Two-photon exchange (TPE) is one of the leading explanations for discrepancies in measurements of the proton electromagnetic form factors. It has been proposed that TPE could impact not only elastic scattering but also the cross sections for both inclusive deep inelastic scattering (DIS) and semi-inclusive DIS, thereby affecting the interpretation of DIS structure functions in terms of parton distributions. It is expected that higher-order QED effects such as TPE should manifest as a deviation from unity in the ratio of e + p and e − p DIS cross sections. We use the existing inclusive e ± p DIS data from HERA and SLAC to constrain higher-order QED effects on inclusive DIS.

A bstract Recent studies have demonstrated that the far-forward physics program of the Large Hadron Collider (LHC) can be useful to probe the hadron structure with GeV-TeV neutrinos and muons. In particular, these studies indicate that the measurement of the muon-ion and neutrino-ion cross-sections by the same experiment is feasible. In this paper, we investigate the impact of nuclear effects on the muon-tungsten ( μW ) and neutrino-tungsten ( νW ) deep inelastic scattering (DIS) events at FASER ν and its proposed upgrade FASER ν 2. We estimate the rates associated with the inclusive cross-sections and for events with a charm tagged in the final state considering different parameterizations for the nuclear parton distribution functions. These results point out that muon and neutrino-induced interactions probe complementary kinematical ranges and that a simultaneous analysis of associated events will allow to test the universality (or not) of the nuclear effects. Moreover, we propose the study of the ratio between the charm tagged and inclusive events in order to discriminate between the distinct modeling of the nuclear effects at small- x . Our results indicate that a future experimental reconstruction of μW and νW DIS events at the LHC is a promising way to improve our understanding of nuclear effects and decrease the current uncertainties in parton distribution functions.

We perform a comprehensive global QCD analysis of spin-dependent parton distribution functions (PDFs), combining all available data on inclusive and semi-inclusive deep-inelastic scattering (DIS), as well as inclusive weak boson and jet production in polarized p p collisions, simultaneously extracting spin-averaged PDFs and fragmentation functions. Including recent Jefferson Lab DIS data at high x , together with subleading power corrections to the leading-twist framework, allows us to verify the stability of the PDFs for W 2 ≥ 4 GeV 2 and quantify the uncertainties on the spin structure functions more reliably. We explore the use of new lattice QCD data on gluonic pseudo-Ioffe time distributions, which, together with jet production and high- x DIS data, improve the constraints on the polarized gluon PDF. The expanded kinematic reach afforded by the data into the high- x region allows us to refine the bounds on higher-twist contributions to the spin structure functions, and test the validity of the Bjorken sum rule.

Abstract The LHC far-forward experiments FASER and SND@LHC have pioneered the detection of TeV-energy neutrinos produced in hard-scattering proton-proton collisions at the LHC. In addition to neutrinos, an intense flux of TeV-energy muons reaches these detectors, representing a dominant background for both neutrino studies and beyond the Standard Model searches. Here we demonstrate that this forward muon flux enables a comprehensive neutral-current deep-inelastic scattering (DIS) program at FASER with a strong kinematical overlap with the Electron Ion Collider. For the Run 3 luminosity of $${\mathcal {L}}_{{\textrm{pp}}}=250$$ L pp = 250 fb $$^{-1},$$ - 1 , more than $$10^5$$ 10 5 inclusive muon DIS events, of which up to $$10^4$$ 10 4 from charm production, are expected at FASER $$\nu .$$ ν . As a representative application, we demonstrate the sensitivity of muon DIS at FASER $$\nu $$ ν to probe the (intrinsic) charm content of the proton at large-x. We also provide predictions for event yields of muon DIS for future FASER runs and for the proposed Forward Physics Facility.

Abstract We extend the recently presented, fully exclusive, next-to-leading-order accurate event generator for the simulation of massless neutral- and charged-current deep inelastic scattering (DIS) to the case of incoming neutrinos. The generator can be used to study neutrino-nucleon interactions at (ultra) high energies, and is relevant for a range of fixed-target collider experiments and large-volume neutrino detectors, investigating atmospheric and astrophysical neutrinos. The matching with multi-purpose event generators such as is performed with the method, and accounts for parton showering and non-perturbative effects such as hadronization. This makes it possible to investigate higher-order perturbative corrections to realistic observables, such as the distribution of charged particles. To illustrate the capabilities of the code we provide predictions for several differential distributions in fixed-target collisions for neutrino energies up to $$1~\textrm{PeV} $$ 1 PeV .

Abstract 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.

We investigate Λ production in semi-inclusive deep-inelastic scattering using a polarized lepton beam and find that the spin transfer is significantly suppressed by target fragmentation. As further demonstrated by a model estimation, experimental data can be well described once the target fragmentation is taken into account, which alleviates the tension with calculations solely based on current fragmentation. Our findings suggest that, at the energies of existing fixed-target experiments, the separation of current and target fragmentation regions is not distinct. Spin transfer as well as other spin effects offers a sensitive probe into the origin of the produced hadron.

Recent studies suggest that global fits of parton distribution functions (PDFs) might inadvertently “fit away” signs of new physics in the high-energy tails of the distributions measured at the high luminosity program of the LHC (HL-LHC). This could lead to spurious effects that might conceal key beyond the Standard Model (BSM) signatures and hinder the success of indirect searches for new physics. In this paper, we demonstrate that future deep-inelastic scattering (DIS) measurements at the Electron-Ion Collider (EIC), and at CERN via FASERν and SND@LHC at LHC Run III, and the future neutrino experiments to be hosted at the proposed Forward Physics Facility (FPF) at the HL-LHC, provide complementary constraints on large-x sea quarks. These constraints are crucial to mitigate the risk of missing key BSM signals, by enabling precise constraints on large-x PDFs through a “BSM-safe” integration of both high- and low-energy data, which is essential for a robust interpretation of the high-energy measurements.

We have studied the deep inelastic scattering (DIS) of polarized charged leptons from polarized nucleon targets and evaluated the polarized nucleon structure functions g1N,2N(x,Q2), as well as the nucleon asymmetries A1N,2N(x,Q2) for protons and neutrons. The higher-order perturbative corrections up to the next-to-next-to-leading order (NNLO), using the parametrization of polarized parton distribution functions (PPDFs) given by Borsa, Stratmann, Vogelsang, de Florian, and Sassot (BDSSV24) in the three-flavor MS¯ scheme, along with the nonperturbative corrections—namely, the twist-3 corrections and the target mass corrections (TMCs)—have been included in the calculations. The numerical results for the polarized nucleon structure functions, the nucleon asymmetries, and the sum rule integrals of the nucleon structure functions—corresponding to the Ellis-Jaffe, Bjorken, and Burkhardt-Cottingham sum rules—have been evaluated numerically and are found to be in agreement with the experimental results from SLAC, CERN, DESY, and JLab. The benchmarking of the PPDFs of BDSSV24 at NNLO using the present data on polarized nucleon structure functions and other observables will be useful in studying the nuclear medium effects in the scattering of the charged leptons from nuclei at JLab, EIC, DESY, etc., and the scattering of the (anti)neutrinos from polarized nucleons and nuclei at the proposed neutrino factories. Published by the American Physical Society 2025

Abstract The transverse single-spin asymmetry for ρ 0 production in semi-inclusive deep inelastic scattering was recently reported by the COMPASS Collaboration. Using the Sivers function extracted from pion and kaon productions, we perform a calculation of the Sivers asymmetry within the transverse momentum-dependent factorization. Our results are consistent with the COMPASS data, supporting the universality of the Sivers function in the semi-inclusive deep inelastic scattering process for different final-state hadrons within current experimental uncertainties. While different parametrizations of the Sivers function from global analyses allow describing the data equally well, we obtain very different predictions on the Sivers asymmetry of ρ and K * productions at electron-ion colliders, which therefore are expected to provide further constraints.

We extend our prior results on the worldline computation of the axial vector-vector-vector (AVV) triangle anomaly in polarized deeply inelastic scattering (DIS) to the finite mass case by computing in addition the pseudoscalar-vector-vector (PVV) triangle graph. For the well-studied QED case, we show explicitly how the off-forward AVV pole exactly cancels an identical PVV pole. We then demonstrate the dramatic difference in QCD due to the chiral condensate, which qualitatively modifies anomalous Ward identities. As in the massless case, the anomaly pole in QCD is canceled by the dynamics of a primordial isosinglet pseudoscalar η¯-meson, whose Wess-Zumino-Witten coupling to the topological charge density shifts the pole to the physical η′ mass, with the finite quark mass contribution differing by O(10%) from the Witten-Veneziano formula. We obtain a compact analytic expression for the finite mass corrections to Shore and Veneziano’s result that the proton’s net quark helicity ΔΣ∝χQCD′|m=0(0), the forward slope of the topological susceptibility in the chiral limit, and show they are of the order of a few percentages. Our prior prediction that the polarized DIS structure function g1 is quenched by sphaleronlike topological transitions at small x is unaffected by quark mass effects. Our results illustrate how worldline computations of anomalous processes, in synergy with lattice computations and nonet chiral perturbation theory, can uncover novel nonperturbative features of QCD at the Electron-Ion Collider. Published by the American Physical Society 2025

This study presents a comprehensive model for neutrino deep inelastic scattering (DIS) cross sections spanning energies from 50 to 5×1012 GeV with an emphasis on applications to neutrino telescopes. We provide calculations of the total charged-current DIS cross sections and inelasticity distributions up to next-to-next-to-leading order for isoscalar nucleon targets and up to next-to-leading order for nuclear targets. Several modifications to the structure functions are applied to improve the modeling of the cross sections at low energies where perturbative QCD is less accurate and at energies above 104 GeV where there is non-negligible top quark production and small-x logarithms need to be resummed. Using the Fixed-order next-to-leading logarithm (FONLL) general-mass variable-flavor number scheme, we account for heavy quark mass effects and separate the heavy flavor components of the structure functions, obtaining predictions of their relative contributions to the cross sections and the uncertainties arising from the parton distribution functions. Additionally, the effects of final state radiation are implemented in the calculation of the double-differential cross section and discussed in terms of their impact on measurements at neutrino telescopes. Published by the American Physical Society 2025

Using the color dipole picture of deep inelastic scattering (DIS) and the color glass condensate effective theory, we study semi-inclusive jet production in DIS at small x in the limit where the photon virtuality Q^{2} is much larger than the transverse momentum squared P_{⊥}^{2} of the produced jet. In this limit, the cross section is dominated by aligned jet configurations, that is, quark-antiquark pairs in which one of the fermions-the would-be struck quark in the Breit frame-carries most of the longitudinal momentum of the virtual photon. We show that physically meaningful jet definitions in DIS are such that the effective axis of the jet sourced by the struck quark is controlled by its virtuality rather than by its transverse momentum. For such jet definitions, we show that the next-to-leading order cross section admits factorization in terms of the (sea) quark transverse momentum dependent distribution, which in turn satisfies a universal Dokshitzer-Gribov-Lipatov-Altarelli-Parisi and Sudakov evolution.

The study of quantum chromodynamics (QCD) at ultrarelativistic energies can be performed in a controlled environment through lepton-hadron deep inelastic scatterings. In such collisions, the high-energy partonic emissions that follow from the ejected hard partons are accurately described by perturbative QCD. However, the lower energy scales at which quarks and gluons experience color confinement, i.e., hadronization mechanism, fall outside the validity regions for perturbative calculations, requiring phenomenological models tuned to data to describe it. As such, hadronization physics cannot be currently derived from first principles alone. Monte Carlo event generators are useful tools to describe these processes as they simulate both the perturbative and the nonperturbative interactions, with model-dependent energy scales that control parton dynamics. This work employs jets—experimental reconstructions of final-state particles likely to have a common partonic origin—to inspect this transition further. Although originally proposed to circumvent hadronization effects, we show that jets can be utilized as probes of nonperturbative phenomena via their substructure. The charge correlation ratio was recently shown to be sensitive to hadronization effects. Our work further improves this sensitivity to nonperturbative scales by introducing a new selection based on the relative placement of the within the clustering tree, defined as the unclustering that resolves the jet’s leading charged particles. Published by the American Physical Society 2025

We develop the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution of the Deep Inelastic Scattering (DIS) structure functions at next-to-leading order (NLO) in α s , formulated directly in terms of the structure functions rather than parton distribution functions (PDFs). We refer to this framework as the physical-basis approach. First, we express the NLO PDFs in terms of the structure functions in momentum space. Substituting these expressions into the DGLAP equations, we derive the evolution equations in the physical basis. We demonstrate that, within this approach, the evolution equations are independent of the choice of factorization scale and scheme. Finally, we discuss the application of the NLO physical basis in calculation of LHC cross sections.

Deep-inelastic Scattering with Collider Neutrinos at the LHC and Beyond

We study the helicity correlation of two Lambda hyperons produced in unpolarized semi-inclusive deep inelastic scatterings (SIDIS), with one hyperon detected in the current fragmentation region and the other in the target fragmentation region. This observable provides direct access to the spin-dependent fragmentation function G_{1Lq} and the spin-dependent fracture function l_{1q}^L even in unpolarized lepton nucleon collisions. Utilizing the perturbative matching of the fracture function, we present numerical predictions for the helicity correlation, revealing significant variations with flavor and kinematic regions. This observable offers a unique way to investigate the spin-dependent hadronization mechanism across both the current and target fragmentation regions. It also provides new insights into the spin transfer effects in SIDIS processes.

We compute the inclusive dihadron cross-section in Deep Inelastic Scattering at next-to-leading order (NLO) and small x in the Color Glass Condensate. We focus on the kinematic limit where the hadrons are produced at forward rapidities (in the direction of the virtual photon) and back-to-back in the transverse plane. Our calculation demonstrates that the coefficient of the Sudakov double logarithm for this process is −αs2πCF+Nc2 instead of −αsNc4π when back-to-back jets are measured in the final state. To preserve the universality of the Sudakov soft factor associated with the Weizsäcker-Williams transverse momentum dependent (TMD) gluon distribution, we promote the collinear fragmentation functions into TMD fragmentation functions. We then perform the resummation of the Sudakov logarithms through Collins-Soper-Sterman evolution of the TMD fragmentation functions and the Weizsäcker-Williams TMD gluon distribution. Finally, analytic expressions are obtained for the NLO coefficient functions in the MS¯-scheme. These results pave the way towards numerically calculating dihadron correlations at small x at the future Electron-Ion Collider with full NLO accuracy.

Fragmentation functions (FFs) are essential nonperturbative QCD inputs for predicting hadron production cross sections in high energy scatterings. In this study, we present a joint determination of FFs for light charged hadrons through a global analysis at next-to-leading order (NLO) in QCD. Our analysis incorporates a wide range of precision measurements from the LHC, as well as data from electron-positron collisions and semi-inclusive deep inelastic scatterings. By including measurements of jet fragmentation at the LHC in our global analysis, we are able to impose strong constraints on the gluon FFs. A careful selection of hadron kinematics is applied to ensure the validity of factorization and perturbative calculations of QCD. In addition, we introduce several methodological advances in fitting, resulting in a flexible parametrization form and the inclusion of theoretical uncertainties from perturbative calculations. Our best-fit predictions show very good agreement with the global data, with χ2/Npt∼0.90. We also generate a large number of Hessian error sets to estimate uncertainties and correlations of the extracted FFs. FFs to charged pions (kaons and protons) are well constrained for momentum fractions down to 0.01 (0.1). Total momentum of partons carried by light charged hadrons are determined precisely. Their values for u, d quarks and gluon saturate at about 50% for a lower cut of the momentum fraction of 0.01. Comparing our determinations to results from other groups, we find significant discrepancies, particularly for the proton fragmentation functions, as well as for gluon and unfavored quarks to pions and kaons. Pulls from individual datasets and impact of various choices of the analysis are also studied in details. Our analysis raises questions concerning existing and future experimental measurements, including the need for clarifications on the definitions of various hadron final states and the necessity of further measurements on fragmentation from heavy quarks. Additionally, we present an update of the program used for calculating hadron production cross sections. We demonstrate the broad applications of the program combined with our new FFs, including NLO predictions on jet charges in proton collisions and reference cross sections for heavy-ion collisions, which show good agreement with LHC data. Our FFs, including the error sets (denoted as NPC23), are publicly available in the form of LHAPDF6 grids. Published by the American Physical Society 2024

In this Letter, we propose a new experimental method to check the contribution of the chiral magnetic effect (CME). With experimental data of deep inelastic scattering (DIS) involving transversely polarized proton, we have calculated the three-dimensional charge density inside the polarized proton, which is found to have a significant violation to spherical symmetry. Then we have calculated the property of electromagnetic field (EM field) generated by a single transversely polarized proton (p↑). Based on them, the EM fields generated in small collision system p↑+A are studied. We find that the orientation of this EM field has a significant dependence on the polarization direction of the proton, and the correlator (Δγ) has also significant dependence on the angle between the reaction plane and polarization direction. As background contributions are canceled comparing two collision geometry schemes, only the contribution of CME remains. Published by the American Physical Society 2024