Particle Physics - Measuring Charm Mixing Parameters in D-4h

The LHCb experiment has unsurpassed capabilities for studying the phenomena of mixing and CP violation in the charm system. Although mixing in charm decays was first observed around 15 years ago, it is highly desirable to improve the knowledge of the parameters that drive this process. CP violation in mixing-related phenomena has not been seen, and any observation at the current level of precision would be an indicator of New Physics.

The student will embark on a programme of charm mixing and CP-violation measurements using four-body D decays, in particular the singly Cabibbo suppressed processes D->pi+pi-pi+pi- and K+K-pi+pi-. These decays have not been previously harnessed for such measurement, and offer promising sensitivity that is complementary to that obtainable from the two and three-body decays that have so far been exploited. He will do this with a model-independent approach that uses external knowledge of strong-phase parameters that are measured at the BESIII experiment in Beijing. The analysis will be based on data collected in Runs 1 and 2 of the LHC. Depending on the speed with which the analysis is conducted, he may also make a pilot measurement with early data collected in Run 3 with the upgraded LHCb detector, but this does not currently form part of the baseline plan. Another possible extension of the thesis work would be to contribute to the analysis of the BESIII data from which the strong-phase parameters are determined. Oxford is one of only two UK groups that are members of BESIII, and thus have unique access to these data.

The TORCH is a novel time-of-flight Cherenkov detector that is proposed for installation in LHCb Upgrade II in a decade's time. A vigorous programme of R&D is required to arrive at a final design that will have the necessary performance. The student will play a central role in this development. Likely areas of involvement include the evaluation of front end electronics for prototypes and the final detector; participation in data taking and analysis in test beam campaigns; and the improvement of reconstruction code. He will also benchmark the impact that the TORCH detector will have on the physics reach of LHCb. Central to the success of TORCH is the performance of its photodetectors, and there will be close association with industry, in particular the UK firm Photek who have been heavily involved in the evolution of the TORCH project until now.