We compute non-eikonal corrections to dijet production in deep inelastic scattering off a nucleus. Such corrections are expected to be quantitatively important at the energies of the future Electron Ion Collider. We focus on those corrections stemming solely from the finite longitudinal size of the nucleus. For both longitudinally and transversely polarized photons, we provide general, all-order expressions in terms of two-dimensional path integrals. To proceed further, we use the harmonic oscillator approximation for the target averages of Wilson lines. We then expand the general expressions order by order beyond the shockwave limit which provides the eikonal results, up to next-to-next-to-eikonal accuracy. We observe that next-to-eikonal corrections to this observable vanish for the mentioned approximation for target averages, as previously found for single gluon production in proton-nucleus collisions. Finally, we calculate the back-to-back of correlation limit of our expressions.

The spectrum of coherent gluon radiation from a quark-anti-quark pair experiencing multiple scatterings within a coloured medium is central for understanding in-medium parton cascades. Despite its foundational importance, current results are limited by reliance on simplified scattering rates, such as the harmonic oscillator approximation, valid only in restricted phase-space regions. Using the formalism introduced in [1], we express the gluon emission spectrum as a set of differential equations that can be solved numerically, circumventing conventional approximations. We present the transverse momentum and energy distributions of emitted gluons for realistic interaction models, illustrating the breakdown of colour coherence across the entire accessible phase-space, and consequently enabling a higher-precision description of jet observables.

We develop a Gaussian model to evaluate the decorated dipole and quadrupole operators that arise beyond the eikonal approximation in the Color Glass Condensate framework. While the method is general and applicable to arbitrary beyond-eikonal Wilson line structures, we employ it for dijet production in deep inelastic scattering at next-to-eikonal accuracy. After validating the model at the eikonal level, we compute all next-to-eikonal operator structures entering the dijet cross section. We show that some of them do not contribute to this observable, while others vanish identically. Therefore, in the Gaussian model next-to-eikonal corrections to dijet production in deep inelastic scattering originate solely from a given type of operators and from next-to-eikonal three-point correlators. The resulting expressions are provided in a form suitable for numerical implementation.

We explore the recently derived equation that resums DGLAP corrections to the JIMWLK Hamiltonian in the simplified setting of the SU(2) gauge theory. We solve the equation numerically for the scattering matrix of a dressed gluon for a particular initial condition, that corresponds to a dipole initial state. We evolve the S-matrix of a single dressed gluon from the scale QP, which is the inverse color correlation length in the projectile to Q ≫ QP which corresponds to the hard resolution scale provided by the target. As expected, S ceases to be unitary if evolved to significant ln Q^2/Q_P^2 . Our numerical results indicate an interesting universal (independent of the coupling constant) pattern for this deviation from unitarity.

The internal structure of the exotic meson X(3872) remains an open question. We investigate its production in heavy-ion collisions under the hypothesis that it is a compact tetraquark. To this end, we derive a coalescence model from the Lindblad equation, assuming that unbound heavy quarks are thermalized within the quark-gluon plasma and that the adiabatic approximation holds. Using this model, we predict the nuclear modification factor of the X(3872) at LHC energies, with proton-proton baseline cross sections estimated from available experimental data. We also consider the effect of simplifying assumptions on the model, and a complementary approach based on chemical equilibration. Our results indicate that recombination is the dominant production mechanism for a tetraquark X(3872). It leads to a significant yield enhancement in heavy-ion collisions, suggesting that the nuclear modification factor is a powerful observable for probing the exotic nature of this state

The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisioned for the near-, mid-, and long-term future. All submitted contributions are evaluated by the Physics Preparatory Group (PPG), and a preliminary analysis is presented at a Symposium meant to foster a broad community discussion on the scientific value and feasibility of the various ideas proposed. The outcomes of the analysis and the deliberations at the Symposium are synthesized in the current Briefing Book, which provides an important input in the deliberations of the Strategy recommendations by the European Strategy Group (ESG).

We study the potential of X(3872) at finite temperature in the Born-Oppenheimer approximation under the assumption that it is a tetraquark. We argue that, at large number of colors, it is a good approximation to assume that the potential consists in a real part plus a constant imaginary term. The real part is then computed adapting an approach by Rothkopf and Lafferty and using as input lattice QCD determinations of the potential for hybrids. This model allows us to qualitatively estimate at which temperature range the formation of a heavy tetraquark is possible, and to propose a qualitative picture for the dissociation of the state in a medium. Our approach can be applied to other suggested internal structures for the X(3872) and to other exotic states.

We present a systematic study of how different choices of ordering and phase-space constraints in parton showers affect the space-time structure of vacuum parton cascades and their interface with jet quenching models. Using a simplified Monte Carlo shower implemented at double logarithmic accuracy, we analyse variations in emission patterns and resulting phase-space arising from three ordering variables: inverse formation time, invariant mass, and opening angle. These are coupled with two kinematic reconstruction schemes defined by different phase-space constraints. We show that, while global features are relatively stable, differences emerge in the temporal evolution of the cascade. To probe the impact of these differences, we introduce a simplified model for in-medium energy loss based on formation time and colour decoherence, enabling us to evaluate the sensitivity of quenching observables to the underlying space-time structure of the vacuum shower. We further quantify the role of time-ordering violations and propose strategies to preserve a consistent space-time interpretation. Lastly, we explore a range of alternative quenching models confirming the robustness of our conclusions. Our findings highlight the importance of maintaining a coherent space-time structure in parton shower algorithms when modelling jet propagation in an extended QCD medium, as this structure becomes a physically meaningful and testable component of the jet itself.

The assumption of factorization lies at the core of calculations of medium effects on observables computable in perturbative Quantum Chromodynamics. In this work we examine this assumption, for which we propose a setup to study hard processes and bulk nuclear matter in heavy-ion collisions on the same footing using the Glauber modelling of heavy nuclei. To exemplify this approach, we calculate the leading-order corrections to azimuthal decorrelation in Drell-Yan and boson-jet processes due to cold nuclear matter effects, not considering radiation. At leading order in both the hard momentum scale and the nuclear size, the impact-parameter dependent cross section is found to factorize for both processes. The factorization formula involves a convolution of the hard cross section with the medium-modified parton distributions, and, for boson-jet production, the medium-modified jet function.

This paper assesses the uncertainties inherent to parton shower simulations at double logarithmic accuracy, with a focus on their impact on jet quenching studies in high-energy heavy-ion collisions. For that purpose, we developed a massless quark-initiated vacuum parton shower toy-model with different evolution variables, such as inverse formation time, invariant squared mass, and squared opening angle. In addition to the effects of varying the ordering variable we further examine their corresponding kinematic reconstructions. The results highlight how these variations influence key distributions, including the number of splittings, angular and transverse momentum distribution of subsequent emissions. We also analyse the Lund distributions and their average trajectories, revealing that the choice of ordering variable has a significantly greater impact on the vacuum parton shower evolution than the kinematic scheme, particularly in large-angle emission regions. When a simple jet quenching model based on decoherence is implemented, we observe that the fraction of quenched events is sensitive to the ordering prescription, especially for the first splitting and thin media, highlighting the need for a deeper understanding of the branching process in the presence of an extended QCD media.

A study is presented of the impact of simulated inclusive Electron Ion Collider Deep Inelastic Scattering data on the determination of the proton and nuclear parton distribution functions (PDFs) at next-to-next-to-leading and next-to-leading order in QCD, respectively. The influence on the proton PDFs is evaluated relative to the HERAPDF2.0 set, which uses inclusive HERA data only, and also relative to the global fitting approach of the MSHT20 PDFs. The impact on nuclear PDFs is assessed relative to the EPPS21 global fit and is presented in terms of nuclear modification ratios. For all cases studied, significant improvements in the PDF uncertainties are observed for several parton species. The most striking impact occurs for the nuclear PDFs in general and for the region of high Bjorken $x$ in the proton PDFs, particularly for the valence quark distributions.

We investigate the determination of the partonic structure of colorless exchanges in deep inelastic diffractive ep scattering at the Electron Ion Collider, using the standard decomposition into Pomeron and Reggeon contributions. We perform fits to simulated diffractive cross section pseudodata in four variables, including the momentum transfer t, to estimate the achievable precision on the Pomeron and Reggeon quark and gluon distributions. We analyze the influence of different cuts in the kinematic variables, beam energy configurations and luminosities, including a `first year' scenario. We conclude that the EIC will be able to constrain the partonic structure of the sub-leading Reggeon exchange with a precision comparable to that of the leading Pomeron exchange.

Abstract We analyze the effects of next-to-eikonal corrections on dijet production in Deep Inelastic Scattering off nuclear targets in the framework of the Color Glass Condensate. They require the knowledge of correlators of fields in the target beyond those computed in the standard McLerran-Venugopalan model, specifically those between transverse and boost-enhanced components, and of the recoil of the fields. We neglect the latter, while for the former we develop a linear model valid for large nuclei. We considered the unpolarized cross sections for dijet production in the approximation of a homogenous dilute nucleus, obtaining simple analytic expressions for the cross sections at next-to-eikonal accuracy, valid in the limit of total dijet momentum and dijet momentum imbalance larger than the saturation scale of the nucleus. We perform a numerical study of the results at energies of the Electron Ion Collider, finding $$ \mathcal{O} $$ O (10%) effects in the cross sections at large total momentum. We also analyze the azimuthal asymmetries between total momentum and imbalance, finding that non-eikonal corrections induce odd azimuthal harmonics for the situation of jets with equal momentum fractions from the virtual photon, where they are absent in the eikonal approximation. Finally, in the eikonal approximation we have compared the results of our analytic expansion valid in the dilute limit of the target, and the full Color Glass Condensate results in the McLerran-Venugopalan model and their correlation limit. Our analytic expressions match the correlation limit ones in the region where both should be simultaneously valid and reproduce very well the full Color Glass Condensate results in its validity region.

The theoretical treatment of jet quenching lacks a full description of the interplay between vacuum-like emissions, usually formulated in momentum space, and medium induced ones that demand an interface with a space-time picture of the expanding medium and thus must be formulated in position space. In this work we build a toy Monte-Carlo parton shower ordered in formation time, virtual mass, and opening angle, which are equivalent at leading logarithmic accuracy. Aiming to explore a link with jet substructure, we compute the Lund plane distributions for the different ordering prescriptions. Further, we investigate the sensitivity of ordering prescriptions to medium effects by counting the number of events eliminated by a decoherence condition.

Particle correlations in small collisions systems, like proton–nucleus, lie at the core of the discussion about whether quark–gluon plasma is produced in small systems. Both initial and final state explanations have been essayed to describe such correlations. In this work, we focus on the initial state explanations provided by the quantum effects in the initial wave function of the incoming hadrons, in the framework of the Color Glass Condensate effective theory. We describe the formalism indicating the different inputs required for phenomenological applications. We compare the results from two different models, finding that the results for azimuthal harmonics agree qualitatively, but show quantitative differences, particularly at transverse momenta above the saturation scale.

The Future of the Large Hadron Collider, pp. 321-335 (2023) Open AccessChapter 23: Electron-Hadron Scattering resolving Parton DynamicsNéstor Armesto, Claire Gwenlan, and Anna StastoNéstor ArmestoInstituto Galego de Física de Altas Enerxías IGFAE, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia-Spain, Spain, Claire GwenlanDepartment of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford. OX1 3RH., United Kingdom, and Anna StastoDepartment of Physics, The Pennsylvania State University, University Park, PA 16802, U.S.A.https://doi.org/10.1142/9789811280184_0023Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The following sections are included: Resolving the Dynamics of Partons in Protons and Nuclei Diffractive scattering and three dimensional structure Small-x dynamics References FiguresReferencesRelatedDetails Recommended The Future of the Large Hadron ColliderMetrics History Information© The Author(s)This is an open access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC BY) License.PDF download

In this contribution we reconsider the calculation at next-to-leading order of forward inclusive single hadron production in $pA$ collisions within the hybrid approach. We conclude that the proper framework to compute this cross section beyond leading order is not collinear factorization as assumed so far, but the TMD factorized framework.