Chien-Peng Yuan

A correction to this paper has been published: https://doi.org/10.1007/JHEP02(2026)244

A bstract: We initiate a systematic study of fragmentation energy correlators (FECs), which generalize traditional fragmentation functions and encode non-perturbative information about transverse dynamics in parton fragmentation processes. We define boost-invariant, non-perturbative FECs and derive a corresponding collinear factorization formula. A spin decomposition of the FECs is carried out, analogous to that of transverse-momentum-dependent fragmentation functions. In this work we focus particularly on the Collins-type quark FEC, which is sensitive to chiral symmetry breaking and characterizes the azimuthal asymmetry in the fragmentation of a transversely polarized quark. We perform a next-to-leading-order calculation of the corresponding hard coefficient in semi-inclusive deep-inelastic scattering for the quark non-singlet component, thereby validating the consistency of our theoretical framework.

The Hessian method is widely applied in the global analysis of parton distribution functions (PDFs), which use a set of orthogonal eigenvectors to give predictions of a physical observable. Its uncertainty is estimated based on the assumption that all physical observables can be approximately expressed as linear functions of the nonperturbative parameters in PDF. In this article, we report an improved Hessian method which takes the nonlinear effects into account in the uncertainty estimation. A pseudoglobal analysis is designed to numerically test the new method. The nonlinear uncertainties can significantly enlarge the original linear ones. Such uncertainties can be reduced with high precision data introduced into the global analysis. However, the nonlinear effect could still be sizable corresponding to the current precision of the experimental measurements.

We propose to probe light-quark dipole interactions at lepton colliders using the azimuthal asymmetry of a collinear dihadron pair ( h 1 h 2 ) produced in association with another hadron h ′ . This asymmetry, arising from quantum interference in the quark spin space, is exclusively sensitive to dipole interactions at the leading power of the new physics scale and simultaneously probes both the real and imaginary components of the dipole couplings. By combining all possible channels of h ′ , this method allows for disentangling the up and down quark dipole moments and has the potential to significantly strengthen current constraints by one to two orders of magnitude.

Parton distribution functions (PDFs) form an essential part of particle physics calculations. Currently, the most precise predictions for these nonperturbative functions are generated through fits to global data. A problem that several PDF fitting groups encounter is the presence of tension in datasets that appear to pull the fits in different directions. In other words, the best fit depends on the choice of dataset. Several methods to capture the uncertainty in PDFs in presence of seemingly inconsistent fits have been proposed and are currently in use. These methods are important to ensure that uncertainty in PDFs are not underestimated. Here we propose a novel method for estimating the uncertainty by introducing a generalized statistical model based on Bayesian hierarchical models, which is implemented via the Gaussian Mixture Model (GMM). The methodology is inspired by unsupervised machine learning techniques and is closely related to the statistical methods of ensemble learning and Bayesian model averaging. Using a toy model of PDFs, we demonstrate how the GMM can be used to faithfully reconstruct the likelihood associated with PDF fits, which can in turn be used to accurately determine the uncertainty on PDFs, especially in the presence of tension in the fitted datasets. We further show how this statistical model reduces to the usual χ 2 likelihood function for a consistent dataset and provide measures to optimize the number of Gaussians in the GMM.

The violation of the Lam-Tung relation in the high- p T ℓ ℓ region of the Drell-Yan process at the LHC presents a longstanding discrepancy with the standard model prediction at O ( α s 3 ) accuracy. In this paper, we employed a model-independent analysis to investigate this phenomenon within the framework of the standard model effective field theory (SMEFT). Our findings revealed that the leading contributions from SMEFT to this violation appear at the 1 / Λ 4 order with O ( α s ) accuracy in quantum chromodynamics (QCD) interaction. Notably, we demonstrated that the quadratic effect of dimension-6 dipole operators, associated with the Z boson, dominates the breaking effects induced by various dimension-6 and dimension-8 operators. This provides a possible explanation for the observed discrepancy with the Standard Model predictions at the LHC. Furthermore, the breaking effects could also serve as a powerful tool for constraining Z -boson dipole interactions, highlighting their importance among potential sources of new physics in the Drell-Yan process. Published by the American Physical Society 2025

The resummation calculation (esos) is a widely used tool for the simulation of single vector boson production at colliders. In this work, we develop a significant improvement over the esos code by increasing the accuracy from NNLL + NLO to N 3 LL + NNLO and release the esos v2.0 code. Furthermore, we propose a new nonperturbative function that includes information about the rapidity of the system (IFY). The IFY functional form was fitted to data from fixed target experiments, the Tevatron, and the LHC. We find that the nonperturbative function has mild rapidity dependence based on the results of the fit. Published by the American Physical Society 2024