Transverse momentum dependent (TMD) parton distribution functions: status and prospects (1507.05267v1)

Abstract: We provide a concise overview on transverse momentum dependent (TMD) parton distribution functions, their application to topical issues in high-energy physics phenomenology, and their theoretical connections with QCD resummation, evolution and factorization theorems. We illustrate the use of TMDs via examples of multi-scale problems in hadronic collisions. These include transverse momentum q_T spectra of Higgs and vector bosons for low q_T, and azimuthal correlations in the production of multiple jets associated with heavy bosons at large jet masses. We discuss computational tools for TMDs, and present an application of a new tool, TMDlib, to parton density fits and parameterizations.

• The paper demonstrates the necessity of TMD parton distribution functions in addressing low-qT dynamics and high-energy factorization beyond collinear approximations.
• It employs QCD resummation, evolution equations, and computational tools to refine predictions in processes like Drell-Yan and Higgs production.
• The study underscores the integration of theoretical TMD frameworks with experimental data, paving the way for enhanced precision in collider-based analyses.

Overview of "Transverse momentum dependent (TMD) parton distribution functions: status and prospects"

The paper "Transverse Momentum Dependent (TMD) Parton Distribution Functions: Status and Prospects" provides a detailed examination of TMD parton distribution functions within the context of Quantum Chromodynamics (QCD) and their applications to high-energy physics phenomenology. The authors explore theoretical underpinnings related to QCD resummation, evolution, and factorization theorems, while also highlighting practical aspects through computational tools and experimental implications.

Theoretical Context and Motivation

The authors explore the necessity of TMD parton distribution functions in extending the analyses of high-energy and multi-scale problems in hadronic collisions beyond the conventional collinear factorization approach. They emphasize two primary scenarios where TMDs offer significant insights:

1. Low-$q_T$ Dynamics: In processes such as Drell-Yan hadroproduction of electroweak gauge bosons, TMDs are essential for correctly modeling the behavior as $q_T$ approaches zero. Conventional perturbation theory diverges in this limit, necessitating a factorization approach that captures the full dynamics of gluon and quark transverse momentum distributions intricately linked with polarization.
2. High-energy Factorization: This applies when $\sqrt{s}$ is large, and momentum transfer remains fixed, as seen in scenarios including deeply inelastic scattering where large logarithmic corrections arise from higher-order loop contributions within QCD.

Implementation and Analysis

The paper highlights computations involving TMDs, illustrated through transverse momentum distributions and azimuthal correlations, particularly in the context of hadronic collisions producing Higgs, vector bosons, and associated jets. The authors provide a sophisticated treatment of the evolution equations that govern TMDs, building upon the foundational QCD renormalization group framework.

Furthermore, they discuss the computational tools available for TMD analysis, specifically showcasing applications that use these advanced computational techniques to perform parton density fits and parameterizations. By employing resummations these tools can incorporate a broad set of experimental data, thereby connecting theory with phenomenological predictions.

Experimental and Future Directions

Experimental prospects extend these theoretical formulations to real-world collider data. The authors underscore the importance of precise measurements of cross-sections at varying scales of $q_T$, exploring the differences between regions of high and low momentum transfer. The focus on practical applications is evident, as the paper posits that improved precision in the determination and evolution of TMDs could significantly enhance the accuracy of predictions for LHC data, Tevatron outputs, and polarized scatterings.

The paper briefly touches on Monte Carlo event generators augmented with TMD dynamics, calling for further development in this area to integrate theoretical TMD frameworks with full event simulation, enhancing the TMD predictions to an experimental environment.

Concluding Remarks

In closing, the authors advocate for a deeper integration of TMDs into the toolkit of high-energy phenomenology, stressing their role in bridging existing gaps between theory and experiment. The focus on creating robust parameterizations and fitting methods applicable across a diverse set of scattering processes highlights a path forward in improving the accuracy of the first-principle QCD predictions. The continuous refinement of computational methods and the development of accessible libraries of TMDs for diverse applications remain central to these efforts. This work represents a pivotal step in advancing the understanding of partonic structures and interactions at fine granularities in terms of both theoretical and practical contributions to high-energy physics.