Seminars SS 18

Tue 08.05.2018, 16.30 h (28B110)

Walter Winter (DESY-Zeuthen)

Fundamental physics tests with neutrinos traveling over cosmological distances

Abstract:
I briefly review the recent results from the IceCube experiment and introduce the particle astrophysics of neutrino sources. Then I focus on two applications for fundamental physics tests: physics beyond the Standard Model changing the neutrino flavor composition at detection, and propagation effects over cosmological distances - at the example of neutrino lifetime.

 

Tue 15.05.2018, 16.30 h (28B110)

Alexander Schmidt (RWTH)

Search for dark matter Axions with the MADMAX experiment

Abstract:
Axions are hypothetical particles that are attractive dark matter candidates. They can also solve the strong CP problem. While the parameter space for WIMP dark matter is continuously being constrained by countless experiments, there are only few experiments on the direct search for dark matter Axions. The talk will explain the
motivation and fundamental basics of Axionic dark matter and will describe a new experiment (MADMAX) that may potentially reach a sufficient sensitivity to discover dark matter Axions if they exist.

 

Tue 29.05.2018, 16.30 h (28B110)

Daniel Litim (University of Sussex)

Asymptotic safety of gauge theories and quantum gravity

 

Tue 05.06.2018, 16.30 h (28B110)

Albert De Roeck (CERN/University of Antwerp)

Searches for Long Lived Particles at the Large Hadron Collider

Abstract:
The Large Hadron Collider (LHC) is the highest energy particle collider operational in the world. One of its main scientific goals is the quest for signals beyond the Standard Model of particle physics.

In this seminar, we will discuss a special kind of searches conducted recently at several of the LHC experiments: the search for long lived particles. Particles such as heavy neutral scalars, long-lived supersymmetric particles, monopoles etc., do not decay at the interaction vertex, but will traverse the detectors and can produce detectable signals in the detector volume.

We will review the recent results and what we can learn from these searches for physics beyond the Standard Model. We will also discuss emerging opportunties at the LHC for new "small-scale" experiments that can cover in the near future additional searches for such new exotic particles, in a complementary way to the capabilites of the present LHC detectors.

 

Tue 12.06.2018, 16.30 h (28B110)

Anders Kvellestad (Oslo)

Chasing SUSY through parameter space - global fits in the MSSM

Abstract:
The most powerful approach for assessing the status of a BSM theory is to perform a global fit - a comprehensive and statistically rigorous comparison of theory predictions against all the available experimental results. In this talk I will give an introduction to BSM global fits and the recently released software package GAMBIT, an open-source tool for performing large-scale global fits. I will further present the results from GAMBIT global fits of GUT-scale and weak-scale parameterizations of the MSSM.

 

Tue 26.06.2018, 16.30 h (28B110)

Gregor Kasieczka (Hamburg)

Deep Learning in Particle Physics

Abstract:
Deep neural networks have quickly proven themselves as a versatile tool for many problems outside of physics. Examples include image classification, speech recognition and solution strategies for games like "Go". Simultaenously, the use of complex algorithms and ever more poweful computers is indispensible for modern particle physics. In this seminar we will explore different deep learning approaches, and discuss how they can be used - and are used - to achieve progress in physics at the LHC. This includes the discrimination of different kinds of particle jets, handling correlations and systematic uncertainties, dealing with pile-up as well as simulation and triggering.

 

Tue 10.07.2018, 16.30 h (28B110)

Christoph Langenbruch (RWTH)

Flavour Anomalies at LHCb

Abstract:
Precision measurements of heavy flavour observables are powerful probes for phenomena beyond the Standard Model (SM). Of particular interest are rare B-meson decays that are strongly suppressed in the SM,  and where new heavy particles can have large effects on branching fractions and angular distributions. In this area, several intriguing tensions with SM predictions recently emerged that are commonly referred to as "flavour anomalies". This talk will give an overview over the flavour anomalies, focussing on results from the LHCb experiment. Particular emphasis will be placed on tensions in tests of lepton universality, where extremely clean SM predictions are available. Furthermore, possible theoretical interpretations of the anomalies will be discussed.

 

Tue 17.07.2018, 16.30 h (28B110)

Angela Papa (University of Pisa/PSI)

Charged lepton flavour violation search with the MEGII experiment at PSI and future prospects

Abstract:
Lepton flavor violation (LFV) research is currently one of the most exciting branches of particle physics due to its high sensitivity to new physics. The observation of neutrino oscillations has clearly demonstrated that neutral lepton flavor is not conserved. This implies that charged LFV (cLFV) processes, such as the μ+ → e+ γ decay, can also occur in simple extended Standard Model (SM) versions (i.e. including Dirac neutrinos) which takes into account for neutrino oscillations, although strongly suppressed. On the other hand, Beyond SM (BSM) extensions strongly enhance the predictions for cLFV branching ratios. Therefore such decays are ideal probes for new physics. The MEG experiment at the Paul Scherrer Institut searches for the μ+ → e+ γ decay and has completed the data collection at the end of the 2013. The analysis of the full data set acquired in the period 2009-2013 for a total amount of 7.5 × 1014 stopped muons on the target has been recently completed and it will be presented. Using the full data sample we set a new upper limit on the branching ratio of this decay of 4.2 × 10−13 (90% confidence level): It is a factor 30 improvement over the previous limit set by the MEGA experiment and also the strongest bound on any forbidden particle decay. The strong scientific motivation to search for the μ+ → e+ γ decay pushes the collaboration for an upgrade of the MEG experiment aiming at improving the single event sensitivity by one order of magnitude: MEGII. The MEGII experiment has successfully performed a pre-engineering run during the 2017 and currently the 2018 full engineering run is in preparation.
During this seminar the status of the MEGII experiment will be given in detail. It will be followed by a discussion about future μ+ → e+ γ decay search prospects.

 

Tue 24.07.2018, 16.30 h (28B110)

René Reimann (RWTH Aachen)

Compelling Evidence for Neutrino Emission from a Blazar

Abstract:
On September 22, 2017 the IceCube online system sent out an alert reporting on a high-energy neutrino event called IceCube-170922A. Soon it was noticed that its location is consistent with TXS 0506+056, a known GeV blazar. Multi-wavelength follow-up observation by 18 observatories revealed that this source was flaring in very-high-energy gamma-rays. The probability to find a flaring gamma-ray source by chance in coincidence with a neutrino alert has been calculated to be on the 3σ level. In addition, IceCube analyzed 9.5 years of data looking for neutrino emission prior to but in the direction of the reported event. Allowing for a time-variable flux of neutrinos, IceCube found an independent 3.5σ excess in the direction of TXS 0506+056. In this talk, the findings by IceCube and the multi-wavelength observation are explained. The implications for multimessenger astrophysics will be discussed.