Semileptonic B Decay Anomaly

Master Thesis at LMU Munich, TU Munich
Since Mai 2017

The semileptonic decay \( B \longrightarrow D^{(*)} \ell \bar\nu_\ell \) has been extensively studied by the experiments Belle, BaBar and LHCb. All of these experiments have independently reported an excess of tauonic endstates \( \ell=\tau \) over the endstates with light leptons \( \ell=\mu, e \). The combined observations of all three experiments challenge lepton universality and thus the Standard Model at a four sigma level (see plot below). This is especially intriguing, as the anomaly occurs in a tree-level SM process. My Master's thesis considers the \( B \longrightarrow D^{(*)} \ell \bar\nu_\ell \) decay channel and is intended to be a mix of theoretical, phenomenological and experimental work. It is roughly split up in three parts:

  1. Getting an overview over new physics models that could accommodate the observed excess.
  2. Looking into the phenomenology of these models and considering (new) observables that are sensitive on (some of) these models.
  3. Using data from Belle I to check the sensitivity that can be obtained using these observables.
World averages for the measurements of R(D), R(Dstar)
The world average for the measurements of the observables \( R(D^{(*)}) \) currently shows a \( 4\sigma \) deviation from the Standard Model. Result of the Heavy Flavor Averaging Group from 2017.

Complex Organic Molecules in Protoplanetary Disks

Summer Program Project at TITECH
July 2017 till September 2017
Complex Organic Molecules (COMs) in protoplanetary disks have been the subject of extensive studies using chemical reaction networks (CRNs) (e.g. Walsh et al., 2014). The accuracy of these models depends on our knowledge of the relevant chemical processes. Some classes of reactions have been comprehensively studied, resulting in large databases like the UMIST database of astrochemistry, which lists more than 6000 gas-phase reactions. However, other classes of reactions, such as grain-surface reactions, still pose challenges.
By expanding the previously studied CRNs with additional grain-surface reactions that are currently studied in new laboratory experiments (and have so far mostly been considered in the context of meteorites), we tried to improve the description of COM formation in protoplanetary disks. More specifically, I have been using the existing simulation code to investigate the influence of physical and chemical parameters, such as temperature, density and activation energies, on the time evolution of the chemistry found on grains. Trying to automize some time-consuming manual tasks necessary for such studies, I wrote a framework of about 4000 lines of code to repeatedly run the simulation with different settings and to visualize the resulting datasets. I hope that this framework will enable future students to conduct similar studies much more efficiently, thereby opening new research possibilities.
More information: Experience Report Prof. Nomura; Final presentation (aimed at a general audience) [PowerPoint pptx, 5MB]
Flowchart of the analysis framework I wrote
Analysis framework, repeatedly calling the chemical reaction network (CRN), storing output and log files, parsing them and finally bringing them together for plotting/analysis.

Performance monitoring for LHCb DAQ

Summer Student Project at CERN/LHCb
July 2015 till September 2015
In 2020 the Data Acquisition (DAQ) of the LHCb experiment will be updated to feature a trigger-free readout. This requires an event builder network consisting of about 500 nodes with a total network capacity of 4 TBytes/s. DAQPIPE (Data Acquisition Protocol Independent Performance Evaluator) is a tool to simulate and evaluate the performance of such a DAQ system. The current implementation of DAQPIPE only gives rough feedback about the event building rate. The aim of this 10-week summer student project was to implement network monitoring for a more detailed performance evaluation of different transport protocols and to spot potential bottlenecks. First, several existing performance monitors were tested. To that end DAQPIPE was run together with Tau and the obtained performance data was plotted with ParaProf, JumpShot and Vampir. In the second stage of the project, a light-weight performance analysis tool was written from scratch by wrapping around the C++ MPI communication library to collect data.
Monitoring data sent by two readout units
Monitoring the data sent by two readout units (RUs). RUs collect incoming data fragments from different subdetectors and send it to builder units (BUs), which process the information.

Truth-level based estimation of the sensitivity to pMSSM models in events with one hard lepton

Thesis (BA Sc. in Physics) at LMU Munich
Based on the search for supersymmetry in final states containing one isolated lepton, jets and missing transverse momentum with proton-proton collision data recorded with the ATLAS detector at a center-of-mass energy of \( \sqrt s \) = 8 TeV in 2012, I looked into the estimation of the sensitivity to phenomenological MSSM models using the signal shape of truth level signal samples. These were then compared to the sensitivity as calculated with MC samples on which a full detector simulation and reconstruction had been performed. The agreement was found to be generally low. Several sources of error were ruled out, showing the necessity of a more detailed study of the underlying truth- and reco-level signal samples.
More information: Fulltext [pdf, 8.4MB]
CLs values obtianed by reco/truth level analysis
Comparing the CLs values obtained by reco level analysis (y axis) and truth level analysis (x axis). Ideally both values should roughly agree (resulting in the red line with \( x=y \)), but this is obviously not the case here.

Elliptic Functions

Thesis (BA Sc. in Mathematics) at LMU Munich
Central subject of the this are so called elliptic functions, meromorphic functions that are periodic in two directions, i.e. invariant under a translation of their argument by two linearly independent complex numbers. Among others, elliptic functions are of great use in number theory, in particular there are interesting connections to sums of divisors of natural numbers. Furthermore they are used in the theory of elliptic curves and elliptic integrals.
Imaginary part of the Weierstrass p functin
Imaginary part of the Weierstrass p function \( \wp \), an example of an elliptic function. Clearly visible are the two periods \( \wp(x+2) = \wp(x) = \wp(x+2i) \) throughout the domain.