Dienstag, 11.07.2023, 16:30 Uhr
Ilaria Brivio (University of Bologna, Italy)
Host: Johannes Erdmann
Dienstag, 04.07.2023, 16:30 Uhr
Colomba Brancaccio / Lukas Simon (RTG / RWTH Aachen University)
Student presentations B
Dienstag, 20.06.2023, 16:30 Uhr
Danilo Meuser / Jonanathan Hermann (RTG / RWTH Aachen University)
Student presentation A
Dienstag, 06.06.2023, 16:30 Uhr
Terry Generet (RTG, RWTH Aachen University)
Top-pair production in association with a B-hadron at NNLO
In this talk, I will present NNLO QCD predictions for several differential distributions of B-hadrons in top-pair events at the LHC. After discussing the first calculation of this kind, I will describe several improvements that have been made recently. First of all, a new set of B-hadron fragmentation functions has been obtained, which features reduced uncertainties. Additionally, the decay of the produced B-hadron to a muon or a J/ψ meson has been incorporated, allowing us to make predictions for distributions involving those decay products, which is what is typically measured by experiments. These improvements are then applied to a second calculation, which studies the effect of the NNLO corrections on several methods of measuring the top-quark mass.
Host: Felix Eschment
Dienstag, 23.05.2023, 16:30 Uhr Zoom
Abideh Jafari (DESY and Isfahan University of Technology
Still on top after about three decades
The top quark continues to be appealing to high energy physicists even though its discovery was 30 years ago. The heaviest known particle has still a number of aspects to scrutinize, while it might be “the portal” to new theories that address the shortcomings of the standard model (SM) of particle physics. The wealth of LHC data at the highest-ever-reached energies provides a handful of events where top quarks are produced with multiple other heavy (or light) particles. We are in an era where, for the first time, top quark interactions can be measured directly and without strong assumptions on the underlying theory. I will go through a number of measurements targeting top quark electroweak interactions, and discuss how we are putting different pieces together towards a more complete picture of the SM top sector. Alongside this effort, I will point out other corners of the SM where different new phenomena might be routed in the same theory, going beyond what we know.
Host: Kerstin Borras
Dienstag, 25.04.2023, 16:30 Uhr
Markus Steidl (KIT, Karlsruhe)
KATRIN experiment - What is the absolute mass scale of neutrinos?
The neutrino mass remains unfinished business for the standard model as not only the mass generating mechanism is unknown but even the mass scale. Different methods are currently applied in experiments to reveal this experimental challenge. In this talk the method of measuring the neutrino mass via spectroscopy of the beta electrons from the tritium decay with the KARlsruhe TRitium Neutrino experiment (KATRIN) is explained and latest results presented. At the end of the talk we look a few years ahead and get an idea how KATRIN will adapt its configuration to be also sensitive to sterile keV neutrinos.
Host: Robert Harlander
Dienstag, 18.04.2023, 16:30 Uhr
Rene Poncelet (Cambridge University, UK)
Jet identification and flavoured jet algorithms
The study of jets is a staple of the research program at the LHC. As suitably defined sets of highly-energetic particles, they constitute a valuable tool to establish a link between Quantum Chromodynamics (QCD) of quarks and gluons and the realm of actual strongly-interacting particles, baryons and mesons. Besides the general importance of jets for collider phenomenology, there is a growing interest in studying jet substructure to disentangle various QCD effects governing jet dynamics. Specifically, "flavoured" jets allow access to the partonic structure of the hard scattering event, which in turn can be used for Standard Model measurements, Parton Distribution Function fits, New Physics searches and tuning/improvement of Monte Carlo simulations. In this talk, I discuss the challenges in defining flavoured jet cross sections in theory and experiment and the implications for phenomenology.
Host: Malgorzata Worek
Dienstag, 11.04.2023, 16:30 Uhr
Rikkert Frederix (Lund University, Sweden)
Matching and Merging: Combining Matrix Elements and Parton Showers
The presentation will focus on the FxFx merging technique, which has become a popular method for simulating multi-jet final states in particle physics. The merging of matrix-element calculations at different jet multiplicities is a crucial step in the prediction of the event rates for high-energy collisions. In the FxFx merging technique, matrix-element calculations for fixed numbers of jets are combined using a set of merging scales to obtain a smooth and accurate description of the full jet multiplicity spectrum. We will provide an accessible overview of the theoretical basis of this technique and its practical implementation in the event generator MadGraph5_aMC@NLO. Additionally, we will showcase some recent work on improving this method in the context of "electroweak jets”.
Host: Malgorzata Worek
Dienstag, 04.04.2023, 16:30 Uhr
Javier Llorente (Simon Fraser University, Canada)
Multijet production at the LHC: Event shapes, NNLO predictions and α_s
Abstrakt: Event shapes are a class of observables whose first non-trivial contributions in perturbative QCD arise from the radiation of a third jet. Measurements of such variables at hadron colliders can serve as a precision test of perturbative QCD. This talk will review the status of such measurements in the ATLAS experiment, as well as the comparison of these data to high-precision next-to-next-to-leading order predictions for three-jet production, which have become recently available. Fits of these theoretical predictions to measurements of Transverse Energy-Energy Correlations and their azimuthal asymmetry are performed to determine the value of the strong coupling constant αs at different energy scales, thus testing the running of the QCD coupling with unprecedented precision beyond the TeV scale.
Host: Michal Czakon