# Potentielle Themen (BSc / MSc / PhD)

All bachelor and master students will be integrated in our group and work close together with a senior PhD student or Post-Doc on one of our current research topics. Some example of potential topics are:
• ## Measurement of B lifetimes

The LHCb experiment has access to a high statistic sample of cleanly reconstructed $B \rightarrow J/\psi X$ decays, such as $B^+ \rightarrow J/\psi K^+$, $B_d \rightarrow J/\psi K^*$ and $B_s \rightarrow J/\psi \Phi$. Using these decay modes we have the potential to perform world best measurement of B lifetimes. The main challenge is to properly derive the decay time acceptance which is sculpted due to trigger and selection cuts.
• ## CP violation in $B^0 \rightarrow J/\psi K_s$

CP violation in the B system was first discovered in the $B^0 \rightarrow J/\psi K_s$ decays at the B factories Babar and Belle in 2001. To repeat this analysis at LHCb although not as precise as at the B factories, will help us to understand potential origins of asymmetries (such as production or reconstruction asymmetries) which will be crucial for any future CP measurement.
• ## Rekonstruction of $B^0 \rightarrow J/\psi K^0$ ($\rightarrow$ lepton neutrino $\pi$) decays

One of the interesting analysis to study for the LHCb upgrade is the search for CPT violation in so called "cascade" decays. These are decays wich involve $B^0$ and $K^0$ oscillation in the decay chain and thus give rise to CP (CPT) violation. The most favorite decay in this context is $B^0 \rightarrow J/\psi K^0$ ($\rightarrow$ lepton neutrino $\pi$). Due to the missing neutrino in the final state, the B mass construction is non trivial. Based on MC studies the reconstruction method should be developed and the according signal efficiency evaluated. On a toy MC the potential rate of decays inside the LHCb acceptances should be studied. If the study predicts a significant rate already on the current LHCb data sample, a search for this signal on data will be performed.
• ## Measurement of branching ratio for $B_s \rightarrow J/\psi K_s$ decays

$B_s \rightarrow J/\psi K_s$ is a very important channel to estimate physics background to $B^0 \rightarrow J/\psi K_s$ decays, which are used to measure CP violation in the $B^0$ system. The current yield of $B_s \rightarrow J/\psi K_s$ decays is rather low. Multivariante analysis techniques (neural nets, boosted decision trees) will be exploited to enrich the yield and a branching ratio measurement will be performed.
• ## Hardware Development and Research in the LHCb Fibre Tracker Upgrade

The LHCb group at the Physikalisches Institut Heidelberg is looking for students at the Bachelor (diploma), Master and Doctorate level interested in the development and study of novel position tracking detectors for high energy physics applications for their thesis work. The primary focus will be on the radiation hardness, performance and feasibility of a new detector design using solid-state silicon photo-multipliers and plastic scintillating fibres for a large-area tracking detector for the upgrade of the LHCb experiment. Projects will include hardware development, including assembling and testing prototypes, along with systematic studies of the radiation damage tolerance of the components through lab testing, accelerator test beam studies and Monte Carlo simulations (FLUKA and GEANT). The student will gain a valuable knowledge of detector development in a high rate, intense radiation environment and can have a large impact on the design and structure of this novel detector.
In the past, the Heidelberg LHCb group contributed significantly to the development and the construction of the existing LHCb tracking detector at CERN. Doctoral, masters and diploma students were heavily involved in all steps of the necessary research program and contributed to the success of the project. Building on existing experience, we hope to also play a major role in the new project.

Interested students can contact: Dr. Blake Leverington (leverington@physi.uni-heidelberg.de)