Seminars in Particle Physics Phenomenology at the Physics Department of Torino

Hadrons are strongly bound, yet their spectra can be classified as for atoms (and molecules). The apparent dominance of the valence (qq-bar, qqq) components of QCD bound states is paradoxical: The strong binding would be expected to generate an abundance of quark and gluon constituents. I recall the standard bound state methods of QED, and propose an equivalent, more intuitive approach. In QCD it allows to introduce the hadron scale through the fixing of temporal (A⁰ = 0) gauge, giving a confining potential which depends on a single parameter Λ. The features of the qq-bar bound states formed by this potential are promising even in the α_s → 0 limit.

Wednesday, 11th October 2023, 14:30 — Sala Wataghin

At the LHC, single top quarks are mainly produced through a t-channel W boson exchange, q+b→q′+t. QCD corrections to this process have been known for a while in the structure function approximation. However, at NNLO this approximation is no longer exact and so-called non-factorisable corrections also contribute. Although these corrections are colour-suppressed, there is reason to expect that they may provide a non-negligible impact. In this talk I will present the calculation of the non-factorisable contribution and discuss their phenomenological impact on single-top production at the LHC and FCC.

*Wednesday, 8th February 2023, 14:30 — Sala Wataghin *

Multi-jet rates at hadron colliders provide a unique possibility for probing Quantum Chromodynamics (QCD), the theory of strong interactions. By comparing theory predictions with collider data, one can directly test perturbative QCD, extract fundamental parameters like the strong coupling and search for physics beyond the Standard Model. Recent developments enabled lifting three-jet cross-sections to next-to-next-to-leading order (NNLO) in QCD. I will present numerical results for three-to-two jet ratios and event shapes at the Large Hadron Collider (LHC). Then, I will discuss the first extraction of the strong coupling constant from event shapes at the LHC with NNLO QCD accuracy.

Wednesday, 22nd February 2023, 14:30 — Aula Verde

The success of experiments in High Energy Physics relies on the accuracy of Monte Carlo (MC) predictions. The field of MC generators is now in a phase of active development before the start of new experiments and machines for which the highest precision is a demand. The commonly used MC generators are based on collinear factorization which assumes the partons are collinear with the hadron they are constituents of. For some classes of observables, with more than one relevant energy scale, this assumption is not enough and the transverse degrees of freedom must be considered. This can be achieved in a theoretical framework of Transverse Momentum Dependent (TMD) factorization. The study of the 3D structure of hadrons is also one of the main points in the agendas of newly planned accelerators. In my talk, I present the TMD Parton Branching (PB) method: an MC approach to obtain high-energy QCD predictions based on ideas originating from the TMD factorization. I explain the main concepts behind the parton branching algorithm implemented within the TMD PB method and discuss some aspects of the TMD evolution in this approach. I make connections with standard collinear and TMD approaches for parton evolution and present some of the PB applications to the LHC as well as lower energy experiments.

Wednesday, 8th March 2023, 14:30 — Sala Wataghin

I will present recent results on the computation of higher-order perturbative corrections to helicity amplitudes in Quantum Chromodynamics for scattering processes involving a massive boson and three partons, at next-to-next-to-next-to-leading-order (N3LO) of precision.

Wednesday, 8th November 2023, 14:30 — Sala Wataghin

Intersection theory allows to exploit the vector space structure obeyed by Feynman integrals, turning the decomposition to master integrals into the calculation of the projection of a vector into a basis, via scalar products called intersection numbers. In this talk I will discuss how the calculation of intersection numbers can be achieved via a purely rational algorithm, through the systematic use of polynomial series expansions, and its implementation over the finite fields using the FiniteFlow program.

Wednesday, 22nd March 2023, 14:30 — Sala Wataghin

The study of ttH production is crucial since it can provide a direct measure of the top Yukawa coupling. I will provide an overview of the experimental and theoretical state-of-the-art results concerning this interesting process. Moreover, I will illustrate how the ttH cross section can be computed at high transverse momentum exploiting the fragmentation function formalism. This approach simplifies the cross-section computation and it enables the resummation of large logarithms, an important feature in view of future colliders. In order to perform this calculation, the fragmentation functions for the production of a Higgs boson at NLO QCD were computed using modern higher-order perturbative computations techniques. I will illustrate the step needed to perform this computation from the field theoretic definition of the fragmentation to the details of the computation of the loop integrals.

Wednesday, 5th April 2023, 14:30 — Sala Wataghin

Accessing the polarisation state of weak represents a crucial step to improve our understanding of the electroweak-symmetry-breaking mechanism that is realised in nature. The recent ATLAS and CMS results have started triggering multiple efforts in the theory community, comprising the precise and accurate calculation of polarised-boson signals, as well as a number of novel approaches that enhance the sensitivity to polarisation. I will focus the talk on two main topics: the recently achieved NLOPS matching for polarised-boson pair production, and a neural-network strategy for the tagging of longitudinally polarised bosons at the LHC.

Wednesday, 12th December 2023, 16:00 — Sala Fubini

TBA

Wednesday, 22nd November 2023, 14:30 — Sala Fubini

The determination of Parton Distribution Functions (PDFs) is an example of inverse problem: a model is sought knowing a finite set of experimental observations. Given the fact that the model is a continuous function, i.e. an element of an infinite dimensional space, its determination from a discrete set of data is notoriously a ill-posed problem. In the currently used methodologies for PDF determination, the model is parameterized in terms of a finite (albeit large) set of parameters, which are then fitted to the observed data. This procedure, known as parametric regression, reduces the problem to a finite dimensional and solvable one, but generally it has the drawback of introducing some bias. A Bayesian approach provides a suitable alternative to address inverse problems, avoiding the need to introduce a finite-dimensional parameterization and recasting the problem in a probabilistic language. I will discuss a Bayesian methodology for the determination of PDFs, providing examples for the determination of PDFs from Deep Inelastic Scattering data and from lattice matrix elements.

Wednesday, 6th December 2023, 14:30 — Sala Wataghin