Seminare SS 19

Di. 02.04.2019 16:30 (28B110)

Stefano Gariazzo (IFIC Valencia)

Relic neutrinos and the PTOLEMY project

The Cosmic Neutrino Background (CNB) is a prediction of the standard cosmological model, but it has been never observed directly. Several methods of direct detection for the CNB have been proposed in the past and the most promising one is currently adopted to develop the PTOLEMY proposal. I will review some theoretical aspects of the CNB, including the calculation of the local density of relic neutrinos in the Milky Way, some proposed detection techniques and finally discuss the specific case of PTOLEMY, mostly from the point of view of perspectives in neutrino physics.


Di. 21.05.2019 16:30 (28B110)

Yoann Genolini (ULB, Brussels)

DM and compact objects

Due to their extreme density and low temperature, neutron stars (NS) are efficient probes to unveil interactions between standard model and dark matter (DM) particles. From elastic scatterings on NS material, DM can get gravitationally trapped by the star. The cooling of DM through further collisions may lead to the formation of a dense core which could collapse into a black hole, thus destroying the whole NS. I will show that from the observation of old NS, such a scenario leads to very stringent constraints on the parameter space of asymmetric DM, and I will detail the novelties we have introduced.


Di 01.12.2020 16:30 (Zoom)

Christoph Weniger (University of Amsterdam) 

Turbocharging dark matter research with simulator-based inference and differentiable programming



Dark matter constitutes the majority of mass in the Universe, but still its nature remains unknown. One way to study the mass of dark matter particles is to analyse the distribution and clumping of dark matter at small (sub-galactic) scales. Information about this small scale structure can be obtained from the analyses of gravitationally strongly lensed images of distant galaxies. However, due to the complexity of galaxy images and degeneracies between lens and source variations, such images are notoriously difficult to analyse. I will present a new fast, flexible and powerful analysis pipeline of strong lensing images that brings together a wide range of modern machine learning and differentiable programming methodologies, and that makes strong lensing image analysis fit for upcoming observations.

Host: Felix Kahlhoefer


Di. 28.05.2019 16:30 (28B110)

Andreas Meyer (DESY)

Physics at the HL-LHC

The High-Luminosity LHC (HL-LHC) is going to start operation in 2026. Upgrades of the experiments comprise substantially improved detectors with larger acceptance, better triggers, and enhanced background suppression. Until the end of the 2030s, an integrated luminosity of 3000 fb-1 of pp data will be recorded. Based on the recent new and precise results of LHC Run-2, the expectations for the physics yield at the HL-LHC have been updated. The report of the "Workshop on the Physics at the HL-LHC and Perspectives for the HE-LHC”,  input to the European Particle Physics Strategy Update 2018-2020, covers all aspects of HL-LHC physics. In my talk, I am presenting a selection of highlights.


Di. 15.12.2020 16.30 (Zoom)

Thorben Quast (CERN)

CMS HGCAL Overview



The CMS collaboration is preparing to build replacement endcap
calorimeters for the HL-LHC era. The new calorimeter endcap will be a
highly-granular sampling calorimeter (HGCAL) featuring unprecedented
transverse and longitudinal readout segmentation for both its
electromagnetic and hadronic compartments. The granularity together with
a foreseen timing precision on the order of a few tens of picoseconds
will allow for measuring the fine structure of showers, will enhance
pileup rejection and particle identification, whilst still achieving
good energy resolution. The regions exposed to higher-radiation levels
will use silicon as active detector material. The lower-radiation
environment will be instrumented with scintillator tiles with on-tile
SiPM readout. In addition to the hardware aspects, the reconstruction of
signals, both online for triggering and offline, represents a
challenging task - one where modern machine learning approaches are well
In this talk, the reasoning and ideas behind the HGCAL, the
proof-of-concept of its design in test beam experiments, and the
challenges ahead will be presented.

Host: Martin Erdmann 


Di. 10.11.2020 16:30 (Zoom)

Joachim Kopp (University of Mainz & CERN)

Neutrino Physics: Status and Prospects 



With the planned DUNE, Hyper-Kamiokande, and JUNO detectors, as well as
numerous smaller experiments, neutrino physics has become one of the
flagship disciplines of particles physics. In this colloquium, we review
some of the most exciting current and future developments in neutrino
physics. We begin by outlining the physics program of current and future
long-baseline neutrino oscillation experiments. We then discuss the
potential implication of various anomalies observed in neutrino
oscillation searches on particle physics and cosmology. Finally, we
highlight some of the interconnections between neutrinos and dark matter.

Host: Dr. Malgorzata Worek


Di. 18.06.2019 16:30 (28B110)

Belina von Krosigk (TRIUMF, Vancouver)

Searches for Dark Sector Particles with SuperCDMS SNOLAB

The Super Cryogenic Dark Matter Search (SuperCDMS) is a direct Dark Matter search experiment designed to observe nuclear recoils induced by WIMPs. However, it is also sensitive to Dark Matter particle candidates beyond the standard WIMP paradigm, which could create electron recoil signals in the cryogenic silicon and germanium detectors. The pool of candidates is rich and includes Dark Photons, ALPs (axion-like particles) and LDM (light Dark Matter) particles. Lacking knowledge of the particles that constitute the dark sector of the Universe it is essential to make the search for them as broad as possible. This talk will give an overview of the versatile dark sector particle search strategies at the upcoming SuperCDMS SNOLAB experiment and will highlight first results with R&D devices as well as the expected science reach of selected searches.


Di. 19.01.2021 16:30 (Zoom)

Merijn van de Klundert (DESY)

Analysis of the CP structure of the Yukawa coupling between the Higgs boson and τ leptons in proton-proton collisions at 13 TeV



The Higgs boson constitutes a pivotal particle in the Standard Model of
particle physics. It was discovered in 2012 by the ATLAS and CMS
experiments, and since then its characteristics have been reviewed by
both experiments.
This presentation focuses on the CP-structure of the couplings of the
Higgs boson to fermions and gauge bosons. After introducing the topic,
an overview is provided on the state-of-the-art results on Higgs-CP
measurements at the LHC from both the ATLAS and CMS experiment. The
recent CMS result on the CP-structure of the Higgs-tau Yukawa coupling.


Host: Werner Bernreuther


Di. 08.12.2020 16:30 (Zoom)

Giulio Settanta (Forschungzentrum Jülich)

First detection of solar neutrinos from the CNO cycle with the Borexino detector



Neutrinos are elementary particles which are known since many years as fundamental messengers from the interior of the Sun. The Standard Solar Model, which gives a theoretical description of all nuclear processes which happen in our star, predicts that roughly 99% of the energy produced is coming from a series of processes known as the “pp-chain”. Such processes have been studied in detail over the last years by means of neutrinos, thanks also to the important measurements provided by the Borexino experiment. The remaining 1% is instead predicted to come from a separate loop-process, known as the “CNO cycle”. This sub-dominant process is theoretically well understood, but has so far escaped any direct observation. Another fundamental aspect is that the CNO cycle is indeed the main nuclear engine in stars more massive than the Sun.

In 2020, thanks to the unprecedented radio-purity and temperature control achieved by the Borexino detector over recent years, the first ever detection of neutrinos from the CNO cycle has been finally announced. The milestone result confirms the existence of this nuclear fusion process in our Universe.  Here, the details of the detector stabilization and the analysis techniques adopted are reported. Final results are discussed, together with the implications for solar physics and astrophysics.

Host: Livia Ludhova



Di. 25.06.2019 16:30 (28B110)

Dietrich Bödeker (Uni Bielefeld)


I present a brief introduction to finite temperature quantum field theory, in particular for Quantum Chromodynamics (QCD). Applications in cosmology, like the effect on gravitational waves, the production of dark matter and of the matter-antimatter asymmetry are discussed.


Di. 26.01.2021 16:30 (Zoom)

Maria Ubiali (University of Cambridge)

New frontiers in the determination of the proton structure



The parametrization of the proton's structure via the determination of Parton Distribution Functions (PDFs) is a crucial theoretical input at the LHC. The PDF uncertainty is often a limiting factor in the accuracy of theoretical predictions. At the same time the LHC is delivering a number of precise measurements that provide precious information on the proton's structure.  In this seminar, I will give a broad overview on the theory behind and on the state-of-the-art of PDF determinations. I will then mention the new challenges that modern fits of PDFs face, due to the unprecedented precision of the LHC data.


Host: Malgorzata Worek


Di. 09.07.2019 16:30 (28B110)

Felice Pantaleo (CERN)

Towards a heterogenous computing farm for the CMS High Level Trigger

To fully exploit the physics reach of the High-Luminosity Large Hadron Collider, the LHC experiments are planning substantial upgrades of their detector technologies and increases of their data acquisition rates. Studies are ongoing to develop the Future Circular Collider (FCC) trigger and data acquisition infrastructure, which will have even higher requirements. The higher proton-proton interaction rate, pileup and event processing rate present an unprecedented challenge to the real-time and offline event reconstruction, requiring a processing power which is orders of magnitude larger than today. This exceeds by far the expected increase in processing power for conventional CPUs (at a fixed cost), demanding an alternative approach.
In recent years, Industry and High-Performance Computing centres have been successfully using heterogeneous computing platforms to achieve higher throughput and better energy efficiency, combining traditional processors with dedicated accelerators and matching each task to the most appropriate architecture.
The speaker will present the implications of the higher luminosity, pileup and event complexity for the trigger and data acquisition system of the Compact Muon Solenoid (CMS) experiment, and discuss the possibility of addressing them by employing a heterogeneous computing architecture. The speaker will also describe the main differences in the hardware and programming models between traditional CPUs and a widespread type of accelerator, general purpose GPUs, and discuss how they can be used together to explot their potential.
Finally, the speaker will present the Patatrack project, an incubator for R&D activities within the CMS collaboration aiming to use a heterogenous computing farm during the upcoming Run 3 (2021-2023), with the goal to improve the physics reach of the experiment and gain the necessary expertise in view of a wider deployment during the High-Luminosity runs at the LHC.


Di. 02.02.2021 16:30 (Zoom)

Thomas Becher (University of Bern)

Effective Theory for Jet Processes



Since its early days Soft-Collinear Effective Theory (SCET) has been advertised as an effective theory for jet processes, but the observables that have been resummed using this framework are so far mostly hadronically inclusive cross sections. As an example, I’ll discuss transverse momentum resummation and present precise results for the spectra of both single and multiple electroweak bosons. I’ll then turn to jet cross sections and explain why their resummation is much more involved. As an example of a resummed jet observable, I’ll present results for top production with a central jet veto.

Host: Michal Czakon



Di. 19.11.2019 16:30 (28B110)

Michal Bluj (Warsaw)

Testing CP structure of Higgs couplings at LHC

Violation of the CP symmetry is one of the Sakharov conditions required to explain the baryon asymmetry observed in Universe. Although the CP violation is already built in the Standard Model via quark mixing, its strength is not sufficient to explain the magnitude of the observed baryon asymmetry. This motivates searches for new sources of CP violation in the Higgs sector.


Di. 15.10.2019 16:30 (28B110)

Kumiko Kotera (Paris)

The Giant Radio Array for Neutrino Detection

The Giant Radio Array for Neutrino DetectionAbstract: The Giant Radio Array for Neutrino Detection (GRAND) project aims to detect ultra-high-energy cosmic neutrinos, cosmic rays, and gamma rays with a radio antenna array deployed over a total area of 200000 km2 in mountainous regions, in several favorable locations around the world. The strategy of GRAND is to detect air showers above 10^17 eV that are induced by the interaction of high-energy particles in the atmosphere or in the Earth crust, through its associated coherent radio-emission in the 50-200 MHz range. In its final configuration, GRAND plans to reach a sensitivity of ~10-10 GeV cm-2 s-1 sr-1 above 5*1017 eV and a sub-degree angular resolution. The 300-antenna pathfinder array, GRANDProto300 is planned to be deployed in 2021. It aims at demonstrating autonomous radio detection of inclined air-showers, and make measurements of the composition and the muon content of cosmic rays around the ankle energy. In this talk, we will show preliminary designs and simulation results, plans for the ongoing, staged approach to construction, and the rich research program made possible by the proposed sensitivity and angular resolution.


Di. 09.02.2021 16:30 (Zoom)

Mikael Kuusela (Department of Statistics and Data Science, Carnegie Mellon University)
Unfolding in High Energy Physics: A Statistician's Perspective



Differential cross section measurements in particle physics experiments are smeared by the finite resolution of the particle detectors. Using the smeared observations to infer the true particle-level spectrum is an ill-posed inverse problem, typically referred to as unfolding or unsmearing. The defining feature of this problem is that it is easy to go from the particle-level spectrum to the smeared observations but the inverse direction of inferring the quantity of interest based on the smeared data tends to produce highly unstable solutions. It is customary to address this using regularization which reduces the variance of the estimates at the expense of increased bias. While this can lead to well-behaved point estimates, it is extremely challenging to provide rigorous frequentist uncertainties for the regularized estimates. In this talk, I will first give an overview of the statistical techniques that are commonly used for regularized unfolding at the LHC. I will then demonstrate that some of these methods may seriously underestimate the statistical uncertainty and will explain why that is the case. I will then describe approaches that can be used to obtain improved frequentist uncertainty quantification in unfolding. I will argue that the key is to avoid explicit regularization and instead infer functionals of the unknown spectrum, such as integrals over wide histogram bins, that implicitly regularize the problem.

Host: Lutz Feld


Di. 23.06.2020 16:30 (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


Di. 26.05.2020 16:30 (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



Di. 12.05.2020 16:30 (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


Di. 03.12.2019 16:30 (28B110)

Sascha Caron (Radboud University, Nikhef)

Expanding the search for new physics via data-derived signal regions, automatisation and machine learning


Di. 21.01.2020 16:30 (28B110)


Peter Fackeldey (RWTH)

Higgs pair production status at LHC (Run II)

The measurement of the di-Higgs boson production is a direct test of the electroweak symmetry breaking in the standard model of particle physics (SM). The coupling strength between three Higgs bosons (self-coupling) determines the shape of the Higgs potential and thus the vacuum stability of the universe. The current Run II status of ATLAS and CMS is presented with results interpreted in non-resonant (SM) and resonant (BSM) Higgs pair production.


Di. 14.01.2020 16:30 (28B110)


Dirk Krücker (DESY Hamburg)

The modern Times of HEP Analysis

Deep Learning and the common data science tools have fundamentally changed the style of data analysis in High Energy Physics. The latest b-quark taggers used by the CMS experiment at the LHC are large Neural Networks and many of the legacy Run II publication on searches for New Physics will use Machine Learning. The talks introduces the use of Neural Nets in CMS with examples from b-jet tagging and searches for Supersymmetry.


Di. 17.12.2019 16:30 (28B110)

Matthias Schröder (KIT)

The Higgs Boson at the Top: ttH Status and Future

In the Standard Model (SM) of particle physics, the Higgs boson is deeply related to the mechanism that creates the masses of the elementary particles. A precise measurement of the Higgs boson properties and couplings offers a unique probe of this mechanism, and thus, plays a crucial role in testing the predictions of the SM and discovering potential new physics.
The coupling of the Higgs boson to the heaviest known quark, the top quark, is particularly exciting, as it is large, and therefore, has a strong impact on the consistency of the SM as well as on many new physics models. The best direct measurement of the top-Higgs coupling is achieved at the LHC in proton-proton collision events where a top quark-antiquark pair is produced in association with a Higgs boson (ttH production).
In the presentation, the first observation of the ttH production by the CMS experiment in 2018, which was achieved by combining analyses in several decay channels of the Higgs boson, will be reviewed, and an overview of the current status will be presented. As an example, a recent result in the bb decay channel of the Higgs boson will be highlighted, which establishes evidence for ttH production in this channel alone. The analysis benefits from a larger dataset, improvements of the CMS detector, as well as refined analysis methods exploiting advanced machine-learning techniques. Finally, prospects for future ttH measurements at the LHC and beyond will be discussed.