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S. Liuti

Publications and source records attributed to S. Liuti.

50 records · Page 3Linked to original sources
arXiv2004

Generalized Parton Distributions and Color Transparency

We study the structure of generalized parton distributions in impact parameter space with the aim of determining the size and role of small transverse separations components in the quarks wave function. We analyze the relation between transverse momentum components and transverse separations. Wave functions with large transverse momentum components can simultaneously reproduce the behavior of the Dirac form factor at large momentum transfer, and of the deep inelastic structure functions at Bjorken x -> 1. The presence of large momentum components does not ensure, however, the dominance of small transverse distances at large x. We suggest that experiments measuring the attenuation of hadrons in the nuclear medium, or the onset of color transparency, can provide an alternative source of information on generalized parton distributions, by mapping out the behavior of the transverse components of the wave function.

hep-ph↗
arXiv2003

Parton-Hadron Duality in Unpolarised and Polarised Structure Functions

We study the phenomenon of parton-hadron duality in both polarised and unpolarised electron proton scattering using the HERMES and the Jefferson Lab data, respectively. In both cases we extend a systematic perturbative QCD based analysis to the integrals of the structure functions in the resonance region. After subtracting target mass corrections and large x resummation effects, we extract the remaining power corrections up to order 1/Q^2. We find a sizeable suppression of these terms with respect to analyses using deep inelastic scattering data. The suppression appears consistently in both polarised and unpolarised data, except for the low Q^2 polarised data, where a large negative higher twist contribution remains. Possible scenarios generating this behavior are discussed.

hep-ph↗
arXiv2003

Deep inelastic scattering from A=3 nuclei and the neutron structure function

We present a comprehensive analysis of deep inelastic scattering from He-3 and H-3, focusing in particular on the extraction of the free neutron structure function, F_2^n. Nuclear corrections are shown to cancel to within 1-2% for the isospin-weighted ratio of He-3 to H-3 structure functions, which leads to more than an order of magnitude improvement in the current uncertainty on the neutron to proton ratio F_2^n/F_2^p at large x. Theoretical uncertainties originating from the nuclear wave function, including possible non-nucleonic components, are evaluated. Measurement of the He-3 and H-3 structure functions will, in addition, determine the magnitude of the EMC effect in all A < 4 nuclei.

nucl-th↗
arXiv2003

Isospin Dependence of Power Corrections in Deep Inelastic Scattering

We present results of a perturbative QCD analysis of deep inelastic measurements of both the deuteron and proton structure functions. We evaluate the theoretical uncertainty associated to nuclear effects in the deuteron, and we extract simultaneously the isospin depedendence of: i)the higher twists terms; ii) the ratio of the longitudinal to transverse cross sections; iii) the ratio of the neutron to proton structure functions. The extraction of the latter, in particular, has been at the center of an intense debate. Its accurate determination is crucial both theoretically and for the interpretation of the more precise neutrino experiments including the newly planned high intensity 50 GeV proton synchrotron.

hep-ph↗
arXiv2002

Unraveling Violations of Parton-Hadron Duality in ep Scattering

Recent studies of the Q^2 dependence of ep scattering in the large x region and in the Q^2 range: 1 < Q^2 2.4 GeV^2 At lower values of W^2, duality is found to be significantly violated by an amount that cannot be parametrized in terms of the first few terms of a series of power corrections. We present a dynamical model that explains the Q^2 dependence of the data: at low W^2, non-partonic components given by color neutral clusters dominate the cross section and the Q^2 dependence is governed by their mass spectrum, predicted within the preconfiment property of Q CD; at large W^2 the structure function is determined by a convolution of the cluster mass spectrum with the parton distributions.

hep-ph↗
arXiv2001

Perturbative QCD Analysis of Local Duality in a fixed W^2 Framework

We study the global Q^2 dependence of large x, F_2 nucleon structure function data, with the aim of providing a perturbative-QCD based, quantitative analysis of parton-hadron duality. As opposed to previous analyses at fixed x, we use a framework in fixed W^2. We uncover a breakdown of the twist-4 approximation with a renormalon type improvement at O(1/Q^4) which, by affecting the initial evolution of parton distributions, will have consequences for pQCD analyses also at large x and very large Q^2.

hep-ph↗
arXiv2001

Moments of the Proton F2 Structure Function at Low Q2

The Q^2 dependence of inclusive electron-proton scattering F_2 structure function data in both the nucleon resonance region and the deep inelastic region, at momentum transfers below 5 (GeV/c)^2, is investigated. Moments of F_2 are constructed, down to momentum transfers of Q^2 ~ 0.1 (GeV/c)^2. The second moment is only slowly varying with Q^2 down to Q^2 ~ 1 (GeV/c)^2, which is a reflection of duality. Below Q^2 of 1 (GeV/c)^2, the Q^2 dependence of the moments is predominantly governed by the elastic contribution, whereas the inelastic channels still seem governed by local duality.

hep-ph↗
arXiv2000

An Analysis of the Asymptotic Limit of Gluon Shadowing

We examine the gluon distributions in nuclei in the asymptotic region defined by $Q^2 \to \infty$, $x \to 0$. An analysis using the Double Asymptotic Scaling variables of Ball and Forte is proposed. New scaling relations are predicted which can help disentangling the different mechanisms of low $x$ perturbative QCD evolution in nuclei.

hep-ph↗
arXiv1998

A Systematic Study of Power Corrections from World Deep Inelastic Scattering Measurements

By performing an analysis in moment space using high statistics DIS world data, we extract the values of both the QCD parameter $Λ^{(4)}_{\bar{MS}}$ up to NLO and of the power corrections to the proton structure function, $F_2$. At variance with previous analyses, the use of moments allows us to extend the kinematical range to larger values of $x$, where we find that power corrections are quantitatively more important. Our results are consistent with the $n$ dependence predicted by IR renormalon calculations. We discuss preliminary results on nuclear targets with the intent of illustrating a possible strategy to disentangle power corrections ascribed to IR renormalons from the ones generated dynamically e.g. from rescattering in the final state. The latter appear to be modified in nuclear targets.

hep-ph↗
arXiv1997

Off-shell Corrections and Moments of the Deep Inelastic Nuclear Structure Functions

We present an improved method for handling off-shell effects in deep inelastic nuclear scattering. With a firm understanding of the effects of the nuclear wave function, including these off-shell corrections as well as binding and nucleon-nucleon correlations, we can begin to examine the role of QCD in nuclei through an analysis of the moments of the nuclear structure function. Our analysis is aimed at extracting the Q^2 dependence of the moments of the nucleon structure function by using the recent high x world Iron data and by properly removing nuclear effects from the perturbative contribution. In addition, we compare quantitatively the behavior of the extracted moments with a simple O(1/Q^2) phenomenological form and we determine the mass term for this parametrization.

hep-ph↗
arXiv1995

Accidental $ξ$-scaling as a Signature of Nuclear Effects at $x>1$

We propose an interpretation of the $ξ$-scaling behavior of nuclear structure functions observed at Bjorken $x>1$ and $Q^2 \lesssim 4 \, {\rm (GeV/c)^2}$. We show that at $ξ\gtrsim 1$, $ξ$-scaling might arise accidentally because of the approximate cancellation of two different $Q^2$-dependent effects, namely Final State Interactions and the effects implicit in the choice of the scaling variable $ξ$. We provide a new convolution formula for the nuclear structure function in terms of $ξ$ and make predictions for the kinematical regions where Final State Interactions are expected to be small and the suggested balancing of scaling violations is expected to break down. Our analysis is aimed at the final goal of clarifying the range of applicability of local duality ideas in nuclei.

hep-ph↗
arXiv1995

Can a Highly Virtual Nucleon Experience Final State Interactions in Electron-Nucleus Scattering?

We discuss how the virtuality of the struck particle may affect the final state interactions in electron-nucleus scattering. The extent to which short range correlations inhibit rescattering taking place within the range of the repulsive core of the NN interaction is quantitatively analyzed. The possible modifications of the nucleon-nucleon scattering amplitude associated with the virtuality is also studied, within the framework of a nonrelativistic model. The results suggest that the on shell approximation can be safely employed in the kinematical region relevant to the analysis of the available inclusive data at large momentum transfer and low energy loss.

hep-ph↗
arXiv1994

Consequences of Nuclear Shadowing for Heavy Quarkonium Production in Hadron-Nucleus Interactions

We study nuclear shadowing in $J/ψ$ and $Υ$ production in hadron-nucleus interactions and in nucleus-nucleus collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider. %We define the regions in $x_f$ where nuclear shadowing begins %to set in for \jp\ and \up. As a consequence of the perturbative $Q^2$-dependence of gluon shadowing, we predict that $Υ$ production is less suppressed than the $J/ψ$. We show that antishadowing leads to enhanced \jp\ production at $x_f \lesssim 0$, an effect reduced for $Υ$ production.

hep-ph↗