Seminars WS21/22

Tue, 26.10.2021, 16:30 (Online)

Tristan du Pree (Nikhef)

Search for the Higgs boson decay to charm quarks at the ATLAS experiment



Since the discovery of the Higgs boson by the ATLAS and CMS experiments, almost a decade ago, its couplings to massive vector bosons and third-generation fermions have been firmly established. Also, the first evidence of the Higgs boson coupling to muons now starts to appear at the LHC. However, the couplings to lighter quarks are still very much unconstrained.
In this seminar, I will present the most recent search for the Higgs boson decay to charm quarks by the ATLAS collaboration, using the full LHC Run-2 dataset. To study the coupling to quarks of the second generation, we use dedicated flavour tagging algorithms to identify jets originating from beauty, charm, and lighter quarks. We categorise the events according to the number of jets, charm quarks, and leptons, and perform a combined fit to all data in 44 signal and control regions. As a validation of our analysis method, we measure diboson production with heavy vector boson decays to one or two charm quarks and we observe significances for these processes of 3.8 and 2.6 standard deviations. We don't observe Higgs boson decays to charm quarks and exclude enhanced signal strengths greater than 26 times the predicted value. For the first time, we place a direct constraint on the Higgs-charm coupling, at most 8.5 times the interaction strength in the Standard Model.
I'll end the seminar with an overview of complementary methods to probe the Higgs-charm coupling, a comparison with other experiments, as well as the future prospects for the LHC and beyond.


Host: Alexander Schmidt



Tue 23.11.2021, 16:30 (Online)

Juan Rojo (Vrije Universiteit Amsterdam & Nikhef)

The Path to Proton Structure at One-Percent Accuracy



In this talk I will review recent progress in our understanding of proton structure, as quantified by the parton distribution functions (PDFs). This progress not only enables the precision phenomenology program of the (HL)-LHC, but also makes possible addressing key open questions in QCD from the origin of nucleon mass and spin to the antimatter and heavy quark content of the nucleon. In particular I will present the recent NNPDF4.0 determination, a state-of-the-art global QCD analysis based on machine learning techniques and combining the information provided by almost 100 independent datasets. I will also discuss how the software framework used to produce NNPDF4.0 is made available as an open-source package together with documentation and examples. I will review the implications of NNPDF4.0 for important LHC processes, as well as for key topics in nucleon structure from strangeness and the large-x gluon to intrinsic charm.


Host: Malgorzata Worek



Tue 07.12.2021, 16:30

Gordon Watts (University of Washington)

New Computing Paradigms for HEP Analysis


Abstract: tbd

Host: Dennis Noll



Tuesday, 21.12.2021, 16:30 (Online)

Sebastian Wuchterl (DESY)

Status of top mass measurements


Abstract: tbd

Host: Michal Czakon




Tue 18.01.2022, 16:30 (Online)

Xavier Coubez (Brown University and RWTH Aachen University)

Jet tagging techniques


Abstract: tbd

Host: Alexander Schmidt




Tue 01.02.2022, 16:30 (Online)

Urs Wiedemann (CERN)

Heavy Ion Collisions at the LHC


Abstract: tbd

Host: Robert Harlander