraction of transversity and Collins functions from new SIDIS and e+e- data

We present a global re-analysis of the most recent experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering, from the HERMES and COMPASS Collaborations, and in e+e- --> h_1 h_2 X processes, from the Belle Collaboration. The transversity and the Collins functions are extracted simultaneously, in the framework of a revised analysis in which a new parameterisation of the Collins functions is also tested.

hep-ph↗
arXiv2013

On the potential role of the Collins effect in A_N in pp --> pion X

Transverse single spin asymmetries in pp --> pion X processes, while on a quite firm ground experimentally, are still a much debated phenomenological issue. We consider them in a transverse momentum dependent factorization scheme. After revisiting a previous result, we give new estimates of the Collins contribution by adopting the latest information on the Collins and transversity functions, as extracted from SIDIS and e+e- data.

hep-ph↗
arXiv2012

On the role of Collins effect in the single spin asymmetry A_N in p(transv. polarized) p --> h X processes

The much debated issue of the transverse single spin asymmetry A_N observed in the inclusive large P_T production of a single hadron in pp interactions, p(transv. polarized) p --> pion X, is considered in a TMD factorization scheme. A previous result [1,2] stating that the maximum contribution of the Collins effect is strongly suppressed, is revisited, correcting a numerical error. New estimates are given, adopting the Collins functions recently extracted from SIDIS and e+e- data, and phenomenological consequences are discussed.

hep-ph↗
arXiv2011

General Helicity Formalism for Polarized Semi-Inclusive Deep Inelastic Scattering

We study polarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, within the QCD parton model and a factorization scheme, taking into account all transverse motions, of partons inside the initial proton and of hadrons inside the fragmenting partons. We use the helicity formalism. The elementary interactions are computed at LO with non collinear exact kinematics, which introduces phases in the expressions of their helicity amplitudes. Several Transverse Momentum Dependent (TMD) distribution and fragmentation functions appear and contribute to the cross sections and to spin asymmetries. Our results agree with those obtained with different formalisms, showing the consistency of our approach. The full expression for single and double spin asymmetries is derived. Simplified, explicit analytical expressions, convenient for phenomenological studies, are obtained assuming a factorized Gaussian dependence on intrinsic momenta for the TMDs.

hep-ph↗
arXiv2010

New insight on the Sivers transverse momentum dependent distribution function

Polarised Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes allow to study Transverse Momentum Dependent partonic distributions (TMDs), which reveal a non trivial three dimensional internal structure of the hadrons in momentum space. One of the most representative of the TMDs is the so-called Sivers function that describes the distribution of unpolarized quarks inside a transversely polarized proton. We present a novel extraction of the Sivers distribution functions from the most recent experimental data of HERMES and COMPASS experiments. Using suitable parametrizations, within the TMD factorization scheme, and a simple fitting strategy, we also perform a preliminary exploration of the role of the proton sea quarks.

hep-ph↗
arXiv2010

Single spin asymmetries in l p --> h X processes: a test of factorization

Predictions for the transverse single spin asymmetry (SSA), A_N, are given for the inclusive processes l p(transv. pol.) --> h X and l p(transv. pol.) --> jet + X, which could be measured in operating or future experiments. These estimates are based on the Sivers distributions and the Collins fragmentation functions which fit the azimuthal asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) processes (l p(transv. pol.) --> l' h X). The factorization in terms of transverse momentum dependent distribution and fragmentation functions (TMD factorization) - which supplies the theoretical framework in which SIDIS azimuthal asymmetries are analyzed - is assumed to hold also for the l p --> h X inclusive process at large P_T. A measurement of A_N would then provide a direct test of the validity of the TMD factorization in this case and would have important consequences for the study and understanding of SSAs in p p(transv. pol.) --> h X processes.

hep-ph↗
arXiv2009

On the importance of Lorentz structure in the parton model: target mass corrections, transverse momentum dependence, positivity bounds

We show that respecting the underlying Lorentz structure in the parton model has very strong consequences. Failure to insist on the correct Lorentz covariance is responsible for the existence of contradictory results in the literature for the polarized structure function g_2(x), whereas with the correct imposition we are able to derive the Wandzura-Wilczek relation for g_2(x) and the target-mass corrections for polarized deep inelastic scattering without recourse to the operator product expansion. We comment briefly on the problem of threshold behaviour in the presence of target-mass corrections. Careful attention to the Lorentz structure has also profound implications for the structure of the transverse momentum dependent parton densities often used in parton model treatments of hadron production, allowing the k_T dependence to be derived explicitly. It also leads to stronger positivity and Soffer-type bounds than usually utilized for the collinear densities.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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

Azimuthal and Single Spin Asymmetries in Hard Scattering Processes

In this article we review the present understanding of azimuthal and single spin asymmetries for inclusive and semi-inclusive particle production in unpolarized and polarized hadronic collisions at high energy and moderately large transverse momentum. After summarizing the experimental information available, we discuss and compare the main theoretical approaches formulated in the framework of perturbative QCD. We then present in some detail a generalization of the parton model with inclusion of spin and intrinsic transverse momentum effects. In this context, we extensively discuss the phenomenology of azimuthal and single spin asymmetries for several processes in different kinematical configurations. A comparison with the predictions of other approaches, when available, is also given. We finally emphasize some relevant open points and challenges for future theoretical and experimental investigation.

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