Theory Overview

• Stefano Forte (Università di Milano)

Room: Higgs Centre for Theoretical Physics

Experimental overview

• Paul Newman (University of Birmingham)

Room: Higgs Centre for Theoretical Physics

Parton Distribution Functions and LHC phenomenology

• Marco Bonvini (INFN Roma 1)

Room: Higgs Centre for Theoretical Physics

Collinear resummations for the non-linear evolution in QCD at high-energy

• Edmond Iancu (Institut de Physique Theorique de Saclay)

Room: Higgs Centre for Theoretical Physics The next-to-leading order (NLO) Balitsky-Kovchegov (BK) equation describing the high-energy evolution of the scattering between a dilute projectile and a dense target suffers from instabilities unless it is supplemented by a proper resummation of the radiative corrections enhanced by large transverse logarithms. These instabilities are associated with large, anti-collinear, double logarithms which occur when the NLO corrections are computed from the evolution of the dilute projectile. We explain how to rewrite the NLO evolution in terms of the rapidity of the dense target. This avoids the large anti-collinear contributions but introduces new, collinear, instabilities, which are however milder since disfavoured by the typical BK evolution. We propose several prescriptions for resumming these new double logarithms and find only little scheme dependence. The resummed equations are non-local in rapidity and can be extended to full NLO accuracy. We present the first applications of these resummed equations to deep inelastic scattering at small Bjorken $x$.

Drell-Yan at small-x

• Tommaso Giani

Room: Higgs Centre for Theoretical Physics We study the formalism to resum differential distributions at small-x in the case of the DY process, extending results previously obtained for Higgs production in gluon fusion. We focus on rapidity and transverse momentum distributions, presenting results for both single and double differential cases. We implement our results in Hell, providing the resummed DY coefficient functions to be used in a global fit.

Lipatov's EFT at one loop

• Maxim Nefedov (II Institute for theoretical Physics, Uni. Hamburg; Samara National Research University)

Room: Higgs Centre for Theoretical Physics The techniques of loop calculations in Lipatov's gauge-invariant EFT for Multi-Regge Processes in QCD will be reviewed. The main challenges are rapidity divergences in loop integrals and calculation of integrals with several scales of virtuality. The talk is based on the results of: https://arxiv.org/abs/1905.01105 https://arxiv.org/abs/1902.11030

Unintegrated Parton Densities

• Hautmann Francesco (University of Oxford)

Room: Higgs Centre for Theoretical Physics

Calculations in kT-factorisation

• van Hameren Andreas (Instytut Fizyki Jądrowej)

Room: Higgs Centre for Theoretical Physics

BFKL and impact factors at NLO

• Giovanni Antonio Chirilli (University of Regensburg)

Room: Higgs Centre for Theoretical Physics

Forward jet cross sections: from trijet to NLO dijet

• Yair Mulian (University of Jyväskylä)

Room: Higgs Centre for Theoretical Physics Using the formalism of the light-cone wave function in pQCD together with the hybrid factorization, we compute the cross-section for two and three particle production at forward rapidities in proton-nucleus collisions. We focus on the quark channel, in which the three produced partons -- a quark accompanied by a gluon pair, or two quarks plus one antiquark -- are all generated via two successive splittings starting with a quark that was originally collinear with the proton. The produced partons are put on-shell by their scattering off the nuclear target, described as a Lorentz-contracted "shockwave". By using the three-parton component of the quark light-cone wave function, together with the virtual corrections, we can then present our progress on the computation of the next-to-leading order correction to the cross-section for the production of a pair of jets.

Forward particle production in proton-nucleus collisions at next-to-leading order

• Bertrand Ducloue

Room: Higgs Centre for Theoretical Physics Reaching next-to-leading order accuracy in perturbative calculations of particle production in QCD at high energy is essential for reliable phenomenological applications. In recent years, the Color Glass Condensate effective theory (the natural framework for such calculations) has indeed been promoted to NLO accuracy. However, the first NLO calculation of single-inclusive hadron production met with an unexpected difficulty: the cross-section suddenly turns negative at transverse momenta of the order of a few GeV, in a range where perturbation theory is expected to be reliable. We summarize recent efforts to understand and solve this issue, as well as to develop a running coupling scheme that can be used to consistently describe various processes in this formalism.

Conformal invariance of TMD rapidity evolution

• Giovanni Antonio Chirilli (University of Regensburg)

Room: Higgs Centre for Theoretical Physics The most known scheme to regulate the rapidity/UV divergences of the Transverse Momentum Distribution operators due to the infinite light-like gauge links is the Collis Soper Sterman formalism or the Soft Collinear Effective Theory formalism. An alternative choice is provided by the scheme used in the small-x physics. The corresponding evolution equations differ already at leading order. In view of the future Electron-Ion Collider accelerator, which will probe the TMDs at values of the Bjorken x in the region between small-x to x $\sim$ 1, the different formalisms need to be reconciled. I will discuss the conformal properties of TMD operators and present the result of the conformal rapidity evolution of TMD operators in the Sudakov region.

Jets in the High Energy Limit

• Jeppe Andersen (IPPP Durham University)

Room: Higgs Centre for Theoretical Physics

Jets in the BFKL approach

• Samuel Wallon (Paris Sud)

Room: Higgs Centre for Theoretical Physics

Scattering Amplitudes

• Claude Duhr (CERN and Université catholique de Louvain)

Room: Higgs Centre for Theoretical Physics

Amplitudes in the Regge limit

• Leonardo Vernazza (University of Edinburgh)

Room: Higgs Centre for Theoretical Physics

Scattering Amplitudes in the High-Energy Limit of N=4 SYM

• Robin Marzucca (UCLouvain)

Room: Higgs Centre for Theoretical Physics We have developed a new, efficient mathematical framework to perform computations of scattering amplitudes in the multi-Regge limit of N=4 SYM. Using this framework we were able to compute scattering amplitudes to very high perturbative orders as well as high multiplicities. We can further use this formalism to prove the factorization of MHV scattering amplitudes in MRK to all loop orders into a finite number of building blocks in momentum space as well as completely define the function space of scattering amplitudes in the multi-Regge limit of N=4 SYM.

Coulomb gluons and factorization

• Forshaw Jeffrey (University of Manchester)

Room: Higgs Centre for Theoretical Physics

Effect of Glauber (Coulomb) gluon in parton shower

• Zoltan Nagy (DESY)

Room: Higgs Centre for Theoretical Physics In the first half of this talk I would like to discuss briefly the structure of the parton shower cross sections focusing on the effect of the Glauber gluons. In the second part I will discuss the implementation of the colour evolution in parton shower and show some results for rapidity gap survival probability.