Research Francesco Hautmann

Abstract

An accurate, precise knowledge of PDFs is a key input of analyses at hadron colliders, and simultaneously a crucial output of the measurements made. The issue of accurately determining the PDFs, and their errors, is thus critical to the physics goals of the LHC. However, the current PDFs are faced with challenges on multiple fronts. Experimentally, the greater data accuracy ensures increasing issues of dataset tensions and correlations, meanwhile as the number, complexity and precision of datasets grows so does the methodological challenge of understanding apparent inconsistencies, limiting the reduction in PDF errors. In addition, the reduction of experimental uncertainties necessitates, for the first time, the inclusion of theoretical uncertainties in the PDFs – a significant challenge. Such challenges will increase over the coming years and may limit future LHC physics analyses unless action is taken. The over-arching research objective of my proposal is tackle these issues head-on, in order to develop the next generation of world-leading MSHT PDFs - MSHT2025, of greater accuracy and precision than ever before. I will then study the impact of the PDFs across a variety of key experimental channels for LHC physics. At the same time I will also combine our world-leading collinear PDFs, with the cutting edge transverse momentum dependent PDF approach at Antwerp, representing the production of TMDPDFs in a simultaneous global fit for the first time, a major step forward.

Researcher(s)

• Promoter: Van Mechelen Pierre
• Co-promoter: Hautmann Francesco
• Fellow: Cridge Thomas

Research team(s)

• Particle Physics Group

Project type(s)

• Research Project

Abstract

In this project, I want to address a crucial problem in modern particle physics, namely the quest for the proton's 3D structure. According to the well-established theory of Quantum Chromodynamics, this building block of all visible matter is a composite particle built from elementary partons: quarks and gluons. Many collider experiments can be successfully described in a simple one-dimensional picture where these partons move in the same direction as their parent proton. This picture fails, however, when experiments are sensitive to the internal motion or spin correlations of the partons, nor can it account for most of the proton's main properties such as its radius, mass, and spin. To answer such fundamental questions, the full 3D structure of the proton needs to be explored. This structure can be extracted from experiments and encoded into 'transverse momentum dependent parton distribution functions' (TMDs). In this project, I will apply the promising new 'Parton Branching' (PB) method to the study of spin polarized TMDs, which are still poorly known but are essential to solving the puzzles mentioned above. The PB approach was recently developed at the UAntwerp and in DESY, and proved already very successful in the description of unpolarized TMDs. This project is extremely timely since the study of TMDs is a driving force behind several proposed new experiments worldwide (in CERN, BNL, JLab,...), among which the recently approved Electron-Ion Collider (EIC).

Researcher(s)

• Promoter: Van Mechelen Pierre
• Co-promoter: Hautmann Francesco
• Fellow: Taels Pieter

Research team(s)

• Particle Physics Group

Project type(s)

• Research Project

Abstract

Precision measurements have a prominent position at the Large Hadron Collider (LHC) as well as in the new accelerators' physics program and they relay on accurate theoretical predictions. In this proposal, a new way of obtaining predictions, the Parton Branching (PB) method, is discussed. The method, based on transverse momentum dependent (TMD) factorization theorem, aims in applicability to exclusive collider observables in a wide kinematic range. The basic element of cross sections calculations are parton distribution functions (PDFs). In contrast to the widely used collinear approach, the PB does not neglect the 3-dimensional structure of proton: the TMD PDFs (TMDs) are determined thanks to exact kinematic calculation. In this project outline an extensive theory program is proposed to establish connection between the PB and other approaches and to push the PB accuracy from next-to-leading logarithmic approximation to next-to-next-to-leading. The possibility of including small x together with small qt resummation within one approach by using TMD splitting functions will be investigated. The outcome of the project will be a big step forward in a common understanding of the TMD factorization and resummation. The theory developments will result in the new TMDs fit procedure within xFitter package, improved by incorporating the Drell-Yan data. The new TMDs will be used to obtain precise predictions for the crucial DY precision measurements at Run III and High Luminosity LHC.

Researcher(s)

• Promoter: Van Mechelen Pierre
• Co-promoter: Hautmann Francesco
• Fellow: Lelek Aleksandra

Research team(s)

• Particle Physics Group

Project type(s)

• Research Project

Abstract

This research proposal focuses on the new kinematic region of highly energetic, nearly back-to-back jets which will be explored for the first time at the LHC Run II. Our approach is based on recognizing that in the back-to-back region theoretical predictions for jet distributions are sensitive, despite the large transverse momentum of each individual jet, to Quantum Chromodynamics (QCD) colorcorrelation effects which go beyond the expectation of customary next-to-leading-order or next-tonext- to-leading-order calculations, and lead to novel "color entanglement" processes. We will employ advanced QCD factorization and resummation techniques to investigate these effects theoretically, to identify relevant jet observables, and to interpret the results of measurements of multi-TeV, nearly back-to-back jets which we will perform with the CMS detector at Run II. Phenomenological and experimental studies will focus on the jet transverse momentum imbalance, on the azimuthal distance between the jets, and on the azimuthal correlation between the leading jet transverse momentum and the transverse momentum imbalance. The outcome of the proposed studies will be a high-impact set of methods to deal with QCD color correlations in multi-jet final states, which could be used both for precision physics, possibly revealing new aspects of the Standard Model, and for searches for physics beyond the Standard Model in multi-jets channels, both at the LHC and future high-luminosity experiments.

Researcher(s)

• Promoter: Van Mechelen Pierre
• Co-promoter: Hautmann Francesco
• Co-promoter: Van Haevermaet Hans
• Co-promoter: Van Remortel Nick

Research team(s)

• Particle Physics Group

Project type(s)

• Research Project