Parton Showers and Resummation 2024

2 Jul 2024, 09:00 → 5 Jul 2024, 23:30 Europe/Zurich

HS 05.12 (Universität Graz)

The aim of the PSR workshop is to bring together the QCD communities involved in analytic resummations and parton shower event generators. The 2024 PSR workshop will focus on new developments both in analytic resummation and parton shower algorithms, as well as the relation between them.

Overview talks include contributions by:

• Andrea Banfi
• Silvia Ferrario Ravasio
• Roman Kogler
• Matthias Neubert

 

Registration deadline: Registrations and submissions of abstracts will be accepted until May 18th, 2024. Please indicate in the abstract submission if you intend to talk at PSR or the satellite meeting using the "Track" menu in the form. The meeting will take place in person, we do not plan any remote talks.

The core workshop will start on July 2nd, 2024 in the morning and will run until July 4th, late afternoon, with ample time for discussion. It will then be followed by a one-day satellite meeting on hadronization models and hadronization corrections, both in analytic approaches as well as in Monte Carlo event generators. The workshop is jointly organized by Jeff Forshaw, Axel Maas, Simon Plätzer (chair) and Malin Sjödahl.

July 2nd - 4th, 2024: Core Workshop

July 5th, 2024: Satellite Meeting on Hadronization Models and Hadronization Corrections

 

After registration, payment instructions will be sent to you by email. The conference fee is EUR 140 for the main Parton Shower Resummation workshop, and an additional EUR 20 for the satellite meeting on hadronization. The conference fee includes the venue, coffee breaks, and the workshop dinner. Payments will need to be done by credit card and arrive before May 18th, 2024 latest. We will only consider refunding of fees in very exceptional cases after requests in writing have been directed to the conference organizers. Strictly no refunding is possible after May 18th, 2024.

Tuesday, 2 July

09:30 → 09:40 Introduction and welcome by the organizers

slides.pdf

09:40 → 10:20 Parton Showers

Speaker: Silvia Ferrario Ravasio (CERN)

2024_07_02_PSR.pdf

10:30 → 11:00 Coffee

11:00 → 12:30 Topical talks 1

11:00 Towards a NLO Parton Shower: Gauge Choice

We explore the features of interpolating gauge for QCD. This gauge, defined by Doust and by Baulieu and Zwanziger, interpolates between Feynman gauge or Lorenz gauge and Coulomb gauge. We argue that it could be useful for defining the splitting functions for a parton shower beyond order $\alpha_s$ or for defining the infrared subtraction terms for higher order perturbative calculations.

Speaker: Zoltan Nagy

znagy-graz.pdf

11:30 Implementing Dipole Showers with Global Recoil in Herwig 7

Implementing NLL-accurate dipole showers is an active area of research today. In this talk, I will present updates on implementing the Forshaw-Holguin-Plätzer dipole shower model in Herwig. I will summarise the mechanisms for the global conservation of recoil components with NLL accuracy at LEP. I will also present parton-level results for jet rates and event shape observables and combine these with the complete Herwig workflow to show preliminary results from the event generator.

Speaker: Siddharth Sule (University of Manchester (GB))

FHP-Mapping.nb

s-sule-dsgr-psr24.pdf

12:00 Multi-emission kernels for parton showers

Speaker: Maximilian Loeschner

Loeschner-PSR-Graz-2024.pdf

12:30 → 14:00 Lunch

14:00 → 15:30 Topical talks 2

14:00 Electroweak Sudakov Logarithms

Speaker: Axel Torsten Maas

psr24.pdf

14:30 N3LL resummation of one-jettiness for Z-boson plus jet production at the LHC

In this talk I will present the resummation of one-jettiness up to N3LL accuracy for the Z+jet production process at the LHC. The resummed calculation is matched to the corresponding fixed-order predictions extending the validity of the results to regions of the phase space where further hard emissions are present. I will show numerical results and discuss the convergence of the different resummation orders.

Speaker: Alessandro Broggio (University of Vienna)

Broggio_PSR24_Graz.pdf

15:00 NNLL collinear fragmentation and Parton showers

Over recent years the logarithmic accuracy of parton showers has been advancing rapidly, first to NLL and more recently towards NNLL. In this talk I will focus on one aspect of the push towards NNLL accuracy, the triple collinear limit. I will present work towards the inclusion of real triple collinear and corresponding one loop corrections to one-to-two splittings in a parton shower algorithm. I will also discus NSL resummed results sensitive to this limit, which are relevant to NNLL parton showers.

Speaker: Jack Helliwell (University of Oxford (GB))

NNLL_collinear_fragmentation.pdf

15:30 → 16:00 Coffee

16:00 → 17:00 Topical talks 3

16:00 Resummation or exclusive exponentiation

The principles of exclusive exponentiation, which enables resummation of dominant parts of amplitudes to all orders, and which enable use of fixed order amplitudes , still preserving full and exact multiphoton phase space generation, are explained.
The solutions based on conformal symmetry as used in kkmc Monte Carlo, as well as solution based on KLN theorem as used in Photos Monte Carlo, will be addressed.
Challenges for implementation of third order matrix elements in such schemes will pointed into.

Speaker: Zbigniew Andrzej Was (Polish Academy of Sciences (PL))

was.pdf

16:30 High precision tests of perturbative QCD without renormalization scale and scheme ambiguities.

We discuss and show our recent developments and applications of the PMC method to important physical processes. Results are also compared with those obtained with other methods.
The renormalization scale setting in QCD is a crucial problem for high precision tests of the Standard Model (SM). The conventional practice of setting the renormalization scale to the typical scale of a process Q, namely to the momentum transfer and to determine theoretical errors by varying it in a range of two, is affected by "renormalization scale and scheme ambiguities" that lead to large errors in the theoretical predictions. The Principle of Maximum Conformality (PMC) provides a systematic way to remove such ambiguities from perturbative calculations satisfying at once the renormalization group invariance and the self-consistency conditions deriving from the renormalization group.

Speaker: Dr Leonardo Di Giustino (Insubria University and INFN-Bicocca Milano)

LDG-talk-PSR24.pdf

Wednesday, 3 July

09:00 → 09:45 SCET and the Glauber Series

Speaker: Matthias Neubert (Johannes Gutenberg Universitat Mainz)

Neubert_PSR2024.pdf

09:45 → 10:30 QCD Resummation

Speaker: Prof. Andrea Banfi (University of Sussex)

banfi_PSR24.pdf

10:30 → 11:00 Coffee

11:00 → 12:30 Topical talks 4

11:00 Colour Evolution and Infrared Physics

Speaker: Simon Platzer (University of Graz (AT))

plaetzer.pdf

11:30 Developing an amplitude level parton shower (CVolver)

We will overview the progress made towards building an amplitude level parton shower evolution algorithm. We will cover the advantages of this approach and the results generated so far.

Speaker: Fernando Torre González (The University of Manchester)

PSR24 CVolver-1.pdf

12:00 Resummation of non-global observables at subleading accuracy

An intricate pattern of enhanced higher-order corrections known as non-global logarithms arises in cross sections with angular cuts. While the leading logarithmic terms have been calculated numerically two decades ago, the resummation of subleading non-global logarithms remained an open problem. In this talk, I will explain how the next-to-leading non-global logarithms can be resummed using renormalisation group methods in effective field theory.

Speaker: Nicolas François Schalch

psr_2024.pdf

12:30 → 14:00 Lunch

14:00 → 15:30 Topical talks 5

14:00 Heavy flavour jet substructure for heavy ion collisions

In this talk, we will present a theoretical framework for studying heavy flavor jet substructure for dense QGP medium based on the factorised picture between vacuum-like and medium-induced radiations, based on arXiv:2312.15560 and ongoing works. We studied the $z_g$ distribution for heavy flavor, i.e. bottom and charm quark, jets propagating through the dense QCD medium. However, unlike the previous study in the BDMPS-Z framework, which takes $\omega\ll\omega_{c}$ limit, and leads to a simplified and factorised formula for the spectrum, we use the full expression. In the end, the expanding medium extension and some preliminary results will be introduced briefly.

Speaker: Chang Wu (Technion - Israel Institute of Technology)

PSR24-Chang.pdf

14:30 Heavy flavour jet substructure

In this talk I will present our research activity on jets substructure with heavy flavour. Our primary goal is to obtain a more profound understanding of these objects. To this end, we employ resumed perturbation theory tailored specifically for jets initiated by heavy quarks. Furthermore, we will present analytical calculations targeting various observables that characterise jets, including angularities, energy correlation functions and Soft Drop variables. I will display the main differences between our findings and the massless computations. Finally, I will compare our analytical results with Monte Carlo simulations.

Speaker: Andrea Ghira (Università degli studi di Genova)

Graz_AG.pdf

15:00 Exploring near-conformal Hidden Valley parton showers

Dark-showers offer a compelling collider signature for Hidden Valley models featuring a confining dark sector. Our work extends the investigation of these models to near-conformal theories where the running coupling, controlled by renormalization group equations (RGE), flows near to an infra-red fixed point. We establish a framework of two classes of RGE solutions which cover much of the parameter space of confining theories, allowing us to present the first results of such near-conformal dark sector parton showers.

Speaker: Joshua Lockyer

Lockyer_PSR_final.pdf

15:30 → 16:00 Coffee

16:00 → 18:00 Discussion and guided city tour

19:00 → 22:00 Conference dinner

Thursday, 4 July

09:00 → 10:30 Topical talks 7

09:00 Parton Showers on GPU with GAPS

Modern GPUs can concurrently execute threads and manage diverging tasks, enabling developers to write more sophisticated algorithms than ever before. In this talk, I will present a parallelised Sudakov veto algorithm capable of generating emissions simultaneously for multiple events. I will also showcase the GPU parton shower GAPS, validating the physics with LEP observables and comparing the execution times with a near-identical CPU-only parton shower.

Speaker: Siddharth Sule (University of Manchester (GB))

s-sule-gaps-psr-24.pdf

09:30 The NNLO soft function for N-jettiness in hadronic collisions

In this talk I'll present our recent work calculating the N-jettiness soft function, based on an extension of the SoftSERVE framework to the general case of N+2 jets and beams for a priori general global observables. I will comment on our approach, present an explicit grid scanning the 2-jettiness soft function, and shed some light on the behaviour of the N-jettiness soft function at the edges of phase space, when two jets/beams become collinear.

Speaker: Rudi Rahn (University of Vienna)

PSR24_Rahn.pdf

10:00 Multiplet Bases

The treatment of QCD color structure at high energy colliders is typically based on non-orthogonal and overcomplete trace- or color-flow "bases". In principle has been known for a while how to construct orthogonal multiplet bases, based on representation theory. While these bases avoid the prohibitive factorial square scaling when squaring the color structures, they suffer from the same bad scaling once, during construction. On the other hand, multiplet bases allow for straight-forward color treatment using using Wigner 6j (and 3j) coefficient. In this talk I will review strategies for color structure treatment, illustrate how to calculate with Wigner 6j coefficients, and further argue that we can calculate those coefficients without ever constructing the corresponding bases. This opens up for a very efficient treatment of color-summed QCD color structure.

Speaker: Malin Sjödahl

MalinSjodahlPSR24.pdf

10:30 → 11:00 Coffee

11:00 → 12:30 Topical talks 8

11:00 Dark showers and hadronisation in Herwig

Most dark matter searches at the LHC focus on models where dark matter is a single stable particle, leading to traditional "MET+X" type searches. However recent years have shown a growing interest in "dark sector" which have a more complex internal structure. One such model is "dark showers", in which the particles in the dark sector interact with each other via a strong force similar to QCD in the Standard Model, which leads to the formation of "dark hadrons", some of which are stable DM candidates, and others of which decay to SM particles. This can give rise to unconventional experimental signatures, such as semi-visible and emerging jets.

Accurately simulating these dark showers is challenging since the hadronisation step is non-perturbative, and described by semi-empirical models, which require tuning to Standard Model data. However so far no extensive studies have been performed to determine the impact of hadronisation uncertainties on these types of models. In this talk I will describe the implementation of this dark shower model into the Herwig 7 Monte Carlo generator, introduce some novel jet substructure variables which can be used to distinguish dark showers from Standard Model QCD, and show the impact of varying the hadronisation parameters on these distributions.

Speaker: Dominic William Stafford (Deutsches Elektronen-Synchrotron (DE))

darkshowers_PSR_2024.pdf

11:30 Modified Cluster Dynamics

Speaker: Stefan Kiebacher

Presentation_Stefan_Kiebacher_PSR24.pdf

12:00 PDFs and TMDs from functional methods

Speakers: Eduardo Ferreira, Gernot Eichmann

ferreira_PSR24.pdf

12:30 → 14:00 Lunch

14:00 → 15:00 Topical talks 9

14:00 The Lund Jet Plane for boosted top quarks

We present a study of the density of emissions in the Lund Jet Plane for hadronic decays of boosted top quarks. We consider the case where all top quark decay products are reconstructed in a single large jet. The three-prong decay of the top quark offers a rich substructure where the two quarks from the W decay are not color-connected to the b quark, and all three quarks originate from the decay of a heavy resonance. We study the radiation pattern between these quarks and show the first attempt to disentangle effects from the parton shower and the hadronisation process.

Speaker: Mikel Mendizabal Morentin

Mikel-PSR2024.pdf

14:30 A blueprint for understanding the Monte-Carlo top quark mass parameter

To control the scheme of the Monte-Carlo (MC) top quark mass parameter several ingredients are mandatory, concerning the knowledge of the IR dynamics of the top mass sensitive observable, the MC parton shower and the MC hadronization evolution. I discuss these ingredients and their interplay for the simple case of 2-jettiness for boosted top production in electron-positron annihilation, where these ingredients are all known for the Herwig MC. Apart from having an at least NLL precise parton shower, which Herwig can provide for event-shapes, a crucial novel development is a QCD factorization compatible hadronization model, which I describe in some detail, and which yields hadronization corrections with a scheme-dependence controllable to NLO. The outcome is that for 2-jettiness the Herwig top mass mass parameter now represents a well defined and shower cut dependent renormalization scheme that can be quantified and controlled at NLO prediction. The approach I discuss represents a blueprint for controlling the scheme of the MC top mass parameter that may eventually be also applied to direct-type top quark mass measurements.

Speaker: Andre Hoang

Hoang-MCtopmass.pdf

15:00 → 15:30 Discussion

15:30 → 16:00 Coffee

16:00 → 16:30 Summary and outlook

Friday, 5 July

09:00 → 10:30 Talks and discussion

banfi-ares.pdf

10:30 → 11:00 Coffee

11:00 → 12:30 Talks and discussion

12:30 → 14:00 Lunch

14:00 → 15:30 Talks and discussion

15:30 → 16:00 Coffee

16:00 → 16:30 Summary and infomal discussions