arXiv subjects

João M. Silva

Publications and source records attributed to João M. Silva.

11 recordsLinked to original sources

arXiv2026

Quantum simulating multi-particle processes in high energy nuclear physics: dijet production and color (de)coherence

Hard scattering events in high-energy collisions produce highly virtual partons that subsequently fragment into collimated hadronic cascades. When such partonic showers evolve in a QCD medium, as in deep-inelastic scattering or heavy-ion collisions, the resulting multi-particle distributions encode information about the surrounding matter. Decades of theoretical developments have led to a consistent and order-by-order improvable perturbative description of the shower. This description needs, however, the non-perturbative input that encodes the structure of the hadronic matter. The determination of such input remains challenging within conventional computational approaches, thereby limiting the applicability of the approach. In this work, we develop a framework that employs quantum simulation techniques to compute multi-particle processes in such environments by mapping partonic cross-sections to quantum circuits. As benchmarks, we analyze dipole formation and the QCD antenna radiation pattern at leading order in the strong coupling constant, comparing the results with analytic estimates in simplified limits. The quantum circuit formulation here introduced naturally extends to higher perturbative orders and enables amplitude-level computations in complex matter backgrounds. This provides a systematic foundation for applying quantum information science methods to study multi-particle dynamics in QCD media.

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arXiv2026

Hydrodynamics and Energy Correlators

We study energy-energy correlators (EECs) in many-body quantum states, focusing on the matter produced in the aftermath of heavy-ion collisions. We analyze the angular structure of EECs in the collinear limit and identify a sequence of dynamical regimes. At the largest angular separations within the small-angle regime, the observable is dominated by disconnected contributions, leading to a classical scaling determined by the collective flow of the medium. We explicitly construct this contribution for hadrons produced from a hydrodynamic medium described by boost-invariant Gubser flow, obtaining the angular dependence of the EEC analytically. We further consider azimuthal perturbations to this flow, illustrating how EECs can be used to probe anisotropies in the initial state. At smaller angular separations, connected contributions become increasingly important. We argue that in this regime the EEC is controlled by collective hydrodynamic modes. The resulting angular behavior is similar to the one identified in the EECs of heavy and large-charge states of conformal field theories. At even smaller angles, this regime is expected to match onto the structure determined by the light-ray operator product expansion, before eventually crossing over to the smallest-angle behavior characteristic of dilute hadronic matter. Altogether, these results provide a unified picture of the angular structure of EECs in many-body QCD states and suggest new observables sensitive to the properties of matter in heavy-ion collisions.

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arXiv2025

Early-Time Dynamics of Heavy-Ion Collisions through Energy Correlators: celestial blocks and the spacetime structure of out-of-equilibrium QCD matter

Ultrarelativistic heavy-ion collisions provide a unique window into far-from-equilibrium states of QCD matter. The initial stages of these events are characterized by highly anisotropic, nonthermal dynamics that precede hydrodynamization, yet they remain largely inaccessible through conventional soft observables. In this work, we show that the substructure of mid-rapidity jets provides direct sensitivity to the spacetime structure of this early, anisotropic phase. Using classical Yang-Mills simulations and effective kinetic theory to model the early-time evolution of the jet quenching parameter, we compute the azimuthally differential energy-energy correlator within the BDMPS-Z framework. By decomposing the result into celestial blocks, we isolate the coefficients that encode the anisotropic geometry and dynamics of the underlying medium. We identify an observable that couples directly to spatial anisotropies in the out-of-equilibrium QCD matter and also discuss the impact of medium response on its behavior. We further extend our study to mid-rapidity jets generated with the JEWEL Monte-Carlo, adjusted to incorporate an anisotropic medium background, and find qualitative agreement with the analytical expectations. Finally, we discuss how higher-point energy correlators and generalized energy-flow operators can enhance the sensitivity to the microscopic structure of far-from-equilibrium QCD matter.

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arXiv2025

QCD antenna radiative spectrum in dense media within the Improved Opacity Expansion

We compute the double differential inclusive spectrum for the emission of a soft gluon from a color-singlet $q\bar q$ pair traversing a dense QCD medium. Our results extend the existing literature by simultaneously incorporating both single hard and multiple soft gluon exchanges between the jet and the medium -- an essential ingredient for a complete phenomenological description of jet quenching. Using the Improved Opacity Expansion framework, we provide an analytically tractable treatment, reducing the full cross-section to a set of simple expressions. Our analysis demonstrates that rare hard (Molière) scatterings significantly modify the gluon spectrum at large angles, accelerating the loss of color coherence between the initial quarks. We further quantify whether the modifications are driven by an overall weakening of the interference term, or by more detailed modifications to the fragmentation pattern. Our results provide a direct input for phenomenological jet quenching studies, offering new insights into the role of color decoherence in QCD matter.

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arXiv2025

Collinear spin correlations of final-state radiation in dense QCD matter

Spin correlations are required to reproduce the correct azimuthal dependence of matrix elements for successive branchings at disparate angles in QCD jets. In this paper, we study modifications to this, $\cos(2ψ_{12})$, azimuthal pattern in the presence of a quark-gluon plasma. To that end, we consider a simplified setup in which a narrow and energetic QCD antenna is formed inside a medium of fixed length and radiates a collinear emission outside it. The calculation includes both light and heavy-quarks. Further, we do not include medium-induced spin-flip interactions since they are energy suppressed in our formalism. We show that the amplitude of the azimuthal modulation in the presence of a medium is always suppressed with respect to the vacuum baseline, with its magnitude depending on the medium properties and splitting kinematics. For a medium with a momentum space anisotropy, we find that the azimuthal modulation acquires a phase shift, i.e., $\cos(2ψ_{12}) \to \cos(2ψ_{12}+ϕ_{\rm med })$, where $ϕ_{\rm med}$ is a process-dependent function that again depends on the medium properties and splitting kinematics. This work provides theory guidance for implementing spin-driven interference effects in phenomenological studies of jet quenching in heavy-ion collisions.

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arXiv2025

Heavy Quark Pair Energy Correlators: From Profiling Partonic Splittings to Probing Heavy-Flavor Fragmentation

We introduce heavy-flavor energy correlators, $\langle Ψ|\mathcal{E}_{\mathcal{H}}(\vec{n}_1) \mathcal{E}_{\mathcal{H}}(\vec{n}_2)|Ψ\rangle$, as a powerful observable for profiling partonic splittings and characterizing heavy-flavor fragmentation. We present its collinear factorization, perform resummation, and demonstrate the angular distribution's sensitivity to both the heavy-quark pair splitting and their subsequent fragmentation. We then apply the heavy-flavor EEC to probe medium-induced effects, revealing its sensitivity to medium modifications to heavy-quark pair splitting functions and to the medium's spatial structure.

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arXiv2025

Dissecting Jet Modification in the QGP with Multi-Point Energy Correlators

Energy correlators have recently attracted significant attention in the study of heavy ion collisions due to their potential to robustly connect experimental measurements with an underlying quantum field theoretic description. While theoretical studies have so far primarily focused on the simplest two-point correlator, mapping out the dynamics of the quark-gluon plasma (QGP) will require developing a theoretical understanding of multi-point energy correlators. In this paper we present a systematic theoretical study of multi-point energy correlators for jets fragmenting in a dense quark-gluon plasma, accounting for both the medium's perturbative modification to the jet, and its hydrodynamical back-reaction. We consider both the scaling behavior of projected correlators, as well as the shape dependent three-point correlator, highlighting how both provide insight into interactions with the QGP. We discuss the parametric dependence of modifications on the medium scales, opening new opportunities to experimentally separate jet modifications from the medium response. Our results open the door to a systematic exploration of multi-point energy correlators in heavy ion collisions.

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arXiv2024

Towards an unbiased jet energy loss measurement

The modifications imprinted on jets due to their interaction with Quark Gluon Plasma (QGP) are assessed by comparing samples of jets produced in nucleus-nucleus collisions and proton-proton collisions. The standard procedure ignores the effect of bin migration by comparing specific observables for jet populations at the same reconstructed jet transverse momentum ($p_T$). Since jet $p_T$ is itself modified by interaction with QGP, all such comparisons confound QGP induced modifications with changes that are simply a consequence of comparing jets that started out differently. The quantile matching procedure introduced by Brewer et al. directly estimates average fractional jet energy loss ($Q_{AA}$) and can thus mitigate this $p_T$ migration effect. In this work, we validate the procedure in more realistic scenarios that include medium response. We study the evolution of $Q_{AA}$ with jet radius, its sensitivity to minimum particle $p_T$ and medium response as implemented in two different models for jet evolution in heavy-ion collisions. Further, we use this procedure to establish that the difference between inclusive jet and $γ+$jet nuclear modification factors ($R_{AA}$) is dominated by differences in the spectral shape, leaving the colour charge of the jet initiating parton with a lesser role to play. Additionally, we compare $Q_{AA}$ to an experimentally proposed proxy for fractional jet energy loss, $S_{loss}$, showing that both quantities are similar, although the former provides a more clear physical interpretation. Finally, we show the size of the $p_T$ migration correction for four different substructure observables and how to reliably use the quantile procedure experimentally to improve existing measurements.

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arXiv2024

Tracking Energy Loss in Heavy Ion Collisions

The main modification to high $p_t$ jets evolving in the quark gluon plasma is the depletion of their energy to the thermal background. Despite the prominent role played by energy loss effects in jet quenching, their theoretical description is still limited, being, to a large extent, driven by phenomenological considerations. As the field moves towards the measurement of multi-scale jet substructure observables, it is necessary to develop new field theoretic techniques to describe energy loss. In this letter, we highlight a formal similarity between energy loss, and the renormalization group based track function formalism for computing jet substructure observables on charged particles. We introduce an energy loss function, $L_i(x)$, tracking the energy fraction $x$ flowing from an initial hard parton $i$ down to the measured hadrons, and show that its renormalization group evolution can be studied in perturbative QCD, and is related to that of the track functions. The features of this new approach are illustrated in the computation of projected energy correlators, opening the window to a better theoretical treatment of these observables in heavy ion collisions.

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arXiv2024

Gluon to $q\bar q$ antenna in anisotropic QCD matter: spin-polarized and azimuthal jet observables

We study the production of a quark-antiquark antenna in the presence of a dense and anisotropic QCD medium. We assume the antenna to originate from an unpolarized gluon state, and consider both massless and massive final states. The medium anisotropy is captured by allowing the jet quenching coefficient to take different magnitudes in orthogonal directions with respect to the jet axis. We find that the final particle distribution is sensitive to the medium anisotropy, and more importantly, that this effect couples directly to the helicity/spin of the final states. We propose to look into these effects by performing a Fourier decomposition of the particle distribution inside the jet. In our medium model, we find that the spin independent terms contribute to the even harmonics of the cosine series. The helicity/spin dependence enters only through the sine Fourier series. We further explore the spin dependence by examining the degree of polarization of the final states in different directions. Our results indicate that the anisotropies present in the QCD matter produced in heavy ion collisions can be probed by studying azimuthal and spin observables inside jets.

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arXiv2021

On mass generation in Landau-gauge Yang-Mills theory

A longstanding question in QCD is the origin of the mass gap in the Yang-Mills sector of QCD, i.e., QCD without quarks. In Landau gauge QCD this mass gap, and hence confinement, is encoded in a mass gap of the gluon propagator, which is found both in lattice simulations and with functional approaches. While functional methods are well suited to unravel the mechanism behind the generation of the mass gap, a fully satisfactory answer has not yet been found. In this work we solve the coupled Dyson-Schwinger equations for the ghost propagator, gluon propagator and three-gluon vertex. We corroborate the findings of earlier works, namely that the mass gap generation is tied to the longitudinal projection of the gluon self-energy, which acts as an effective mass term in the equations. Because an explicit mass term is in conflict with gauge invariance, this leaves two possible scenarios: If it is viewed as an artifact, only the scaling solution survives; if it is dynamical, gauge invariance can only be preserved if there are longitudinal massless poles in either of the vertices. We find that there is indeed a massless pole in the ghost-gluon vertex, however in our approximation with the assumption of complete infrared dominance of the ghost this pole is only present for the scaling solution. We also put forward a possible mechanism that may reconcile the scaling solution, with an infrared dominance of the ghost, with the decoupling solutions based on longitudinal poles in the three-gluon vertex as seen in the PT-BFM scheme.

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