Seminars SS20

Tuesday, June 23, 2020, 4:30pm (zoom)

Steffen Schumann (Universität Göttingen)

The art of combining matrix elements and QCD parton showers


I will discuss concepts and techniques used for the matching  and merging of next-to-leading order hard-scattering matrix  elements with QCD parton showers in modern Monte Carlo  event generators. Furthermore, recent developments to also  include next-to-leading order electroweak corrections will be  highlighted.


Host: Robert Harlander




Tuesday, June 09, 2020, 4:30pm (zoom)

Melissa van Beekveld (Nikhef / Radboud University Nijmegen)

Power up your logarithm: the large impact of 'subleading' terms



Cross-sections in perturbative QCD are plagued by large  corrections from soft and collinear radiation. The most singular  terms are known to be universal, which allows their resummation  to all orders in the coupling, hereby curing the cross-section of  the large uncertainties. In this talk, I will give a broad  introduction as to how these large corrections arise, how  resummation solves the issue, and whether we can expect the same  universal structure for a class of next-to-singular contributions. We also discuss their numerical impact.


Host: Michael Krämer




Tuesday, May 26, 2020, 4:30pm (zoom)

Andreas Hinzmann (Hamburg University)

From raw data to published experimental results at the LHC



The collider experiments at the LHC are among the most complex particle detectors ever built and operated. Likewise, the process of analysing the raw data collected by these experiments to publish results on fundamental interactions of elementary particles is as complex as the detectors themselves. It required algorithm development for more than a decade. This talk gives a basic overview of the most important aspects of data reconstruction, calibration and analysis necessary for the study of fundamental interactions, taking as example the process of analysing raw data collected by the CMS experiment and covering state of the art techniques.


Host: Alexander Schmidt




Tuesday, May 12, 2020, 4:30pm (zoom)

Alexander Grohsjean (DESY)

Top quark spin: A window to new physics?


High precision measurements of the properties of elementary particles are essential to understand the Universe at smallest scales. However, they also might give us exciting insights to the largest scales of the Universe, such as the understanding of Dark Matter, and may provide an avenue to physics beyond the Standard Model (BSM). The analysis of observables with small systematic uncertainties in the phase space region of new physics are of particular interest.

In this talk, the first measurement of the full ttbar spin density matrix at the CMS experiment in proton-proton scattering at the Large Hadron Collider is presented. The general analysis concept and its application in the quest for BSM physics are highlighted. The measurement provides an important answer to an anomaly observed at ATLAS in 2018 and is used to constrain anomalous couplings in an Effective Field Theory framework with greatest sensitivity. It will also be shown how the tt spin density matrix can be utilized to enhance the sensitivity in searches for new scalar particles and how this could shed light on the nature of Dark Matter.


Host: Danilo Meuser