Data di Pubblicazione:
2020
Citazione:
SUBSTRUCTURE AT COLLIDERS / G. Stagnitto ; tutor: F. Stefano, M. Cacciari (Université de Paris), G. Soyez (IPhT Saclay); coordinatore Scuola di Dottorato: M. Paris. Dipartimento di Fisica Aldo Pontremoli, 2020 Sep 14. 33. ciclo, Anno Accademico 2020. [10.13130/stagnitto-giovanni_phd2020].
Abstract:
In this PhD thesis we investigate several aspects of parton distribution functions (PDFs) and
jets as applicable to the physics underpinning the Large Hadron Collider (LHC) as well as future
colliders. We first discuss jet observables at the LHC, focusing on the single-jet inclusive cross
section. We introduce possible alternative definitions, which weigh the individual contributions
coming from each jet in the event and are thus unitary by construction. We also clarify the
origin of some problematic aspects of the standard definition. Secondly, within the hadronic
PDF fitting framework of the NNPDF collaboration, we investigate the inclusion of single-jet
inclusive and dijet measurements into a global PDF fit, using QCD next-to-next-to-leading order
predictions for jet processes. We field-test which observables lead to better perturbative stability,
better PDF compatibility with other data, better fit quality, and more stringent constraints on
the PDFs. Thirdly, we focus on an analytical understanding of machine learning techniques used
for quark versus gluon discrimination, a hot topic in jet substructure studies. We construct a
new version of the widely used N -subjettiness variable, which features a simpler theoretical
behaviour than the original one, while maintaining, if not exceeding, the discriminating power.
We input these new observables to the simplest possible neural network, with only one neuron,
and we study analytically the network behaviour at leading logarithmic accuracy. We also
compare our analytic findings to a more realistic neural network trained with Monte Carlo
pseudo-data. Fourthly, we compute the unpolarised electron, positron, and photon PDFs at next-
to-leading logarithmic accuracy in QED, which are crucial for high-precision predictions needed
for future e + e − colliders. We present both numerical and analytical results. The analytical
predictions, defined by means of a specific additive formula, provide a large-z analytical solution
that includes all orders in the QED coupling constant α, with a small- and intermediate-z
solution that includes terms up to O(α 3 ). The content of this thesis is based on arXiv:1906.11850,
arXiv:1911.12040, arXiv:2005.11327, and arXiv:2007.04319.
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
G. Stagnitto
Link alla scheda completa: