Theoretische Physik II

Seminar series @ TP2


It´s a pleasure to invite you to the first seminar series of our prospective Research Training Group. The third seminar will be on 18 July at 4:30 p.m. The talk will be by MSc. Christoph Haitz.

23. May 2023 - SE 31.00.017 - 4:30 p.m.

MSc. Manuel Kunkel
Title: Uncovering BSM scalars with neural networks

We study a simple extension of the Standard Model motivated by composite Higgs models, in which a doubly charged scalar decays to W+ t b, resulting in a 4t-like signature from pair production. We train neural networks to differentiate this BSM signal from the dominant SM backgrounds using jet images and kinematic data. We derive the discovery reach and expected exclusion limit at the LHC. In this context we highlight some key differences between standard image recognition and its application to particle physics.

MSc. Yanick Thurn
Title: Analytic continuation of lattice quantum Monte-Carlo (QMC) simulations unsing neural networks

In quantum many-body physics, the analytic continuation of Greens' functions is a well-known problem. The problem is ill-posed in the sense that the transformation kernel becomes chaotic for large energies and thus small noise creates huge differences in the resulting spectral density function. Some techniques in the field of machine learning, in particular neural networks, are known for handling this kind of problem. A network is trained to determine the spectral density from the imaginary part of the Greens function given by quantum Monte Carlo simulations. The network is able to recover the overall form of the spectral density function, even without adding constraints such as normalization and positive definiteness. There is no need to encode these constraints as regularizations since they are reflected automatically by the solution provided by the network. This indicates the correctness of the inversion kernel learned by the neural network.

20. June 2023 - SE 31.00.017 - 4:30 p.m.

MSc. Lucas Klein
Title: Cross-section measurement of top quark pair with additional b-jets at ATLAS

The top quark pairs with additional b-jets provide very interesting tests of QCD at higher orders. It also represents an important background to the SM processes directly probing the coupling of the Higgs boson with the top quark. I will highlight the cross-section measurements of this process in the dilepton final state using the data collected with the ATLAS detector. The dilepton final state provides very clean signature with some ambiguity of jets produced from the decay of the top quark and from the extra QCD radiation. My talk will also highlight the estimation of top-quark pair background in the signal events where either an additional c-jet or a light-flavour jet is mistagged.  

18. July 2023 - SE 31.00.017 - 4:30 p.m.

MSc. Christoph Haitz
Title: NLO QCD predictions for polarised ZW$^+$ production with semileptonic decay

With the help of the pole approximation, observables with polarised intermediate resonances can be calculated. Gauge-boson-pair production represents a particularly interesting class of processes to study polarisation. The definition of polarised signals at amplitudue level has enabled successful phenomenological studies of leptonically decaying vector bosons. The natural step forward from this is the investigation of bosons decaying into hadrons. In this talk I discuss the NLO QCD predictions for the production of a polarised ZW$^+$ pair, where the W$^+$ boson decays hadronically and the Z boson leptonically. Of particular interest are observables that are well suited for the discrimination amongst different polarisation states of both weak bosons. In addition I analyse the significant impact of NLO QCD corrections on differential distributions. 


After the seminar a barbecue will take place on Campus Hubland Nord if weather permits it. In case of bad weather we will meet at the Greek restaurant.