Programme Synopsis

The strong interaction and its quantum field theory (QFT) description by virtue of Quantum Chromodynamics (QCD), an SU(3) gauge theory, are at the center point of all scattering reactions at particle colliders such as the Large-Hadron-Collider (LHC). Making reliable and accurate predictions for experimentally accessible S-matrix elements and cross sections is the foundation of acquiring access to the more subtle electroweak effects ($Z$, $W^\pm$, photons, Higgs particle) and to potential effects of physics beyond the Standard Model. Essential QCD properties that permeate all its applications are the asymptotic freedom and the fact that the gluons, the QCD gauge bosons, are massless. Asymptotic freedom dictates by the QCD renormalization group flow that the QCD gauge coupling $\alpha_s$ is small at very high energies, where perturbative methods can be employed, but large and non-perturbative at low energies, such that quarks and gluons are only observable in form of hadron bound states such as the protons and neutrons or the pions. 

That the gluons are massless implies that if a gluon energy is very small or if it is collinear to another particle, it can become unresolved. This means that it is effectively invisible, yielding a strong connection with S-matrix elements without that gluon. This connection is associated with cancelling infrared divergent contributions in both types of matrix elements which become more intricate when the order in perturbation theory or the number of external gluons increases. Depending on the observable considered, these singular structures also imply the occurrence of large logarithmic corrections and are relevant in establishing proofs of factorization, where complicated scattering processes can be separated into universal (distribution) functions defined quantum field theoretically and themselves obeying a renormalization group flow. Well known and established examples are the parton distribution functions, describing the longitudinal momentum distribution of quarks and gluons in hadrons like the proton, or fragmentation functions, describing the momentum distribution of hadrons emerging from an inclusive hard interaction. This factorization and the field theoretic concepts on which factorization is based on are, in one way or another, the foundation of all theoretical predictions and simulations for collider processes where the strong interactions play any role.

Within the particle physics community, on the one side, there is continuous progress in improving the theoretical description within well-established factorization approaches, e.g. by adding higher order $\alpha_s$ corrections. On the other side, there is an endeavor to extend our systematic knowledge on factorization structures to somewhat less established processes and non-perturbative effects, where the understanding is more limited or subject to less rigorous modelling approaches, or to extend factorization beyond the leading power. The ESI thematic programme “New Paradigms for Harnessing Quantum Field Theory at Colliders” is intended to provide a development, communication and collaboration space for a number of such less established types of aspects, which are becoming increasingly attractive concerning novel theoretical insights and at the same time are becoming more important in experimental analyses. The focus topics of the thematic program, which are well interconnected, are outlined below. Progress on many of these theoretical directions will also have a direct impact on the ongoing experimental collider program and the analysis of the acquired data at the LHC.

The purpose of the workshop is to bring together internationally recognized experts and young researchers at the interface of QFT and collider physics phenomenology. We like to support exchange and collaboration of groups, working on connected directions but using different approaches, to foster new developments and insights into many interesting questions and to contribute towards new developments. 

Topics and Structure of the Workshop

The workshop lasts for 5 weeks and each week roughly focuses on one of five focus topics. The tentative schedule is as follows. 

July 27 - July 31: Week1 - QCD at Next-to-Leading Power: Factorization and Novel Singularities

The week focuses on the physics of effects that are formally suppressed from the perspective of established leading power factorization theorems.

August 3 - 7:  Week 2 - Energy-Energy Correlators for Collider QCD  

The week focuses on angular sensitive collider observables and inclusive fixed-particle correlation function weighted by the particle energy.

August 10 - 14: Week 3 - Color Evolution from Non-Global Logarithms to Small-x

The week focuses on improving the understanding of observables where certain parts of phase space are excluded.

August 17 - 21: Week 4 - Improving Perturbative Precision and the Treatment of Nonperturbative effects in Cross Sections and Simulations

The week focuses on new developments adding higher perturbative orders and precision in cross section predictions and simulations and the systematic understanding of nonperturbative effects in collider processes. 

August 24 - 28: Week 5- Transverse Momentum Distributions, from the LHC to the EIC

The week focuses on observables and factorization functions sensitive to momentum components perpendicular to the beam directions.