arXiv subjects

Emanuele R. Nocera

Publications and source records attributed to Emanuele R. Nocera.

At least 19 recordsLinked to original sources

arXiv2026

Global analyses of helicity-dependent parton distribution functions

Helicity-dependent, or polarised, parton distribution functions describe the longitudinal polarisation of quarks, antiquarks, and gluons inside a polarised nucleon. They encode how the spin of a fast-moving proton or neutron is shared among its partonic constituents and are therefore central to the modern understanding of nucleon spin structure in Quantum Chromodynamics. Helicity PDFs are extracted from global QCD analyses of polarised hard-scattering data, including inclusive deep-inelastic scattering, semi-inclusive deep-inelastic scattering, and polarised proton-proton collisions. This article reviews the definition and physical interpretation of polarised PDFs, the perturbative QCD framework used to determine them, the experimental observables that constrain the different parton flavours, and the statistical methodology of global analyses. The state of the art in polarised PDF determination is presented, together with the impact expected from future measurements at the Electron-Ion Collider.

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arXiv2026

Impact of Z-boson transverse-momentum resummation on PDF determination

We study the impact of small-transverse-momentum resummation for neutral-current Drell-Yan lepton-pair production on the determination of collinear parton distribution functions (PDFs). We focus on measurements of the Z-boson transverse-momentum spectrum performed by ATLAS and CMS at the LHC at centre-of-mass energies of 8 and 13 TeV, and include them in PDF fits based on the NNPDF methodology. Theoretical predictions are computed at next-to-next-to-leading order (NNLO) in perturbative QCD and are supplemented with small-transverse-momentum resummation corrections at next-to-next-to-next-to-leading logarithmic accuracy obtained with RadISH. Missing higher-order uncertainties are accounted for through a theory covariance matrix constructed from renormalisation- and factorisation-scale variations. We first revisit the treatment of the 8 TeV data, replacing the fixed-order predictions used in previous analyses with numerically stable NNLO calculations, and removing the additional numerical uncertainties introduced in earlier fits. We then assess the impact of the 13 TeV measurements, of resummation corrections, and of progressively lowering the minimum cut on the dilepton transverse momentum. We find that resummation improves the description of the Z boson transverse-momentum data and is essential for ensuring the overall consistency of the PDF fits. Nevertheless, it does not conclusively support extending the fitted kinematic region to transverse momenta below a few tens of GeV. The impact of resummation on PDFs is moderate, leading primarily to a stabilisation of the gluon PDF in a kinematic region of relevance for LHC phenomenology. Finally, we comment on the fact that the treatment of correlations among theoretical uncertainties may play a central role in PDF fits to measurements with percent- and sub-percent-level precision.

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arXiv2026

PineAPPLv1: fast and flexible theory predictions for present and future colliders

We present PineAPPLv1, a library designed to provide accurate and flexible interpolation tables of partonic cross sections that can be convolved with parton distribution functions (PDFs) and fragmentation functions (FFs) for the fast evaluation of high-energy physical observables. The core feature of the new release is the support of multiple convolutions involving initial- and final-state hadronic particles, with any polarisation, that are associated with PDFs and FFs. The library simultaneously supports polarised and unpolarised distributions that obey space-like or time-like evolution, and is developed for an arbitrary number of them, even if physical processes typically only require a few. Control of scale choices when more than one scale characterises a scattering process is also possible. We describe the technical details of the new representation of interpolation coefficients stored in the grid, and we demonstrate the capabilities of the library in a few phenomenological cases of interest. Specifically, we compute predictions for single-inclusive pion production in unpolarised and polarised proton-proton collisions and in semi-inclusive deep-inelastic scattering. We show how, in each case, PDF, FF, and scale uncertainties compare to each other and highlight the potential of PineAPPL as an essential ingredient for precision physics at current and future colliders.

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arXiv2026

Proton-Proton to Antinucleon Cross Sections for Cosmic Ray Applications

We present predictions of inclusive antiproton and antineutron production cross sections in proton-proton collisions relevant to primary and secondary antiproton production in cosmic ray interactions with interstellar matter. Our predictions are based on collinear factorisation in Quantum Chromodynamics and are accurate to next-to-leading order in the perturbative expansion of the strong coupling. We assess the relevance of cross sections measured at collider experiments, such as NA49 at the CERN SPS and ALICE at the LHC, to the kinetic energy ranges accessed by cosmic ray detectors. We characterise the associated uncertainties due to the input parton distribution and fragmentation functions, and to missing higher orders. We critically examine the ~30% excess of antineutron over antiproton production in proton-proton collisions preliminarily reported by the NA49 experiment by combining our predictions with a data-driven model. Our results do not support the NA49 finding, and point to a mild excess of a few percent. We finally show that the NA49 result could only be reconciled with our framework by invoking sizeable differences between antiproton and antineutron production in the poorly constrained region of small transverse momenta of the produced hadron.

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arXiv2025

A Determination of $α_s(m_Z)$ at ${\bf aN^3LO_{QCD}}\otimes {\bf {NLO}_{QED}}$ Accuracy from a Global PDF Analysis

We present a determination of the strong coupling $α_s(m_Z)$ from a global dataset including both fixed-target and collider data from deep-inelastic scattering and a variety of hadronic processes, with a simultaneous determination of parton distribution functions (PDFs) based on the NNPDF4.0 methodology. This determination is performed at NNLO and approximate N$^3$LO (aN$^3$LO) perturbative QCD accuracy, including QED corrections and a photon PDF up to NLO accuracy. We extract $α_s$ using two independent methodologies, both of which take into account the cross-correlation between $α_s$ and the PDFs. The two methodologies are validated by closure tests that allow us to detect and remove or correct for several sources of bias, and lead to mutually consistent results. We account for all correlated experimental uncertainties, as well as correlated theoretical uncertainties related to missing higher order perturbative corrections (MHOUs). We study the perturbative convergence of our results and the impact of QED corrections. We assess individual sources of uncertainty, specifically MHOUs and the value of the top quark mass. We provide a detailed appraisal of methodological choices, including the choice of input dataset, the form of solution of evolution equation, the treatment of the experimental covariance matrix, and the details of Monte Carlo data generation. We find $α_s(m_Z)=0.1194^{+0.0007}_{-0.0014}$ at aN$^3$LO$_{\rm QCD}\otimes {\rm NLO}_{\rm QED}$ accuracy, consistent with the latest PDG average and with recent lattice results.

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arXiv2025

Parton distributions confront LHC Run II data: a quantitative appraisal

We present a systematic comparison of theoretical predictions and various high-precision experimental measurements, specifically of differential cross sections performed by the LHC run II for Drell-Yan gauge boson, top-quark pair, single-inclusive jet and di-jet production, and by HERA for single-inclusive jet and di-jet production. Theoretical predictions are computed at next-to-next-to-leading order (NNLO) accuracy in perturbative Quantum Chromodynamics. The most widely employed sets of Parton Distribution Functions (PDFs) are used, and PDF, strong coupling, and missing higher order uncertainties are taken into account. We quantitatively assess the predictive power of each PDF set and the contribution of the different sources of experimental and theoretical uncertainty to the agreement between data and predictions. We show that control over all of these aspects is crucial to precision physics studies, such as the determination of Standard Model parameters at the LHC.

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arXiv2025

Combination of aN$^3$LO PDFs and implications for Higgs production cross-sections at the LHC

We discuss how the two existing approximate N$^3$LO (aN$^3$LO) sets of parton distributions (PDFs) from the MSHT20 and NNPDF4.0 series can be combined for LHC phenomenology, both in the pure QCD case and for the QCD$\otimes$QED sets that include the photon PDF. Using the resulting combinations, we present predictions for the total inclusive cross-section for Higgs production in gluon fusion, vector boson fusion, and associated production at the LHC Run-3. For the gluon fusion and vector boson fusion channels, the corrections that arise when using correctly matched aN$^3$LO PDFs with N$^3$LO cross section calculations, compared to using NNLO PDFs, are significant, in many cases larger than the PDF uncertainty, and generally larger than the differences between the two aN$^3$LO PDF sets entering the combination. The combined aN$^3$LO PDF sets, MSHT20xNNPDF40_an3lo and MSHT20xNNPDF40_an3lo_qed, are made publicly available in the LHAPDF format and can be readily used for LHC phenomenology.

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arXiv2025

NNPDFpol2.0: a global determination of polarised PDFs and their uncertainties at next-to-next-to-leading order

We present NNPDFpol2.0, a new set of collinear helicity parton distribution functions (PDFs) of the proton based on legacy measurements of structure functions in inclusive neutral-current longitudinally polarised deep-inelastic scattering (DIS), and of W -boson, single-inclusive, and di-jet production asymmetries in longitudinally polarised proton-proton collisions. The determination is accurate to next-to-next-to-leading order in the strong coupling, and includes heavy quark mass corrections in the analysis of DIS data. Uncertainties due to missing higher-order corrections are systematically incorporated by means of a covariance matrix determined by scale variations. NNPDFpol2.0 is based on a machine learning methodology, that makes use of Monte Carlo sampling for the representation of uncertainties into PDFs, of a neural network for the parametrisation of PDFs, of stochastic gradient descent for the optimisation of PDF parameters, and of hyperoptimisation for the selection of the best fitting model. We study the impact on PDFs of higher-order corrections, of the positivity constraint, and of the data. We demonstrate two phenomenological applications of NNPDFpol2.0, specifically the determination of the proton spin fraction carried by gluons and quarks, and of theoretical predictions for single-hadron production in longitudinally polarised DIS and proton-proton collisions.

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arXiv2025

Helicity-dependent parton distribution functions at next-to-next-to-leading order accuracy from inclusive and semi-inclusive deep-inelastic scattering data

We present MAPPDFpol1.0, a new determination of the helicity-dependent parton distribution functions (PDFs) of the proton from a set of longitudinally polarised inclusive and semi-inclusive deep-inelastic scattering data. The determination includes, for the first time, next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural-network parametrisation of PDFs with a Monte Carlo representation of their uncertainties. We discuss the quality of the determination, in particular its dependence on higher-order corrections, on the choice of data set, and on theoretical constraints.

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arXiv2024

The Path to N$^3$LO Parton Distributions

We extend the existing leading (LO), next-to-leading (NLO), and next-to-next-to-leading order (NNLO) NNPDF4.0 sets of parton distribution functions (PDFs) to approximate next-to-next-to-next-to-leading order (aN$^3$LO). We construct an approximation to the N$^3$LO splitting functions that includes all available partial information from both fixed-order computations and from small and large $x$ resummation, and estimate the uncertainty on this approximation by varying the set of basis functions used to construct the approximation. We include known N$^3$LO corrections to deep-inelastic scattering structure functions and extend the FONLL general-mass scheme to $\mathcal{O}\left( α_s^3\right)$ accuracy. We determine a set of aN$^3$LO PDFs by accounting both for the uncertainty on splitting functions due to the incomplete knowledge of N$^3$LO terms, and to the uncertainty related to missing higher corrections (MHOU), estimated by scale variation, through a theory covariance matrix formalism. We assess the perturbative stability of the resulting PDFs, we study the impact of MHOUs on them, and we compare our results to the aN$^3$LO PDFs from the MSHT group. We examine the phenomenological impact of aN$^3$LO corrections on parton luminosities at the LHC, and give a first assessment of the impact of aN$^3$LO PDFs on the Higgs and Drell-Yan total production cross-sections. We find that the aN$^3$LO NNPDF4.0 PDFs are consistent within uncertainties with their NNLO counterparts, that they improve the description of the global dataset and the perturbative convergence of Higgs and Drell-Yan cross-sections, and that MHOUs on PDFs decrease substantially with the increase of perturbative order.

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arXiv2024

Photons in the proton: implications for the LHC

We construct a set of parton distribution functions (PDFs), based on the recent NNPDF4.0 PDF set, that also include a photon PDF. The photon PDF is constructed using the LuxQED formalism, while QED evolution accounting for O(alpha), O(alpha alphas) and O(alpha^2) corrections is implemented and benchmarked by means of the EKO code. We investigate the impact of QED effects on NNPDF4.0, and compare our results both to our previous NNPDF3.1QED PDF set and to other recent PDF sets that include the photon. We assess the impact of photon-initiated processes and electroweak corrections on a variety of representative LHC processes, and find that they can reach the 5% level in vector boson pair production at large invariant mass.

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arXiv2024

Determination of the theory uncertainties from missing higher orders on NNLO parton distributions with percent accuracy

We include uncertainties due to missing higher order corrections to QCD computations (MHOU) used in the determination of parton distributions (PDFs) in the recent NNPDF4.0 set of PDFs. We use our previously published methodology, based on the treatment of MHOUs and their full correlations through a theory covariance matrix determined by scale variation, now fully incorporated in the new NNPDF theory pipeline. We assess the impact of the inclusion of MHOUs on the NNPDF4.0 central values and uncertainties, and specifically show that they lead to improved consistency of the PDF determination with an ensuing moderate reduction of PDF uncertainties at NNLO.

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arXiv2024

The intrinsic charm quark valence distribution of the proton

We provide a first quantitative indication that the wave function of the proton contains unequal distributions of charm quarks and antiquarks, i.e. a nonvanishing intrinsic valence charm distribution. A significant nonvanishing valence component cannot be perturbatively generated, hence our results reinforce previous evidence that the proton contains an intrinsic (i.e., not radiatively generated) charm quark component. We establish our result through a determination of the parton distribution functions (PDFs) of charm quarks and antiquarks in the proton. We propose two novel experimental probes of this intrinsic charm valence component: D-meson asymmetries in Z+c-jet production at the LHCb experiment, and flavor-tagged structure functions at the Electron-Ion Collider.

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arXiv2024

Heavy Quarks in Polarised Deep-Inelastic Scattering at the Electron-Ion Collider

We extend the FONLL general-mass variable-flavour-number scheme to the case of longitudinally polarised DIS structure functions, accounting for perturbative corrections up to $\mathcal{O}(α_s^2)$. We quantify the impact of charm quark mass and higher-order perturbative corrections on projected measurements of inclusive and charm-tagged longitudinal asymmetries at the Electron-Ion Collider (EIC) and at the Electron-ion collider in China (EicC). We demonstrate how the inclusion of these corrections is essential to compute predictions with an accuracy that matches the projected precision of the measurements. The computation is made publicly available through the open-source EKO and YADISM programs

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arXiv2022

Parton Distributions and New Physics Searches: the Drell-Yan Forward-Backward Asymmetry as a Case Study

We discuss the sensitivity of theoretical predictions of observables used in searches for new physics to parton distributions (PDFs) at large momentum fraction $x$. Specifically, we consider the neutral-current Drell-Yan production of gauge bosons with invariant masses in the TeV range, for which the forward-backward asymmetry of charged leptons from the decay of the gauge boson in its rest frame is a traditional probe of new physics. We show that the qualitative behaviour of the asymmetry depends strongly on the assumptions made in determining the underlying PDFs. We discuss and compare the large-$x$ behaviour of various different PDF sets, and find that they differ significantly. Consequently, the shape of the asymmetry observed at lower dilepton invariant masses, where all PDF sets are in reasonable agreement because of the presence of experimental constraints, is not necessarily reproduced at large masses where the PDFs are mostly unconstrained by data. It follows that the shape of the asymmetry at high masses may depend on assumptions made in the PDF parametrization, and thus deviations from the traditionally expected behaviour cannot be taken as a reliable indication of new physics. We demonstrate that forward-backward asymmetry measurements could help in constraining PDFs at large $x$ and discuss the accuracy that would be required to disentangle the effects of new physics from uncertainties in the PDFs in this region.

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arXiv2022

Response to "Parton distributions need representative sampling"

We respond to the criticism raised by Courtoy et al., in which the faithfulness of the NNPDF4.0 sampling is questioned and an under-estimate of the NNPDF4.0 PDF uncertainties is implied. We list, correct, and clarify in detail a number of inaccurate or misleading claims that are made in this Reference. Specifically, we explain and explicitly demonstrate why the central value of the PDF distribution does not generally coincide with the absolute minimum of the $χ^{2}$ to the data. We examine some PDFs that have been constructed in the above study and claimed to be "good solutions": we show that similar PDFs are found with the NNPDF methodology, but with very low probability.

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arXiv2022

Regularising experimental correlations in LHC data: theory and application to a global analysis of parton distributions

We show how an inaccurate determination of experimental uncertainty correlations in high-precision LHC measurements may undermine the reliability of the associated $χ^2$. We formulate the problem rigorously, and devise a regularisation procedure that increases the stability of the $χ^2$ by altering the covariance matrix of the measurement as little as possible. We apply the procedure to the NNPDF4.0 global analysis of parton distribution functions that utilises a large amount of LHC measurements. We find that the regularised $χ^2$ of the NNPDF4.0 determination is lowered by about $3σ$, without significantly altering the resulting PDFs upon refitting.

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arXiv2022

Pion and kaon fragmentation functions at next-to-next-to-leading order

We present a new determination of unpolarised charged pion and kaon fragmentation functions from a set of single-inclusive electron-positron annihilation and lepton-nucleon semi-inclusive deep-inelastic scattering data. The determination includes next-to-next-to-leading order QCD corrections to both processes, and is carried out in a framework that combines a neural-network parametrisation of fragmentation functions with a Monte Carlo representation of their uncertainties. We discuss the quality of the determination, in particular its dependence on higher order corrections.

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