Strategies to tackle the Quest for Hadronization

Project Information

SQuHadron

Grant agreement ID: 795475

DOI

10.3030/795475

Project terminated on 30 June 2022

EC signature date 17 April 2018

Start date 1 September 2019

End date 31 August 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 262 269,00

EU contribution

€ 262 269,00

Coordinated by

UNIVERSITA DEGLI STUDI DI PAVIA
Italy

Periodic Reporting for period 2 - SQuHadron (Strategies to tackle the Quest for Hadronization)

Reporting period: 2021-09-01 to 2022-08-31

Summary of the context and overall objectives of the project

Hadrons are the bound states of the strong nuclear force. They can be thought of as the smallest complex systems in nature.
The internal structure of hadrons in terms of their elementary constituents (partons) and the transformation of a parton into hadrons (hadronization) are two sides of the same coin, namely the nonperturbative core of Quantum Chromodynamics (QCD), the field theory describing the strong force.
Hadronization is a process intimately related to questions among the most important ones in physics: e.g. how do particles acquire their mass? What is the mechanism behind the confinement of the strong force?
The project “Strategies to tackle the Quest for Hadronization” (SQuHadron) pioneers new ways to extend our understanding of hadronization.

Factorization theorems allow us to describe hadronization in terms of fragmentation functions (FFs), which reflect the probability that a quark transforms into one or more hadrons.
A deeper understanding of hadronization requires the extension of the standard one-dimensional unpolarized FFs to multi-dimensional objects, including polarization and (non)perturbative contributions: the project will make significant steps forward in this direction.

The goals of SQuHadron are: complete the formalism for analyzing 3D unpolarized FFs and extract them from data; define a framework to study chiral-odd FFs for single-hadron, di-hadron and jet production.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project SQuHadron deals with generalization of standard fragmentation functions, which have already and widely been used as tools to access the internal structure of the hadrons.
Their generalization will turn them into much more sophisticated “probes”, whose phenomenological potential is very timely in the light of the current and future experimental efforts.

The benchmark reactions addressed in the project are electron-positron annihilation and semi-inclusive deep-inelastic scattering. According to the final states, different aspects of hadronization will be studied.

During the implementation of the whole action, specific contributions have been made to:
- the connection between the dynamical properties of quark propagation and hadronization
- the impact of dynamical mass effects on semi-inclusive scattering processes (e.g. how the dynamical mass of a quark affects reactions governed by the strong force)
- the improvement of the theoretical formalism to study processes sensitive to the transverse momentum of quarks and gluons
- the determination of fragmentation functions by using fits to experimental data
- assessing the impact of future experiments on the current knowledge of hadron structure and hadronization

The technical results have been presented in several workshops and conferences, both at the national and international level.
The goals of the action have been disseminated also through outreach events, both in person and via social media (e.g. broadcasted via Youtube).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project is expected to make significant progress in the field of hadronization, by refining the currently rather poor knowledge of certain classes of fragmentation functions (e.g. the multidimensional ones and the polarized ones).
These studies will pave the way to the exploration of new effects governed by the strong force and will have a significant impact also on the related studied of hadron structure.

The project involves fundamental science. Its most valuable societal outcome is knowledge and awareness. Nonetheless, the technologies developed to experimentally study these effects will have broad and long-lasting implications for society and its welfare.

Diagrams for the production of hadrons and jets in electron-positron annihilation.