Towards accuracy at small x

UTC
Higgs Centre for Theoretical Physics (James Clerk Maxwell Building, King's Buildings, Edinburgh)

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
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Description

The aim of this meeting is to bring together experts in small-x physics to discuss recent progress in the field. Topics to be discussed include collider phenomenology, amplitudes and calculations with transverse-momentum-dependent distributions at higher orders. The workshop will feature some review talks on the following topics

• Theory Overview (Stefano Forte)
• Experimental Overview (Paul Newman)
• Scattering Amplitudes (Claude Duhr)
• Amplitudes in the Regge limit (Leonardo Vernazza)
• BFKL and impact factors at NLO (Giovanni Chirilli)
• Parton Distribution Functions and LHC phenomenology (Marco Bonvini)
• Calculations in kT-factorisation (Andreas van Hameren)
• Unintegrated Parton Densities (Francesco Hautmann)
• Coulomb gluons and factorization (Jeff Forshaw)
• Jets in the High Energy Limit (Jeppe Andersen)
• Jets in the BFKL formalims (Samuel Wallon)

Furthermore, we encourage the submission of abstracts for shorter talks on more specialised topics. In this context, abstracts from PhD students and postdocs working in this field are particularly welcomed.

Accommodation

Please follow this link to view available B&Bs and guesthouses close to the Kings Building Campus and the James Clerk Maxwell Building. Please inquire about academic rates. Further information on the venue can be found here .

Participants
• Andreas van Hameren
• Bertrand Ducloué
• Claude Duhr
• Edmond Iancu
• Emmet Byrne
• Francesco Hautmann
• Giovanni Antonio Chirilli
• Giulio Falcioni
• Graeme Nail
• Jeffrey Forshaw
• Jennifer Smillie
• Jeppe Andersen
• Leonardo Vernazza
• Lorenzo Magnea
• Maksim Nefedov
• Marco Bonvini
• Marian Heil
• Paul Newman
• Richard Ball
• Robin Marzucca
• Samuel Wallon
• Simone Marzani
• Stefano Forte
• Tommaso Giani
• Vittorio Del Duca
• Yair Mulian
• Zoltan Nagy
• Tuesday, 10 September
• 09:00 10:00
Theory Overview 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Prof. Stefano Forte (Università di Milano)
• 10:30 11:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 11:00 12:00
Experimental overview 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Prof. Paul Newman (University of Birmingham)
• 12:30 14:00
Lunch 1h 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 14:00 15:00
Parton Distribution Functions and LHC phenomenology 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Dr Marco Bonvini (INFN Roma 1)
• 15:30 16:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 16:00 16:20
Collinear resummations for the non-linear evolution in QCD at high-energy 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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 $x$.

Speaker: Edmond Iancu (Institut de Physique Theorique de Saclay)
• 16:30 16:50
Drell-Yan at small-x 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Tommaso Giani
• 17:00 17:20
Lipatov's EFT at one loop 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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

Speaker: Maxim Nefedov (II Institute for theoretical Physics, Uni. Hamburg; Samara National Research University)
• Wednesday, 11 September
• 09:00 10:00
Unintegrated Parton Densities 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Dr Hautmann Francesco (University of Oxford)
• 10:30 11:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 11:00 12:00
Calculations in kT-factorisation 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Dr van Hameren Andreas (Instytut Fizyki Jądrowej)
• 12:30 14:00
Lunch 1h 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 14:00 15:00
BFKL and impact factors at NLO 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Giovanni Antonio Chirilli (University of Regensburg)
• 15:30 16:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 16:00 16:20
Forward jet cross sections: from trijet to NLO dijet 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Yair Mulian (University of Jyväskylä)
• 16:30 16:50
Forward particle production in proton-nucleus collisions at next-to-leading order 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Bertrand Ducloue
• 17:00 17:20
Conformal invariance of TMD rapidity evolution 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Giovanni Antonio Chirilli (University of Regensburg)
• 19:00 21:00
Workshop Dinner 2h Surgeons Quarters

Surgeons Quarters

Nicolson Street, Edinburgh EH8 9DW
• Thursday, 12 September
• 09:00 10:00
Jets in the High Energy Limit 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Dr Jeppe Andersen (IPPP Durham University)
• 10:30 11:00
Break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 11:00 12:00
Jets in the BFKL approach 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Samuel Wallon (Paris Sud)
• 12:30 14:00
Lunch 1h 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 14:00 15:00
Scattering Amplitudes 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Claude Duhr (CERN and Université catholique de Louvain)
• 15:30 16:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 16:00 17:00
Amplitudes in the Regge limit 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Leonardo Vernazza (University of Edinburgh)
• 17:30 17:50
Scattering Amplitudes in the High-Energy Limit of N=4 SYM 20m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Robin Marzucca (UCLouvain)
• Friday, 13 September
• 09:00 10:00
Coulomb gluons and factorization 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
Speaker: Prof. Forshaw Jeffrey (University of Manchester)
• 10:30 11:00
Coffee break 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
• 11:00 12:00
Effect of Glauber (Coulomb) gluon in parton shower 1h Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD

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.

Speaker: Zoltan Nagy (DESY)
• 12:30 14:00
Lunch 1h 30m Higgs Centre for Theoretical Physics

Higgs Centre for Theoretical Physics

James Clerk Maxwell Building, King's Buildings, Edinburgh

Peter Guthrie Tait Road, Edinburgh, EH9 3FD
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